Masaaki Abe

This study reports an effective peripheral decoration of organic donor-acceptor diads with B(C6F5)3 for stabilizing electrogenerated radical ions. By employing a common p-type organic semiconductor benzothienobenzothiophene (BTBT) as the donor, tetracoordinate boron complexes showed improved solution electrochemiluminescence (ECL) intensity, reaching a 156-fold increase compared to that of the parent diad. The unprecedented Lewis-pairing-induced ECL enhancement is attributed to the multiple roles of B(C6F5)3: 1) redistributing frontier orbitals, 2) facilitating electrochemical excitation, and 3) restricting molecular motions. Furthermore, B(C6F5)3 converted the molecular arrangement of BTBT from conventional 2D herringbones into 1D π-stacks. This robust, highly ordered columnar nanostructure allowed red-shifting of the crystalline film ECL with electrochemical doping through the electronic coupling pathways of BTBT. Our approach will facilitate the development of elaborate metal-free ECL systems.

Mixed-valence ruthenium trinuclear clusters containing dichloroacetates were synthesized, and the self-assembly of a single molecular adlayer composed of these clusters on a graphite surface was investigated by atomic force microscopy (AFM). AFM clearly revealed the dynamics of two-dimensional (2D) structure formation as well as the molecular characteristics of the adlayers at different electrochemical interfaces. The results verified that the design of metal complexes is important not only for redox chemistry but also for molecular assembly and nanoarchitecture construction.

The use of earth-abundant and inexpensive Co catalysts for carbon-hydrogen (CH) bond activation has received increasing attention because of the advantages including air stability. Although directing groups have been effectively introduced in substrates to promote C(sp3)H activation through chelation assistance, there is a lack of basic information about the isolated alkyl-Co complexes containing directing groups as polydentate ligands. In this study, we report the synthesis and characterization of an alkyl-Co(III) complex 2Co, prepared from a N,N -bis(8-quinolyl)malonamide derivative, the malonyl fragment of which was disubstituted by two ethyl groups. 2Co was straightforwardly obtained from a Co(II) salt without any use of chemical oxidants but in the presence of air, through selective -C(sp3)H activation. The combined NMR spectroscopic and X-ray crystal structural analyses revealed that the malonamide substrate was converted into a pentadentate ligand with an N4C set, acquiring a helical configuration around the Co(III) center. The non-innocent ligand properties of 2Co were unambiguously confirmed by UVvis spectroscopic, electrochemical, and DFT studies. Thermolysis of 2Co enabled C(sp3)N reductive elimination in the absence of chemical oxidants. The present study provides important insights into the reactivity of alkyl- Co(III) complexes with a defined coordination geometry around the Co center toward designing elaborate C(sp3)H functionalization systems.

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu6(Hmna)6]·7DMF (1·7DMF) and [Ag6(Hmna)6]·8DMSO (2·8DMSO), where H2mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λPL = 545 nm, ΦPL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λPL = 765 nm, ΦPL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (ΦPL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.

A new tetracopper(I) complex containing a cuboidal Cu4S4 core, [Cu4(dap)4], where dap1 is dibenzodiazepinethiolate(1), has been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. The monoanionic iminothiolate ligand dap1 renders the cluster framework exceptionally stable to retain the tetranuclear structure in solution, which allows us to examine for the first time the solution properties of this class of clusters, including UV-vis and NMR spectroscopy and cyclic voltammetry.

The synthesis of helical complexes is attracting increased attention because their chiral properties lead to a variety of functional applications. In this work, a series of neutral, dinuclear M(III) (M = Al, Ga, or In) triple-stranded helicates were prepared using a tetradentate bisiminopyrrole ligand (H L). An X-ray crystallographic analysis revealed that both right- (P) and left-handed (M) helical structures exist in the solid state for Al L , Ga L , and In L . The enantiomers were successfully resolved by chiral column chromatography, and the chiroptical properties of the complexes were characterized by circular dichroism, circularly polarized emission spectroscopy, and time-dependent density functional theory calculations. 2 2 3 2 3 2 3

New chiroptical chromophores, dinuclear triple-stranded helicates, composed of tetradentate ligands with aluminum(III) ions, are described. These are synthesized in two steps using inexpensive pyrrole derivatives, hydrazine, and aluminum chloride. These molecular architectures (ALPHY) show multi-color (cyan, yellow, and orange) photoluminescence in solution and in the solid-state, which depends on the substituents of the ligands. The photoluminescence quantum yields of helicates were up to 54 %. The right-handed (P) and left-handed (M) helicates are so stable that they do not undergo racemization in some solvents and are mirror images according to circular dichroism and circularly polarized luminescence (CPL) with an absolute luminescence dissymmetry factor (g ) of up to the 10 order. Mixing the different helicates produces white-light emission with CPL characters. This study offers a glimpse into the potential applications of chromophores with diverse photophysical properties. lum −3

Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a pi-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO2 surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of 7c-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7- dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO2. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.

The crystal structure of a new pyrazine-bridged trimer of oxo-centered triruthenium-carbonyl clusters formulated as [Ru3O(EtCOO)(6)(CO)(pyrazine)](2)[Ru3O(EtCOO)(6)(CO)(mu-pyrazine)(2)] (1) has been unequivocally determined by single-crystal X-ray diffraction (SC-XRD) analysis at 100 K. A supramolecular cyclic assembly of two trimers was formed via intermolecular COMIDLINE HORIZONTAL ELLIPSISCO contacts, which is further assembled into a three-dimensional orthogonal layer-by-layer stack via hydrogen bonds.

Two new photoluminescent multinuclear Cu(I) cluster complexes supported by monoanionic bidentate ligandN-methylbenzimidazolethiolate (Me-bimt(-)), [Cu-n(Me-bimt)(n)] withn = 4 (1) and 6 (2), have been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. For1and2, the Cu(I) ions and the Me-bimt(-)ligands construct a cubane-type {Cu4S4} and a hexagonal-prism {Cu6S6} frameworks, respectively. In the crystalline state, complexes1and2exhibit green (lambda(em) = 500 nm) and near-infrared (lambda(em) = 876 nm) emission, respectively, under UV irradiation (lambda(ex) = 365 nm) at room temperature. Both crystals reveal temperature-dependent dual emission below 200 K: complex1emits in the visible wavelength region (lambda(em) = 493 and 542 nm) and complex2in the visible to near-infrared wavelength region (lambda(em) = 752 and 973 nm) which are attributed to multiple photoexcited states at the cluster frameworks with distinct metal nuclearity.

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Mixed valency is a well-known phenomenon in which charge distributions can change via intervalence charge transfer. In addition, there are many other ubiquitous phenomena for charges such as proton transfer, zwitterionization, charge separation, and some supramolecular interactions. However, a basic understanding of the interface between mixed valency and other charge-involved phenomena remains poor. Recent progress is described in creating mixed-valence subspecies by introducing stimuli-responsiveness to conventional mixed-valence frameworks and interplay between mobile charges and charges introduced via light and ions.

Crystalline-state photochromism of a rhodium dithionite complex with n-propyl moieties was studied directly by performing single crystal X-ray diffraction experiments; a non-linear relationship between the degree of the conformational change of the n-propyl moiety and the degree of the photochromic reaction of the dithionite group (mu-O2SSO2) was observed at -173 degrees C.

Realization of molecular quantum cellular automata (QCA), a promising architecture for molecular computing through current-free processes, requires improved understanding and application of mixed-valence (MV) molecules. In this report, we present an electrostatic approach to creating MV subspecies through internalizing opposite charges in close proximity to MV ionic moieties. This approach is demonstrated by unsymmetrically attaching a charge-responsive boron substituent to a well-known organometallic MV complex, biferrocenium. Guest anions (CN- and F-) bind to the Lewis acidic boron center, leading to unusual blue-shifts of the intervalence charge-transfer (IVCT) bands. To the best of our knowledge, this is the first reported example of a zwitterionic MV series in which the degree of positive charge delocalization can be varied by changing the bound anions, and serves to clarify the interplay between IVCT parameters. The key underlying factor is the variable zero-level energy difference in the MV states. This work provides new insight into imbuing MV molecules with external charge-responsiveness, a prerequisite of molecular QCA techniques.

We report the synthesis of a new bistriarylamine series having a urea bridge and investigate its mixed-valence (MV) states by electrochemical and spectroelectrochemical methods. We found that the supporting electrolytes had unusual effects on potential splitting during electrochemical behavior, in which a smaller counteranion thermodynamically stabilized a MV cation more substantially than did a bulky one. The effects contrary to those reported in conventional MV systems were explained by zwitterionization through hydrogen bonding between the urea bridge and the counteranions, increasing the electronic interactions between two tri-arylamino units. Furthermore, we clarified the intervalence charge transfer characteristics of the zwitterionic MV state.

In this study, we report the generation of new mixed-valence (MV) subspecies with charge-separated (CS) characters from an unsymmetrical acceptor-donor-donor (A D D) triad. The triad was synthesized by attaching a dimesitylboryl group (A) to a D D conjugate that consisted of triarylamine (NAr3) units. The MV radical cation, obtained by chemical oxidation of the triad, exhibited a strong intervalence charge transfer (IVCT) absorption derived from the bis(NAr3)(center dot+) moiety in the near-IR region. The charge-separated MV (CSMV) state, obtained by photoexcitation of the triad, caused a blue shift in IVCT energy in the femtosecond transient absorption spectra, reflecting a bias of positive charge distributions to the D end site. This resulted from increased electron density at the A site and restructuring of the central D site from NAr3 to NAr2 sites. Interestingly, any shift in the IVCT energy that was caused by the polarity of the solvent was minimal, reflecting the unique characteristics of the CSMV state. These findings represent the first detailed analysis of the CSMV state, including a comparison with conventional MV states. Therefore, this work provides new insights into counterion-free MV systems and their applications in molecular devices.

Benzothienobenzothiophene (BTBT) and derivatives have received increasing attention as organic field-effect transistor materials and molecular conductors. This report presents the first synthesis of metal complexes involving a BTBT moiety, which was achieved by complexation of 2,2-bipyridyl complexes of Pt(ii) and Pd(ii) with dihydroxy-substituted BTBT (1) as a new -extended catecholato ligand ((t)Bu(2)Bpy = 4,4-di-tert-butyl-2,2-dipyridyl). The resulting complexes M((t)Bu(2)Bpy)(O2BTBT) (M = Pt (3Pt) and Pd (3Pd)) were characterized by UV-vis spectroscopy, density functional theory (DFT) calculations, and cyclic voltammetry. The electron donating ability of BTBT was substantially enhanced upon including two oxygen substituents followed by metal coordination. This enabled chemical oxidation of 3Pt and 3Pd with a mild chemical oxidant (ferrocenium hexafluorophosphate) and formation of the one-electron-oxidized state. While 3Pt and 3Pd exhibited an absorption band originating from a catecholate Bpy ligand-to-ligand charge transfer transition typical of this class of catecholato complexes, the radical cations exhibited a unique -* intramolecular charge transfer (ICT) transition absorption in which the and * orbitals were the newly incorporated benzothienothiophene-based donor and semiquinonato-based acceptor, respectively. The BTBT+ skeleton was electronically divided into two sites by the present chemical modification. The ICT properties of the complexes were found to be modulated by varying the metal ions. These findings offer a new approach to molecular design for (semi)conducting materials using optical properties.

In this study, we report synthesis of a new series of mixed-valence (MV) complexes having intervalence charge transfer (IVCT) energies variable from the first to the third telecommunication window. This wide-range modulation was achieved by variation of covalently-dimerized catecholato ligands, in combination with Pd(II) ions, which lowered the oxidation potentials and enabled access to MV states. Importantly, we found that regulation of the conjugation lengths enabled energy gap control and annulation of an additional benzene ring switched the nature of the IVCT transitions. These changes were accompanied by a cross-over from moderately delocalized Class II to delocalized Class III character according to the Robin-Day classification. Through accurate comparisons with well-known ferrocene counterparts and their heteroconjugate, our non-innocent ligand-based approach is found to be effective for controlling IVCT parameters. These findings offer a new approach to materials design for electro-optic switching.

We demonstrate herein a novel molecular strategy for crystalline-state luminescence color tuning in the entire visible region by adopting thermochromic dual phosphorescence of coordination complexes. As crystals, a new cubane-type tetranuclear copper(I)-idodido complex with 2-benzylpyridine N-donor ligands 1 shows a sequential phosphorescence color change from yellow (298 K) to red and finally to blue (78 K) in the crystalline state across the color space area, in which relative intensity ratio of the triplet cluster-centered ((CC)-C-3) and triplet charge transfer ((CT)-C-3) bands in the dual-emission is reversibly controlled with temperature.

The distinct piezochromic luminescent responses of charge-transfer inclusion crystals, which consist of small aromatic guest molecules with naphthalenediimide derivatives, are reported. Reversible multichromism is observed over the entire visible region in response to high pressure, whereas a weak response to mechanical grinding is evident. High-pressure single-crystal X-ray diffraction analysis and TD-DFT calculations clearly suggest that high compression induces a closer arrangement with a short interfacial distance between small aromatic guest molecules and naphthalenediimide derivatives, which is proposed as the origin of the drastic luminescent color change.

A phosphorus(v) complex of porphycene [P(OEPc)(OMe)2]PF6 (OEPc = 2,3,6,7,12,13,16,17-octaethylporphycenato dianion) has been synthesized and structurally characterized as the first porphycene derivative incorporating nonmetal elements in the macrocyclic cavity. An extremely low energy level of the LUMO is observed, which is rationalized by the low-lying π* orbital of the porphycene ring coupled with the insertion of the highly-inductive pentavalent phosphorus centre. The compound is luminescent in bright red with a quantum yield of 22.7% in CH2Cl2 at 298 K.

Among the coenzyme B-12-dependent enzymes, methylmalonyl-CoA mutase (MMCM) catalyzes the carbon-skeleton rearrangement reaction between R-methylmalonyl-CoA and succinyl-CoA. Diethyl 2-bromomethyl-2-phenylmalonate, an alkyl bromide substrate having two different migrating groups (phenyl and carboxylic ester groups) on the beta-carbon, was applied to the electrolysis mediated by a hydrophobic vitamin B-12 model complex, heptamethyl cobyrinate perchlorate in this study. The electrolysis of the substrate at -1.0 V vs. Ag-AgCl by light irradiation afforded the simple reduced product (diethyl 2-methyl-2-phenylmalonate) and the phenyl migrated product (diethyl 2-benzyl-2-phenylmalonate), as well as the electrolysis of the substrate at -1.5 V vs. Ag-AgCl in the dark. The electrolysis of the substrate at -2.0 V vs. Ag-AgCl afforded the carboxylic ester migrated product (diethyl phenylsuccinate) as the major product. The selectivity for the migrating group was successfully tuned by controlling the electrolysis potential. We clarified that the cathodic chemistry of the Co(III) alkylated heptamethyl cobyrinate is critical for the selectivity of the migrating group through mechanistic investigations and comparisons to the simple vitamin B-12 model complex, an imine/oxime-type cobalt complex.

Metal-coordinated por-phyrin and related compounds are important for developing, molecular architectures that mimic enzymes. Porphycene, a structural isomer of porphyrin, has shown unique properties in semiartificial myoglobin. To explore its potential as a molecular building block, we studied the molecular assembly of nickel(II) tetra(n-propyl)porphycene (NiTPrPc), a metalloporphycene with introduced tetra n-propyl moieties, on the Au(111) electrode surface using in situ scanning tunneling microscopy. Because of the low molecular symmetry of NiTPrPc, the molecular assembly undergoes unique phase transitions due to conformational change of the n-propyl moieties. The phase transitions can be precisely controlled by the electrode potential, demonstrating that the latter can play an important role in the porphycene molecular assembly on Au surface. This new discovery indicates possible uses of this porphycene framework in molecular engineering.

Two new porphycenes functionalized with ferrocenyl pendants have been synthesized and characterized spectroscopically and structurally. The porphycene-based emission in porphycene-ferrocene dyads was switched on and off by the reversible control of the ferrocenyl pendant redox states. Transient absorption spectroscopy with a femtosecond laser-pulsed technique has successfully detected the picosecond charge-separated excited state of the dyad upon Q-band excitation of the porphycene ring.

Oxidative electropolymeization of an axially bound, bithiophene-pyridine complex of ruthenium(III)-porphycene [Ru(TPrPc) (btp)2]PF6 (1) gives a submicrometer-thick, polymeric film on an ITO electrode with a crystalline morphology. The polymeric film, the first example of axially linked multimetalloporphycene coordination arrays, exhibits highly stable and reproducible electrochromic response with high electrochromic efficiency upon electrochemical control over the metal-centered electron transfer process (Ru(II)/Ru(III)).

Preparation, characterization, and properties of a cyano bridged complex containing the Ru-3(mu(3)-O) cores, [{Ru-3(mu(3)-O) (mu-CH3COO)(6)(py)(2)}(2)(mu-CN)](PF6) ([1] PF6) (py = pyridine), are reported and compared with the properties of [{Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(2)}(mu-CN){Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(CO)}] (2). The cyclic voltammogram of [1](+) in 0.1 M (n-Bu)(4)NPF6-CH2Cl2 solution with an Ag/AgCl reference electrode showed a series of redox waves assigned to the processes Ru-3(II,II,III)/ Ru-3(II,III,III) (-1.70 V, -1.52 V), Ru-3(II,III,III)/Ru-3(III,III,III) (-0.37 V, -0.19 V), Ru-3(III,III,III)/Ru-3(III,III,IV) (+1.08 V), and Ru-3(III,III,IV)/Ru-3(III,IV,IV) (+2.03 V). Upon bridge formation the redox waves of the C-bonded Ru-3 moiety of [1](+) stay at the similar potential region to those of Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(2)(CN) (3) with a unidentate CN-, so that the enhancement of the pi-back donation does not operate, indicating that the Ru3O core is not a good p-donor. Complex 2 showed five redox waves for the processes Ru-3(II,II,III)/Ru-3(II,III,III) (-1.15 V), Ru-3(II,III,III)/Ru-3(III,III,III) (-0.21 V, +0.55 V), and Ru-3(III,III,III)/Ru-3(III,III,IV) (+1.05 V, +1.35 V). The redox potential (-1.15 V) of the Ru-3(II,II,III)/Ru-3(II,III,III) process of the Ru-3(py) (CO) unit in 2 showed a negative shift in comparison to that (-0.84 V) of [Ru-3(II,III,III)(mu(3)-O) (mu-CH3COO)(6)(py)(2)(CO)]. The infrared spectroelectrochemistry of [1](+) and 2 in 0.1 M n-Bu4NPF6-CH2Cl2 solutions revealed that the frequencies of the stretching vibration n(CN) of the cyanide increased with the increase in the isovalent oxidation states of [1](+) but those in the Ru3O-based mixed-valence states, Ru-3(II,III,III) - Ru-3(III,III,III), and Ru-3(III,III,III) - Ru-3(III,III,IV), were significantly smaller, which was possibly due to the effective electronic coupling through the CN bridge between the two Ru-3 units with different oxidation states. In contrast, such coupling was not observed for 2 that has two Ru-3 units with significantly different ligand environment. (C) 2015 Elsevier B.V. All rights reserved.

Crystal structures and solid-state emission properties of tetraalkyl 4,4'-dimethyl-2,2'-bipyrrole-3,3',5, 5'-tetracarboxylates (alkyl = methyl, ethyl, and isopropyl) have been investigated. Single crystal X-ray diffraction studies revealed that all bipyrroles are co-planar due to an intramolecular hydrogen bonding. The isopropyl derivative exhibited a C=O center dot center dot center dot pi interaction in the solid-state and showed the longest emission wavelength because of increase in structural flexibility. (C) 2015 Elsevier Ltd. All rights reserved.

Two ruthenium(II) carbonyl complexes of porphycene, (carbonyl)(pyridine)(2,7,12,17-tetra-n-propylporphycenato) ruthenium(II) (1) and (carbonyl)(pyridine)(2,3,6,7,12,13,16,17-octaethylpor-phycenato) ruthenium(II) (2), have been structurally characterized by single-crystal X-ray diffraction analysis. Cyclic voltammetry has revealed that the porphycene complexes undergo multiple oxidations and reductions in dichloromethane and the reduction potentials are highly positive compared to porphyrin analogs. UV-light irradiation (400 nm or shorter wavelength region) of a benzene solution of 1 and 2 containing external pyridine leads to dissociation of the carbonyl ligand from the ruthenium(II) centers to give the corresponding bis-pyridine complexes. The identical reaction has been also studied for a porphyrin derivative (carbonyl)(pyridine)(2,3,7,8,12,13,17,18-octaethylporphyriato) ruthenum(II) (3). The first-order kinetic analysis has revealed that the photosubstitution of all of the compounds occurs in the order of 10(-3) s(-1) at 298 K but proceeds faster for complexes of porphycene (1 and 2) than that of porphyrin (3).

A series of multiply meso-substituted porphycenes has been prepared by acetoxylation of 2,7,12,17-tetra-n-propylporphycene (H2TPrPc), and the molecular structure of 9,10-diacetoxy-2,7,12,17-tetra-n-propylporphycene (2a) determined by single-crystal X-ray diffraction analysis. The H-1 NMR and optical properties have also been investigated. (C) 2014 Elsevier Ltd. All rights reserved.

A new heterometallic diruthenium(III) magnesium(II) complex functionalized with four pyrenecarboxylate fluorophores 1 has been synthesized and structurally characterized. Fluorescence from the pyrene moieties in 1 was nearly completely quenched in CH2Cl2 (>98%), but turn-on fluorescence was successfully observed after regioselective substitution of the carboxylates bridging the heterometallic Ru(III)center dot center dot center dot Mg(II) sites.

A new cyano-bridged dimeric oxo-centered triruthenium complex [{Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(2)}(mu-CN){Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(Lpy-ss)}](+) (py = pyridine, Lpy-ss = (C5H4N-CH2NHC(O)(CH2)(4)CH(CH2)(2)SS) ([1](+)) has been prepared, characterized, and confined on an Au(111) surface to form self-assembled monolayers (SAMs) (1/Au). The redox and IR spectroscopic properties observed for the discrete ions are essentially preserved in its SAMs. The molecules of SAMs 1/Au stand up with the cyano groups tilted to the gold surface. The electronic structures of 1/Au in different oxidation states have been studied by in situ infrared spectroscopy monitoring the stretching modes of the cyano group. The extent of cyano-mediated electronic communications between two triruthenium units in the SAMs has been successfully tuned by simply changing the electrolyte solutions from 0.1 M n-Bu4NPF6-CH2Cl2 to aqueous 0.1 M HClO4. (C) 2013 Elsevier B.V. All rights reserved.

The preparation and properties of a new cyano complex containing the Ru-3(mu(3)-O) core, [Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(2)(CN)] (1; py = pyridine), are reported. Complex 1 in CH2Cl2 showed intense absorption bands at 244, 334, and 662 nm, corresponding to a pi-pi* transition of the ligand, cluster-to-ligand charge transfer, and intracluster transitions, respectively. The cyclic voltammogram of 1 in 0.1 M (n-Bu)(4)NPF6-CH2Cl2 showed redox waves for the processes Ru-3(II,II,III)/Ru-3(II,III,III), Ru-3(II,II,III)/Ru-3(III,III,III), and Ru-3(III,III,III)/Ru-3(III,III,IV) at E-1/2 = -1.49, -0.26, and +1.03 V vs Ag/AgCl, respectively. The first two redox potentials are more negative by ca. 0.2 V in comparison with the corresponding potentials of [Ru-3(mu(3)-O)(mu-CH3COO)(6)(py)(3)](+). This is in sharp contrast to the positive shifts of the corresponding waves of [Ru-3(II,III,III)(mu-CH3COO)(6)(py)(2)(CO)]. Density,/ functional theory (DFT) calculations of [Ru-3(II,III,III)(mu(3)-O)(mu-CH3COO)(6)(py)(3)], [Ru-3(II,III,III) (mu(3)-O)(mu-CH3COO)(6)(py)(2)(CN)](-), and [Ru-3(II,III,III),(mu(3)-O)(mu-CH3COO)(6)(py)(2)(CO)] showed that the positive charge of the ruthenium is delocalized over the triruthenium cores of the first two and is localized as Ru-II(CO){Ru-III(py)}(2) in the CO the difference in the it interactions of the two ligands with the triruthenium cores. complex. The calculations explain

A post-synthetic method has been developed to synthesize novel asymmetric porphycenes bearing two different substituents on the meso-positions. Nitration of 9-acetoxy-2,7,12,17-tetra-n-propylporphycene with AgNO3 in CH3COOH/CH2Cl2 occurs regioselectively at the 19-position of the macrocycle to give 9-acetoxy-19-nitro-2,7,12,17-tetra-n-propylporphycene (3a) which was readily converted to 9-acetoxy-19-amino-2,7,12,17-tetra-n-propylporphycene (4a) by the reduction with SnCl2 in pyridine. (C) 2013 Elsevier Ltd. All rights reserved.

A new mu-oxo-bis(mu-acetato)diruthenium(III) complex bearing two pyridyl disulfide ligands {[Ru-2(mu-O)(mu-OAc)(2)(bpy)(2)(L-py center dot SS)(2)](PF6)(2) (OAc = CH3CO2-, bpy = 2,2'-bipyridine, L-py center dot SS = (C5H4N)CH2NHC(O)(CH2)(4)CH(CH2)(2)SS) (1)} has been synthesized to prepare self-assembled monolayers (SAMs) on the Au(111) electrode surface. The SAMs have been characterized by contact-angle measurements, reflection absorption surface infrared spectroscopy, cyclic voltammetry, and reductive desorption experiments. The SAMs exhibited proton-coupled electron transfer (PCET) reactions when the electrochemistry was studied in aqueous electrolyte solution (0.1 M NaClO4 with Britton Robinson buffer to adjust the solution pH). The potential-pH plot (Pourbaix diagram) in the pH range from 1 to 12 has established that the dinuc.lear ruthenium moiety was involved in the interfacial PCET processes with four distinct redox states: (RuRuIII)-Ru-III(mu-O), (RuRuIII)-Ru-II(mu-OH), (RuRuII)-Ru-II(mu-OH), and (RuRuII)-Ru-II(mu-OH2). We also demonstrated that the interfacial redox processes were modulated by the addition of Lewis acids such as BF3 or Al3+ to the electrolyte media, in which the externally added Lewis acids interacted with mu-O of the dinuclear moiety within the SAMs.

Novel oxo-centered, acetate-bridged trinuclear ruthenium clusters functionalized with two pyridine ligands with thienyl substituents, [Ru3O(CH3COO)(6)(CO)(L1)(2)] (1) and [Ru3O(CH3COO)(6)(CO)(L2)(2)] (2), where L1 = 4-(2-thienyl)pyridine and L2 = 4-(2,2'-bithienyl)pyridine, have been synthesized and characterized. The molecular structure of 2 has been determined by single-crystal X-ray diffraction. One-electron oxidation of 2 with silver(I) cation has led to the isolation of a CO-dissociated product, [Ru3O(CH3COO)(6)(H2O)(L2)(2)]PF6 (3 center dot PF (6) ), and subsequent reaction with 4-dimethylaminopyridine (dmap) gave [Ru3O(CH3COO)(6)(dmap)(L2)(2)]PF6 (4 center dot PF (6) ). Linear metallopolymers containing the {Ru3O(CH3COO)(6)} groups have been deposited onto indium-tin oxide surface via oxidative electropolymerization of 2, 3 center dot PF (6) , and 4 center dot PF (6) . These metallopolymer thin films exhibit three-color electrochromism in the UV/Vis and near-IR region associated with the Ru-3 (II,III,III), Ru-3 (III,III,III), and Ru-3 (III,III,IV) oxidation states.

A Pd(II) complex, Pd(TPrPc-OH) (1, TPrPc-OH = 9-hydroxy-2,7,12,17-tetrapropylporphycenato dianion), has been synthesized and characterized. H-1 NMR spectroscopy revealed that compound 1 exists as its enol form in solution. The H atom of the hydroxy group in 1 was exchanged with deuterium on addition of ethanol-d (6). UV-visible spectra showed a red shift of the Q band of 1 in THF compared with that of the acetoxy derivative Pd(TPrPc-OAc) (2, TPrPc-OAc = 9-acetoxy-2,7,12,17-tetrapropylporphycenato dianion). The pK (a) value of the hydroxy group in 1 was determined, by means of a UV-visible titration experiment, to be 10.56. A cyclic voltammogram of 1 in a mixture of THF and Britton-Robinson buffered aqueous solution revealed one-electron and one-proton coupled transfer in the oxidation process in the pH range from 2.7 to 10.5, which was identified by pH-varying experiments and the Pourbaix diagram. Transient absorption spectroscopy revealed that an electron-transfer reaction occurred from the triplet excited-state of 1 to 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) upon pulse laser irradiation at 532 nm. Such an intermolecular photoinduced electron-transfer reaction was not observed between the Ni analog, Ni(TPrPc-OH), and DQ. The reaction rate constant, k (q), was indicative of a kinetic isotope effect with k (q(H))/k (q(D)) = 1.7, supporting the belief that the exited-state electron transfer from 1 to DQ is accompanied by proton transfer.

Hydrogenated tetrapropylporphycenes, 2,3-dihydro-2,7,12,17-tetrapropylporphycene 1 and its Ni-II complex 2, have been prepared and the hydrogenation effects on their electronic structure characterized. A one-electron reduction of 2 promotes dehalogenation of organic halides whose observation is unprecedented for the porphycene compounds.

Two new oxo-centred trinuclear ruthenium clusters supported by six dichloroacetate ligands, [Ru3(μ3-O)(μ-CHCl 2COO)6(CH3OH)3]CHCl2COO (1) and [Ru3(μ3-O)(μ-CHCl2COO)6(pyridine) 3] (2), have been synthesised and characterised by spectroscopic methods, electrospray ionisation mass spectrometry, single-crystal X-ray diffraction, and cyclic voltammetry. Due to the strong inductive effect of the dichloroacetate ligands, the redox potential of 2 was shifted to the positive side (∼1.0V or more) relative to the acetate analogue [Ru3(μ3-O) (μ-CH3COO)6(pyridine)3], and also the rate of pyridine/pyridine-d5 exchange reaction of 2 in CD3CN was retarded with the rate constant of kex298K=1. 9×10-8s-1 which is 105-fold smaller than the value for [Ru3(μ3-O)(μ-CH3COO) 6(pyridine)3]. Highly positive activation parameters obtained for 2, ΔH‡=138±7kJmol-1 and ΔS‡=71±20JK-1mol-1, illustrate a dissociative activation pathway in which rupture of the Ru-N(pyridine) bond is involved in the rate-determining step. © 2012 CSIRO.

The title compound, [Yb(C5HF6O2)(2)(C20H14N4)(H2O)]Cl center dot CH3OH center dot H2O, adopts an eight-coordinated geometry around the Yb-III atom consisting of a 4'-(4-pyridyl)-2,2': 6',2 ''-terpyridine (pytpy) ligand, two 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac) anions and an aqua ligand. In the solid state, the compound forms supramolecular chains running along the b-axis via intermolecular hydrogen bonds between the Yb-OH2 unit and the N-atom donor of the 4-pyridyl pendant of pytpy, with an O center dot center dot center dot N distance of 2.686 (4) angstrom. A chloride counter-anion and lattice methanol and water solvent molecules occupy a hydrophilic columnar space along the coordination chains. O-H center dot center dot center dot Cl hydrogen bonds occur. The two water molecules and the four trifluoromethyl groups are disordered over two sets of sites, each with different occupancy ratios.

Three new mu-oxo-bis(mu-acetato)diruthenium(III) complexes,trans(mu-O,OH2)-[Ru2(mu-O)(mu-CH3COO)2(bpy)2(H2O)2][PF6]2.3H2O ([1][PF6]2.3H2O; bpy = 2,2'-bipyridine), trans(mu-O,CN)-[{Ru2(mu-O)(mu-CH3COO)2(bpy)2}2{mu Ag(CN)2}{mu Ag2(CN)3}][Ag(CN)2][Ag2(CN)3](CH3CN)4(CH2Cl2) (2), and cis(mu-O,CN)-[Ru2(mu-O)(mu-CH3COO)2(bpy)2(CN)2]center dot CH3OH center dot H2O([3]center dot CH3OH center dot H2O), have been prepared and their X-ray crystal structures determined. Whereas [1]2+ and 3 are discrete species, 2 is a polymer in which the AgCN groups act as bridges through RuCN(or NC)Ag linkages. The discrete complexes dissolve in common solvents, but 2 is only slightly soluble in acetonitrile and dimethyl formamide (DMF) to give fragmented species (denoted as 2') in solution. Redox waves of 3 were observed at 0.83 (Epc) and +0.76 V (E1/2) versus Ag/AgCl in a solution of 0.1 M nBu4NPF6 in CH2Cl2, which correspond to the Ru2II,III/Ru2III,III and Ru2III,III/Ru2III,IV processes, respectively. The corresponding redox couples (E1/2) of [1]2+ were observed at 0.31 and +0.76 V in 0.1 M NaClO4 aqueous solution. Significantly more negative potentials of the Ru2II,III/Ru2III,III couple for the two cyano complexes (E1/2 = 0.77 V for 2') are noted. Complexes [1]2+, 2', and 3 exhibit strong visible absorption bands at max = 566 nm (= 12600 M1cm1; in H2O), 636 nm (21000 M1cm1; in acetonitrile), and 558 nm (18000 M1cm-1; in H2O), respectively. Density functional theory (DFT) molecular orbital calculations have been carried out for [1]2+, trans(mu-O,CN)-[Ru2(mu-O)(mu-CH3COO)2(bpy)2(CN)2] (2a, a model compound for 2'), 3, [Ru2(mu-O)(mu-CH3COO)2(py)6]2+ ([4]2+), and trans(mu-O,py)-[Ru2(mu-O)(mu-CH3COO)2(bpy)2(py)2]2+ ([5]2+; py = pyridine). It was revealed that the frontier orbitals of these complexes are dominated by the Ru(dp)mu-O(pp) type p systems. For the cyano complexes, energies of these p-type MOs are lifted up by the interaction with CN, so that the energy difference with the upper bpy p(*) orbitals becomes smaller. Thus, whereas the visible absorption bands of [1]2+, [4]2+, and [5]2+ are ascribed to the transitions within the p system metal-to-metal charge transfer (MMCT), those of 2' and 3 are ascribed to the HOMO-to-ligand p(*) (bpy) transition metal-to-ligand charge transfer (MLCT) and to the mixture of MMCT and MLCT (HOMO1 to p(star)), respectively.

A series of porphycenes bearing acetoxy and hydroxy groups at the meso-positions have been prepared and fully characterized: H2TPrPc-OH, [Ni(TPrPc-OH)], H2TPrPc-OAc, and [Ni(TPrPc-OAc)], where TPrPc-OH: 9-hydroxy-2,7,12,17-tetrapropylporphycenato dianion and TPrPc-OAc: 9-acetoxy-2,7,12,17-tetrapropylporphycenato dianion. H2TPrPc-OH is structurally determined by single-crystal X-ray diffraction, showing the enol-form in the solid state. The introduction of the electron-donating hydroxy group to the meso-position decreases the HOMO-LUMO gap by ca. 0.2 eV relative to the unsubstituted parent porphycene due to the remarkable destabilization of the HOMO level. This is experimentally confirmed by red shift of the Q band in the UV-vis spectra (in CH2Cl2), negative shift of the E-1/2 (in 0.1 M n-Bu4NPF6-THF), and also supported by DFT calculations. In aqueous THF, an irreversible oxidation of H2TPrPc-OH and [Ni(TPrPc-OH)] appears to be pH-dependent, with a negative E-pa shift upon increasing the solution pH (in the region from 3.0 to 10.5) with slopes of -62 and -63 mV per pH unit for H2TPrPc-OH and [Ni(TPrPc-OH)], respectively, indicating the occurrence of {1H(+)/le} proton-coupled electron transfer.

This paper reports the synthesis and characterization of a novel series of chain-like compounds where oxo-centered triruthenium cluster moieties are bridged by 4,4'-bipyridine (4,4'-bpy) spacers. A reaction of solvent-coordinated triruthenium "monomer" precursor [Ru(3)O(CH(3)CO(2))(6)(CO)(CH(3)OH)(2)] with a 0.1 equimolar amount of 4,4'-bpy in CH(3)OH gave mixture of chain-like compounds containing "dimers" to "tetramers" which were cleanly separated by column chromatography and characterized by spectroscopic and electrochemical methods. Cyclic voltammetry revealed that all chain-like compounds exhibit reversible and stepwise redox processes in solution with very weak intramolecular coupling between the triruthenium components across the 4,4'-bpy bridge. Photo-induced dissociation of CO from the compounds and electrode surface binding were also investigated.

Recent progress in the redox chemistry of multimetallic transition-metal complexes and clusters is reviewed. Special attention is paid to high-nuclearity complexes wherein redox-active sites (e.g., ferrocenyl pendants or Ru centers) are assembled in a close proximity with a well-defined geometry via the covalent or coordination bonds. A special emphasis is placed on literature survey for paddlewheel diruthenium(II,III) complexes coordinated by axial or equatorial ferrocenyl ligands, polyferrocenyl compounds in the form of wire, star, and ring, ferrocenyl-based dendrimers, and ligand-mediated molecular triangles and squares. Finally, future prospects of these mixed-valent systems are briefly discussed.

2,7,12,17-Tetra-n-propylporphycenatodihalotin(IV) complexes ([Sn(TPrPc)X-2], X = F, Cl, and Br) were synthesized and their photophysical properties were investigated. These complexes exhibit strong absorptions in the red region (600-630 nm). Strong quenching was observed during the fluorescence emission of the dibromotin(IV) complex, which is caused by an intramolecular heavy-atom effect. The complexes emit NIR phosphorescence in 1-iodopropane at room temperature and the intensity of the emission of the dibromotin(IV) complex is found to be smaller than that of the dichlorotin(IV) complex. The quantum efficiency (Phi(Delta)) of generation of singlet oxygen using the dibromotin(IV) complex IS the highest among the porphycenatotin(IV) complexes (Phi(Delta) = 0.79). Photooxidation of 1,3-diphenylisobenzofuran catalyzed by the complexes upon irradiation with red light (over 600 nut) was studied and a rapid oxidation of the substrate was observed when using the dibromotin(IV) complex.

At the right places: Owing to substitution-lability difference in disparate metal centers, an oxo-centered heterometallic trinuclear acetato complex [Ru2MgO(CH3COO)6(py)3] (py = pyridine; see picture) undergoes site-selective substitution of propionates and ferrocenycarboxylates in a stepwise manner. The new substituted families have been successfully separated by chromatography and fully characterized.

We present here an in situ scanning tunneling microscopy (STM) study of potential-induced reactions of oxo-centered acetato-bridged triruthenium clusters on Au(111) under electrochemical conditions, in which (i) reversible interconversion between two different redox states of the cluster and (ii) spontaneous dissociation of CO from the cluster were probed and visualized. It is known that the triruthenium complex [Ru-3(mu O3-)(mu-CH3COO)(6)(CO)(4-methylpyridine){(NC5H4)-CH2NHC(O)(CH2)(10)S}] (1), which is in the mixed-valent {(Ru-II-CO)(RuRuIII)-Ru-III} state, on Au(111) is one-electron oxidized to cationic complex 1(+) which corresponds to a {(Ru-III-CO)(RuRuIII)-Ru-III} oxidation state. The redox reaction is reversible on a cyclic voltammetry timescale. Complex 1(+) undergoes irreversible dissociation of CO in an aqueous phase on a longer timescale (ca. minutes) to fonn an aqua ligand-coordinated complex, 2(+), which is expressed as ((Ru-III-OH2)(RuRuIII)-Ru-III). The reversible redox reaction (1 reversible arrow 1(+)) and the irreversible ligand substitution reaction (1(+) -> 2(+)) were independently examined with in situ STM in a monolayer level by visualizing molecular-sized spots showing a different extent of brightness in STM images. We show here that the molecular-sized spots corresponding to 1, 1(+), and 2(+) are resolved by their brightness, which strongly depends on both the oxidation states and the ligand nature of the clusters. By employing multiple fast scans at an applied potential of +0.80 V vs. Ag/AgCl, we obtained STM images that follow the irreversible 1(+) -> 2(+) reaction on the surface, from which a rate constant of the CO release was calculated to be 1.9 (+/- 0.2) x 10(-2)s(-1) (25 degrees C; in contact with 0.1 mol dm(-3) aqueous HClO4 solution). The difference in brightness of the molecular spots is rationalized in terms of orbital-mediated tunneling by considering the difference in electronic states of the d pi-p pi system in the mu 3-O trirutheniurn cluster.

We report here an unprecedented utility of redox-active transition-metal complexes as heat-shielding materials. A poly(vinyl alcohol) film containing mixed-valent cluster [Ru3-(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(3)](PF6)(3) (1) (mbpy(+) = 1-methyl-4,4'-bipyridinium cation), which strongly absorbs light in the near-infrared region, shows heat-shielding characteristics whose efficiency is found to highly depend on the redox state of the cluster dye.

New synthetic precursors for CO-coordinated, oxo-centred triruthenium(II,III,III) complexes with varied, carboxylato groups [Ru 3O(RCO2)6(CO)(solvent)2] where R = C2H5, CH3 and C6H5 have been prepared and characterised. Among the series, the propionato-bridged complex [Ru3O(C2H5CO2) 6(CO)(THF)2] (1) was structurally determined by single-crystal X-ray crystallography. Cyclic voltammetry revealed that the benzoato-bridged complex [Ru3O(C6H5CO 2)6(CO)(C2H5OH)2] in 0.1 mol dm-3 nBu4NPF6/DMF undergoes two consecutive one-electron processes assignable to the redox of the Ru3(μ 3-O) core, the redox potentials of which are highly dependent on the electron-donating/accepting nature of the carboxylato groups. UV-light excitation of the compounds in CH3CN resulted in the dissociation of CO to form the tris(CH3CN) compounds [Ru3O(RCO 2)6(CH3CN)3] (R = C 2H5, CH3 and C6H5). These compounds are highly useful as synthetic precursors to a wide range of μ3-oxo-trirutherium derivatives with well-defined redox responses. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

A new strategy is proposed for the fabrication of photochemical pattern of a self-assembled monolayer (SAM) of an oxo-centered tri-ruthenium (Ru-3) cluster on a gold electrode surface. The fabrication was achieved under combined photochemical and electrochemical controls. By this strategy, the patterned SAM surfaces terminated with different kinds of moiety groups such as carbon monoxide (CO), nitric oxide (NO) and a successive layer of Ru-3 cluster by ligand-exchange reaction are obtained with high yields.

This paper reports synthesis and electrochemistry of six-coordinate ruthenium porphyrin isomers including six novel porphycene complexes with substituted pyridines in the axial positions, in which redox potential control of reversible Ru-II/R-III processes is successfully achieved over a 0.7-V potential region by varying the axial ligands and tetrapyrrole ligand structure and substituents.

Coordination of nitric oxide (NO) to a self-assembled monolayer (SAM) of a triruthenium (Ru-3) cluster, [Ru-3(mu(3)-O)(mu-CH3COO)(6)(CO)(L-1)(L-2)](0)(L-1 =[(NC5H4)CH2NHC(O)(CH2)(10)S-](2),L-2=4-methylpyridine), on a gold electrode surface has been studied by electrochemical and in situ infrared (IR) spectroscopic measurements. Ligand substitution reaction of NO for carbon monoxide (CO) ligands in the SAM strongly depends on the oxidation state of the terminal Ru-3 cluster. NO can be introduced into the Ru-3 Cluster in the SAM with a high yield after one-electron oxidation of the Ru-3 core to a oxidation state, while no coordination reaction occurs at the initial oxidation state of the Ru-3 cluster. The kinetics of the NO coordination and desorption processes is also evaluated by time-resolved in situ IR spectroscopy. Finally, we demonstrate that the SAM with NO/CO randomly mixed ligands at a desired ratio can be constructed on the gold surface by tuning a suitable oxidation state of the Ru-3 cluster under electrochemical control.

Interfacial ligand substitution of triruthenium(III) complexes confined on gold as a monolayer has proven to be useful to construct molecular heterostructures by quantitatively incorporating 4,4'-bipyridine-anchored diruthenium(III) complexes, whose multi-step redox sequence is reversibly tuned by proton-coupled electron-transfer reactions.

An in situ approach for rapid growth of multilayers of redox-active triruthenium cluster complexes has been developed under electrochemical potential control of the gold electrode, the formation process being successfully probed by cyclic voltammetry and AFM images.

Densely packed redox-active self-assembled monolayers (SAMs) of monocarbonyl trimthenium complexes [Ru-3-(mu(3)-O)(mu-CH3COO)(6)(CO)(MPY)(C10PY)] (1) (mpy, 4-methylpyridine; C10PY, {(NC5H4)CH2NHC(O)(CH2)(10)S-}(2)), [Ru-3(mu(3)-O)(mu-CH3COO)(6)(CO)(mu-C10PY)] (2), and [{Ru-3(mu(3)-O)(mu-CH3COO)(6)(CO)(mpy)}(2)(eta-C10PY)] (3) have been constructed on an Au(111) electrode surface. They were characterized by infrared reflection absorption spectroscopy (IRRAS), spectroscopic ellipsometry, and contact angle measurement as well as cyclic voltammetry. Redox potential of the SAMs of 1 at the interface of aqueous electrolyte solutions shifted negatively as the concentration of HClO4 increased from 0.01 to 1.0 mol dm(-3) with the slope of 0.059 V/decade and as the electrolyte was changed from H2SO4 (0.79 V vs. Ag vertical bar AgCl) to HNO3 (0.69 V) and HClO4 (0.59 V) at a fixed concentration of 0.1 mol dm(-3). No significant difference in the redox potential was observed between the acid and its sodium salt. The effect is explained, as previously reported for the ferrocenylalkanethiol and non-carbonyl triruthenium SAMs, in terms of the effective ion pair formation in the order ClO4- > NO3- > SO42-. The rate of the CO dissociation reaction of the complex in the SAMs (complete within a few minutes at room temperature) that occurs in the oxidation state of Ru-3(III,III,III) was not very sensitive to the applied electrode potential (0.6-4.8 V), but increased by ca. 2.5 times as the concentration of HClO4 (0-01-1.0 mol dm(-3)) was lowered, and by ca. one-order of magnitude as the electrolyte anions was changed from ClO4- to SO42- and NO3-.

Two consecutive one-electron reductions of the mixed-metal trinuclear complexes [RuIII2MII(μ3-O)(μ- CH3COO)6-(S)(bzpy)2] {(M = Co, S = H 2O) and (M = Ni, S = N,N′-dimethylformamide); bzpy = 4-benzoylpyridine} in acetonitrile give stable "double" mixed-valence states where both Ru2II,III and (bzpy-)(bzpy) states coexist. Splitting of the ligand-based redox waves, (bzpy) 2/(bzpy-)(bzpy)/(bzpy-)2, is 0.35 and 0.34 V for the Co and Ni complexes, respectively. © 2007 The Chemical Society of Japan.

An oxo-bridged diruthenium(III) complex was immobilized on a Au(111) electrode through the coordination by terminal pyridyl groups of self-assembled monolayer of alkyl chains, and the immobilized complex underwent proton-coupled electron-transfer reactions in a very wide pH range (2-12) with remarkable monolayer durability for multiple potential cycles.

Reactions of a Re-VII complex [Re-VII(O)(3)(tpenH-kappa(3) N,N',N"')ClO4)(2) ([1](ClO4)(2]) (tpen = N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine) that has a free bis(2-pyridylmethyl)amino group with Fe-III and Cu-II (or Cu-I) complexes in solution afforded three new mixed-metal complexes. From X-ray structural analyses, the counter anions (EO4-) of the isolated complexes are a mixture of ReO4- and the original ClO4-. The former was most likely produced by the decomposition of [1](2+) during reaction. The tetranuclear Re-VII-Fe-III complex [{Re-VII(O)(3)(mu-tpen-kappa(3) N,N'',N'": kappa(3) N',N"'',N'''')}(2)Fe-2(III)(mu-O)(mu-CH3COO)(2)](4+) ([2](4+)) has an oxodi(acetato)-bridged diiron(III) unit with two [Re-VII (O)(3)(tpen-kappa(3) N,N'',N'")](+) groups coordinated to each iron(III) ion. Structures of the dinuclear Re-VII-Cu-II complexes depend on the reactants. The reactions with Cu-II(ClO4)(2) in CH3OH/CH3CN and Cu-I(PPh3)(2)CH3CN in CH2Cl2/CH3CN afforded [Re-VII(O)(3)(mu-tpen-kappa(3) N,N'',N'":kappa(3),N',N'''',N'''')Cu-II(CH3CN)](3+) ([3](3+)) and [Re-VIII(O)(3)(mu-tpen-kappa(3) N,N",N''':kappa N-3',N'''',N'''')(CuCl)-Cl-II](2+) ([4](2+)), respectively. The Cu centers have an axially elongated octahedral structure with a bis(2-pyridylmethyl)amino moiety and CH3CN for [3](3+) or Cl- of solvent origin for [4](2+) coordinated in the tetragonal plane. The axial sites are occupied by two weakly coordinated EO4- ligands in [3](3+) or EO4- and bridging Cl- from a neighboring complex cation in [4](2+).

UV-vis and H-1 NMR spectra provide unambiguous evidences for the disproportionation reactions of ((ReO)-O-V(tpen)](3+) to give [(ReO)-O-IV(tpen)](2+) and [Re-VII(O)(3)(tpenH-kappa(3) N,N",N''')](2+) (tpen = N,N,N',N'-tetrakis(2-pyridyimethyl)ethylenediamine) in 2:1 ratio with the important participation of water molecules.

Oxidation states and CO ligand exchange kinetics in a self-as-sembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru3(μ 3-O)(μ-CH3COO)6(CO)(L1)(L 2)] (L1 = [(NC5H4)CH 2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coor dination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.

Photoresponsive self-assembled monolayers (SAMs): Photoexcitation of a CO-bearing trinuclear ruthenium cluster assembled on an Au(111) electrode results in dissociation of CO to form a H2O-terminated SAM (see picture). This is the first well-defined example of clean conversion of a redox-active molecular film by using light stimulus. (Figure Presented).

Photodissociation of CO from oxo-centered trinuclear ruthenium clusters [Ru3(μ3-O)(μ-OOCCH3) 6(CO)L2] (L = pyridine (py): 1; 4-cyanopyridine (cpy): 2; methanol: 3) dissolved in organic solvents has been examined. Upon photolysis (≥290 nm, a 450-W Xe lamp), an absorption peak at 585 nm observed for 1 in CH3CN decreases its intensity and a new absorption band appears and grows at 896 nm. This spectral change, presenting isosbestic points, corresponds to photosubstitution of CO in 1 to form [Ru3(μ 3-O)(μ-OOCCH3)6(CH3CN)(py) 2] 4. Photoexcitation of carbonyl complexes 2 and 3 in CH 3CN also affords the corresponding CH3CN-coordinated complexes [Ru3(μ3-O)(μ-OOCCH3(CH 3CN)(cpy)2] 6 and [Ru3(μ 3-O)(μ-OOCCH3)6(CH3CN) 3] 7, respectively. The photosubstitution reactions (excitation wavelength, ≥290 nm) are well described by the first-order kinetics: k = 7.3 × 10-4 5-1 for 1, 4.9 × 10-4 s -1 for 2 and 5.1 × 10-4 s-1 for 3 (298 K). In the presence of a 100-fold excess of py, photolysis of 1 yields a tris(py) complex [Ru3(μ3-O)(μ-OOCCH 3)6(py)3] 5 via photochemical loss of CO followed by coordination of py. The overall reaction (photochemical and thermal) is also confirmed by 1H NMR spectroscopy. The dissociative character of the photosubstitution is supported by negligible effects of the concentration of the entering pyridine molecule, the nature of solvents and the type of terminal monodentate ligands (other than CO) attached to the cluster. Quantum yield measurements with varied excitation wavelengths have shown that absorption bands located in the UV region (<400 nm) play a principal role in photosubstitution, whereas an absorption band in the visible region (centered at ∼580 nm), ascribed to an "intracluster" charge transfer, is not at all responsible for photosubstitution.

A highly selective ligand exchange reaction is realized in the self-assembled monolayer (SAM) of a triruthenium cluster on a gold electrode surface under precise electrochemical potential control. CO as well as NO molecules, which are known to play key roles in many chemical, biological, and environmental systems, can be efficiently introduced into the SAM by electrochemically tuning the electronic state of the Ru site. These unique surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution and could be used for the elucidation of the electron-transfer mechanism in a biological system as well as in the development of molecular sensors and devices.

Reactions of oxo-centered triruthenium acetate complexes [Ru3O(OAc)6(py)2(CH3OH)](PF6) (py = pyridine, OAc = CH3COO-) (1) with nearly equimolar amounts of dppa [bis(diphenylphosphino)acetylene] or dppen [trans-1,2-bis(diphenylphosphino)ethylene] gave [Ru3O(OAc)6(py)2(L)](PF6) (L = dppa, 2; dppen, 3). With 2.4 equiv of 1, the reactions provided diphosphine-linked triruthenium dimers, [[Ru3O(OAc)6(py)2]2(L)](PF6)2 (L = dppa, 4; L = dppen, 5), respectively. Similarly, the reactions of [Ru3O(OAc)6(L')2(MeOH)]+ [L' = dmap (4-(dimethylamino)pyridine), 1a; L' = abco (1-azabicyclo[2.2.2]octane), 1b] with dppen gave dppen-linked dimers, [[Ru3O(OAc)6(dmap)2]2(dppen)](SbF6)2 (6) and [[Ru3O(OAc)6(abco)2]2(dppen)](BF4)2 (7), respectively. The chemical reduction of 2, 4, and 5 by hydrazine afforded one- or two-electron-reduced, neutral products, Ru3O(OAc)6(py)2(dppa) (2a), [Ru3O(OAc)6(py)2]2(dppa) (4a), and [Ru3O(OAc)6(py)2]2(dppen) (5a), respectively. The complexes were characterized by elemental analyses, ES-MS, UV-vis, IR, and 31P NMR spectroscopies, and cyclic and differential-pulse voltammetries. The molecular structures of compounds 2, 4, 5, 5a, 6, and 7 were determined by single-crystal X-ray diffraction. In 0.1 M (Bu4N)PF6-acetone, the monomers and dimers of triruthenium clusters show reversible and multistep redox responses. The two triruthenium cluster centers in dimers undergo stepwise reductions and oxidations due to the identical redox processes of the individual Ru3O cluster cores, suggesting the presence of electronic communications between them through the conjugated diphosphine spacer. The redox wave splitting mediated by dppa containing an ethynyl group (C triple bond C) is found to be more extensive than that by dppen containing an ethenyl (C=C) one. It appears that the redox wave splitting is enhanced by the introduction of electron-donating substituents on the auxiliary pyridine rings.

A pair of seven-coordinate oxorhenium complexes of N,N,N′,N′- tetrakis(2-pyridylmethyl)ethylenediamine (tpen), [ReIVO(tpen)] (ClO4)2 (1) and [ReVO(tpen)](ClO 4)3 (2), and its R-1,2-propylenediamine analogue (R-tppn), have been prepared. X-ray structural analyses indicate that the structure of complex cation in 1 is best described as a monocapped trigonal prism with the oxo ligand as a cap. The four pyridylmethyl nitrogen atoms are essentially planar. On the other hand, the structure of complex cation in 2 is approximated as a pentagonal bipyramid, in which the four pyridyl nitrogen atoms take a tetrahedrally distorted arrangement. The structural difference is discussed in terms of different d-electron numbers. The μeff value of 1 at 300 K is 1.99 B.M. which corresponds to S = 1/2, while 2 is diamagnetic. The complexes show a reversible redox wave (Re(IV/V)) at +0.31 V vs Ag/AgCl in 0.1 M (n-C4H9)4NPF6 acetonitrile solution. In acetonitrile-aqueous buffer solution (2 < pH < 12), in addition to a pH independent Re(IV/V) wave at +0.18 V vs Ag/AgCl, a pH-dependent quasi-reversible Re(III/IV) wave with a slope of -0.056 V/pH-unit was observed, indicating that the relevant Re(III) species is [Re(OH)(tpen)]2+. The weak absorption peaks of 1 (in acetonitrile) at 836 and 511 nm and those of 2 (in water) at 800, 633, and 408 nm may be assigned to d-d transitions, while the peaks at 428, 381, and 361 nm of 1 may be of charge transfer origin.

Interfacial electron-transfer properties and CO-dissociation reactions at redox-active multilayers which were prepared from trinuclear ruthenium cluster molecules have been examined by cyclic voltammetry. The series of multilayers (up to five layers) assembled on gold electrodes show a single-step, reversible, multi-electron redox processes whose redox potentials are finely tuned by the number of Ru 3 components involved in the layers and are also affected by the nature of electrolyte anions. Electrochemical oxidation of the surface-confined CO-terminated multilayers (0.1 M HClO 4 aq., 298 K) induces dissociation of CO from the top layer, resulting in the change of the cyclic voltammograms. The redox-induced CO-dissociation reaction for each of the multilayers obeys the first-order kinetics, in which the rate constants range in the order 10 -2 s -1 (298 K).

The ligand-ligand redox interaction separated by di-, tri-, and hexanuclear cluster units is discussed in terms of the splitting of the redox waves (ΔE (L)) and the comproportionation constants (K com(L)) of the ligand-based mixed valence state. Although two redox-active monodentate ligands in the mononuclear ruthenium(II) complexes (either cis or trans configurations) do not show appreciable splitting in their reduction waves, interestingly those separated by giant triruthenium and hexarhenium cluster units clearly show splitting. The molecular orbital considerations in the literature suggest that these units possess some π-type molecular orbitals composed of metal dπ and possibly ligand pπ orbitals. Absence of the redox interactions in oxo-bridged diruthenium(II) and oxo-centered trirhodium(III) complexes where such π molecular orbitals (including an antibonding one) are fully occupied, indicates the importance of empty π* orbitals for the ligand redox communication. © 2004 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Hexarhenium(III) complexes with terminal isothiocyanate ligands, [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)(NCS)(6)] (1) and (L)(4)[Re(6)(mu(3)-Se)(8)(NCS)(6)] (L(+) = PPN(+) (2a), (n-C(4)H(9))(4)N(+) (2b)), have been prepared by three different methods. Complex 1 was prepared by the reaction of [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] with molten KSCN at 200 degrees C, while 2b was obtained by refluxing the chlorobenzene-DMF (2:1 v/v) solution of [Re(6)(mu(3)-Se)(8)(CH(3)CN)(6)](SbF(6))(2) and [(n-C(4)H(9))(4)N]SCN. The [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-) anion was also obtained from a mixture of Cs(2)[Re(6)(mu(3)-Se)(8)Br(4)] and KSCN in C(2)H(5)OH by a mechanochemical activation at room temperature for 20 h and isolated as 2a. The X-ray structures of 1 and 2a.4DMF have been determined (1, C(70)H(144)N(10)S(14)Re(6), monoclinic, space group P2(1)/n (No. 14), a = 14.464(7) A, b = 22.059(6) A, c = 16.642(8) A, beta = 113.62(3) degrees, V = 4864(3) A(3), Z = 2; 2a.4DMF, C(162)H(144)N(14)O(4)P(8)S(6)Se(8)Re(6), triclinic, space group P1 (No. 2), a = 15.263(2) A, b = 16.429(2) A, c = 17.111(3) A, alpha = 84.07(1) degrees, beta = 84.95(1) degrees, gamma = 74.21(1) degrees, V = 4098.3(8) A(3), Z = 1). All the NCS(-) ligands in both complexes are coordinated to the metal center via nitrogen site with the Re-N distances in the range of 2.07-2.13 A. The redox potentials of the reversible Re(III)(6)/Re(III)(5)Re(IV) process in acetonitrile are +0.84 and +0.70 V vs. Ag/AgCl for [Re(6)(mu(3)-S)(8)(NCS)(6)](4)(-) and [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-), respectively, which are the most positive among the known hexarhenium complexes with six terminal anionic ligands. The complexes show strong red luminescence with the emission maxima (lambda(max)/nm), lifetimes (tau(em)/micros), and quantum yields (phi(em)) being 745 and 715, 10.4 and 11.8, and 0.091 and 0.15 for 1 and 2b, respectively, in acetonitrile. The data reasonably well fit in the energy-gap plots of other hexarhenium(III) complexes. The temperature dependence of the emission spectra and tau(em) of 1 and [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] are also reported.

Layer-by-layer metal-cluster molecular multilayers are fabricated onto preorganized self-assembled monolayers on Au electrode surfaces. The molecular building block, [Ru3(μ3-O)(μ-CH3COO)6 (bpy)2(CO)] (bpy=4,4′-bipyridine), is applied by displacing the water ligand on the cluster core (see picture), which is precisely controlled through the electrode potential. The series of multilayers transport electrons across the molecularly linked backbone.

Reaction of ReVOCl3(PPh3)2 with an equimolar amount of tpen affords fac-[ReVIIO3 (η3-tpenH)](ClO4)2 (1), in which the tpen ligand coordinates to the fac-ReVIIO3 center in a η3-mode, and the dangling bis(2-pyridylmethyl)amine arm in 1 is subsequently used to produce a heterobimetallic complex fac-,fac-[Re VIIO3 (μ-η3:η 3-tpen)Re1 (CO)3](ClO4)2.

A series of (μ-oxo)bis(μ-acetato)diruthenium(III) complexes containing two pyridine (py) ligands and varied N-heterocyclic ligands in the positions trans and cis to μ-O, respectively, have been prepared to study py/py-d5 exchange reactions using 1H NMR spectroscopy. The diruthenium(III) complexes under investigation are [Ru2(μ-O)(μ-CH3COO)2(py)6] (PF6)2 (1), [Ru2(μ-O)(μ-CH3COO)2(bpy)2 (py)2](PF6)2 (2), [Ru2(μ-O)(μ-CH3COO)2(acpy) 4(py)2](FF6)2 (3), and [Ru2(μ-O)(μ-CH3COO)2(dmbpy) 2(py)2](PF6)2 (4), where bpy=2,2′-bipyridine, acpy=4-acetylpyridine, and dmbpy=4,4′-dimethyl-2,2′-bipyridine. Pseudo-first order rate constants for the ligand-exchange reactions are 10-6-10-5 s-1 for 1-4 in CD3CN at 298 K. It is found that the rate of the py/py-d5 exchange reactions is controlled by the electronic nature of the cis-oriented ancillary ligands, while the exchange mechanisms are tuned principally by the ligand steric factors. The activation parameters (ΔH‡ and ΔS‡) indicate that exchange reactions proceed through the dissociative (D) or the interchange dissociative (Id) mechanism for 1 and 3. Negative ΔS‡ values observed for 2 and 4 suggest a significant contribution of incoming ligands to the exchange pathway. The kinetic and thermodynamic parameters for the diruthenium series and the corresponding data for Ru-based oxo bridged trinuclear complexes established previously are compared and discussed. © 2002 Elsevier Science B.V. All rights reserved.

A porphyrin ball: An octahedral arrangement of six porphyrins is achieved by the coordination of 5-(4-pyridyl)-10,15,20-tritolylporphyrins (H2PyT3P) to the octa(μ3-S/μ3-Se)hexarhenium(III) core. Six porphyrin ligands are arranged virtually in an S6 manner as the X-ray structural analysis of [Re6(μ3-S)8(H2PyT 3P)6](SbF6)2 shows (see picture).

A series of the octahedral hexarhenium(III) complexes containing a variable number of diphosphine (diphos) or diphosphine-monoxide (diphosO) ligands have been prepared by the substitution of the diphosphine Ph2P(CH2)nPPh2 (n=1 to 5) for the iodide ions in the parent octahedral hexarhenium cluster compound [Re6Se8I6]3-. The diphosphine Ph2P(CH2)nPPh2 ligands adopt an η1-bonding mode with the Re6(μ3-Se)8 core, and the P donor atom in the pendant arm is noncoordinated and oxygenated in most cases. The series of new hexarhenium(III) complexes have been well-defined by 1H, 13C, and 31P NMR spectroscopic and FAB-MS data. Four compounds among the series were characterized by X-ray structural determination. Geometrical isomers were identified by NMR spectroscopy as well as by the structural determinations. The apical ligand substitution induces significant change in the redox potentials and the photophysical properties of the Re6(μ3-Se)8 core. The E1/2 value of the reversible process ReIII6/ReIII5ReIV becomes more positive with the increasing number of the coordinated P donors. The phosphine-substituted hexarhenium(III) derivatives are highly luminescent, with microsecond scale emissive lifetime at ambient temperature, and the fully substituted derivatives with the formula [Re6Se8(η1 -diphosO)6]2+ display the strongest luminescence with the longest emission lifetimes.

Ru(bpy)2(CE-bpy)2+ was prepared where bpy and CE-bpy were 2,2′-bipyridine and bpy having a crown-ether moiety at the 3,3′ positions, respectively. Although the Ru(II) complex showed only very weak emission in acetonitrile, recognition of Na+ or Li+ by the crown-ether moiety in CE-bpy resulted in an increase in the emission intensity of the complex.

A terminal ligand-substitution reaction at triruthenium redox centres within monolayer films is investigated. For this purpose, a new redox-active trinuclear ruthenium complex containing one carbonyl ligand at a terminal site, [Ru3(O)(CH3COO)6(CO)(mpy)(C10PY)](mpy = 4-methylpyridine, C10PY = {(NC5H4)CH2NHC(O)(CH2) 10S-}2)1, has been chemically adsorbed onto a gold electrode surface with a disulfide-alkyl spacer C10PY. Densely packed monolayers of complex 1 on Au electrodes (surface coverage, Γ(Ru3) = 1.8 × 10-10 mol cm-2) display the {RuII-CO}RuIIIRuIII/{RuIII-CO}Ru IIIRuIII couple at E1/2 = +0.61 V vs. Ag-AgCl in a 0.1 mol dm-3 HClO4 aqueous solution. Upon electrochemical oxidation of the adsorbed complex at +0.80 V, where the triruthenium carbonyl complex is in the oxidized form {RuIII-CO}RuIIIRuIII, the coordinated CO is replaced by an aqua ligand present in the bulk phase, which is followed by cyclic voltammetry at appropriate electrolysis time intervals. During 8000 s of electrolysis, ca. 67% of the initially assembled carbonyl complexes are converted to the triruthenium aqua complexes, while ca. 25% desorbed from the electrode surface.

A reaction of trans-[(Cp*Rh)2(μ-CH2)2Cl2] with H2Se in MeOH formed a μ-SeH complex isolated as a BPh4 salt [(Cp*Rh)2(μ-CH2)2(μ-SeH)](BPh 4) (1; Cp* = η5-C5Me5). In solution, complex 1 was oxidized by molecular oxygen giving a tetranuclear diselenide μ4-Se2 complex [{(Cp*Rh)2(μ-CH2)2} 2(μ4-Se2)](BPh4)2 (2). The structure involves Se2 bridging two Rh-Rh bonds (Rh-Rh = 2.6353(5) Å) in a side-on fashion (Rh(1)-Se(1) = 2.4715(6), Rh(2)-Se(1)* = 2.5526(6) Å). The Se(1)-Se(1)* distance is 2.3875(9) Å, which corresponds to a Se-Se single bond. Complex 2 showed an intriguing dynamic behavior of double-site atomic inversion at the selenium atoms in CD3CN. The line shape analyses of the temperature dependent 1H-NMR spectra of the μ-CH2 groups elucidated the dynamic process and provided the activation parameters: ΔH‡ = 70 ± 1 kJ mol-1, ΔS‡ = 15 ± 5 J mol-1 K-1, and ΔG‡ = 66 ± 1 kJ mol-1 (at 298 K). © 2000 Elsevier Science S.A. All rights reserved.

New oxo-centred acetate-bridged triruthenium(in) complexes with a long alkyl-chain disulfide ligand, (NC5C5)CH2NHC(O)(CH2)SS(CH 2)C(O)NHCH2(C5C5N) (C5C5N represents a 4-pyridyl residue, n = 10; abbreviated as C10PY), have been prepared as a redox-active metal cluster adsorbate on gold electrodes: [Ru3(O)(CH3CO2)6(mpy)2(C10PY)]C1O4 5a (mpy = 4-methylpyridine), [Ru3(O)(CH3CO2)6(mpy)2(C10PY)]CF3SO3 5b. The preparation, spectroscopic and electrochemical properties of 5a,5b are presented and are compared with those of triruthenium(ni) analogues of a shorter alkyl-chain disulfide ligand (11 = 2; abbreviated as C2PY), eg. [Ru3(O)(CH3CO2)6(mpy)2(C2PY)]- C1O4 3a and [Ru3(O)(CH3CO2)6(MeIm) 2(C2PY)]ClO4 4a (Melm = 1-methylimidazole). Characterization of all the compounds was accomplished using 'H and 'H-'H COSY NMR, UV-vis and infrared spectroscopy, elemental analysis, fast-atom bombardment (FAB) mass spectrometry and cyclic voltammetry. Compounds 3a, 4a and 5a,5b in 0.1 M [;i-Bu4N]PF6-CH3CN exhibit three (Ru3(O)} cluster core-based one-electron redox waves which are all reversible in the applied potential range between +1.2 and -2.0 V vs. Ag-AgCl. The redox potentials are dependent on the basicity of the terminal ligands (mpy and Melm), but are insensitive to the length of the méthylène chains of the disulfide ligand (C10PY and C2PY). Self-assembly of 5b on a gold electrode results in the formation of electrochemically stable monolayers which exhibit one-electron redox wave corresponding to the Ru3 redox process III,IH,III-II,III,III in aqueous media containing 0.1 M supporting electrolytes. The redox potentials and the shape of the voltammetric waves of the surface-attached triruthenium complexes are found to be largely dependent upon the nature of anions used (ClO4-, CF3SO3-, NO3-, PF6- and SO42-) and also upon the basicity of terminal ligands on the (Ru3(O)} cluster moiety. © The Royal Society of Chemistry 2000.

Kinetics of the outer-sphere reduction reactions of [Fe(1,10-phenanthroline)(3)](3+) by two oxo-bridged ruthenium complexes, [Ru-3(mu (3)-O)(mu -CH3COO)(6)(pyridine)(3)](+) and [Ru-2(mu -O)(mu -CH3COO)(2)(pyridine)(6)](2+) have been studied using the stopped-flow technique in acetonitrile (I=0.005 and 0.001 M, respectively (NaClO4); 20-35 degreesC). Second-order rate constants at 25 degreesC (M(-1)s(-1)) activation enthalpy (DeltaH(double dagger)/kJ mol(-1)), and activation entropy (DeltaS(double dagger)/J K(-1)mol(-1)), are 2.05 x 10(6), 19 +/- 2, and -60 +/- 4, respectively, for the trimer, and 1.14 x 10(6), 8.8 +/- 0.8, and -100 +/- 3, respectively, for the dimer. The difference in kinetic parameters have been discussed in terms of smaller reorganization energy for the trimer. Emission quenching rate constants of [Ru(2,2'-bipyridine)(3)](2+) by seven ore-bridged di- and trinuclear ruthenium complexes including the above two complexes and [Ru2Rh(mu (3)-O)(mu -CH3COO)(6)(pyridine)(3)]+ and [Rh-3(mu (3)-O)(mu -CH3COO)(6)(pyridine)(3)](+), have been obtained in acetonitrile and DMF (0.1 M (n-C4H9)(4)N(ClO4)) at 22 degreesC. They are in the range of (1.17 - 3.95) x 10(9) M(-1)s(-1) except for the trirhodium complex which does not quench at all, and are independent of the redox potentials of the quenchers, thus suggesting an energy transfer mechanism.

New oxo-centred acetate-bridged triruthenium(III) complexes with a long alkyl-chain disulfide ligand, (NC5H4)CH2NHC(O)(CH2)(n)SS(CH2)(n)C(O)NHCH2(C5H4N) (C5H4N represents a 4-pyridyl residue, n=10; abbreviated as C10PY), have been prepared as a redox-active metal cluster adsorbate on gold electrodes: [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C10PY)]ClO4 5a (mpy=4-methylpyridine), [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C10PY)]CF3SO3 5b. The preparation, spectroscopic and electrochemical properties of 5a,5b are presented and are compared with those of triruthenium(III) analogues of a shorter alkyl-chain disulfide ligand (n=2; abbreviated as C2PY), e.g. [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C2PY)]ClO4 3a and [Ru-3(O)(CH3CO2)(6)(MeIm)(2)(C2PY)]ClO4 4a (MeIm=1-methylimidazole). Characterization of all the compounds was accomplished using H-1 and H-1-H-1 COSY NMR, UV-vis and infrared spectroscopy, elemental analysis, fast-atom bombardment (FAB) mass spectrometry and cyclic voltammetry. Compounds 3a, 4a and 5a,5b in 0.1 M [n-Bu4N]PF6-CH3CN exhibit three {Ru-3(O)} cluster core-based one-electron redox waves which are all reversible in the applied potential range between +1.2 and -2.0 V vs. Ag-AgCl. The redox potentials are dependent on the basicity of the terminal ligands (mpy and MeIm), but are insensitive to the length of the methylene chains of the disulfide ligand (C10PY and C2PY). Self-assembly of 5b on a gold electrode results in the formation of electrochemically stable monolayers which exhibit one-electron redox wave corresponding to the Ru-3 redox process III,III,III-II,III,III in aqueous media containing 0.1 M supporting electrolytes. The redox potentials and the shape of the voltammetric waves of the surface-attached triruthenium complexes are found to be largely dependent upon the nature of anions used (ClO4-, CF3SO3-, NO3-, PF6- and SO42-) and also upon the basicity of terminal ligands on the {Ru-3(O)} cluster moiety.

A dinuclear ruthenium complex [Ru2(dhpta)(μ-O2CCH3)2] - (H5dhpta = 1,3-diamino-2-hydroxypropane-N, N, N', N'-tetraacetic acid) is accumulated on a gold surface by using the ligand substitution reaction of bridging acetate in the complex by terminal benzoate in a self-assembled monolayer with 4-(6-mercaptohexoxy)benzoic acid. The accumulated complex, which shows a surface redox couple corresponding to Ru111Ru111/Ru111Ru11, covers the gold surface completely. The ligand substitution reaction is applicable for the accumulation of other complexes and useful for the designing of functional electrodes.

Novel self-assembled monolayers of a mixed-valent (μ3-oxo)triruthenium(II,III,III) complex containing a terminal CO ligand were constructed on Au(111) electrode surface and were characterized by cyclic voltammetry and in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). A distinctive infrared v(CO) absorption band was observed at 1950 cm-1 for the original {Ru11-CO}Ru111Ru111 complex in an aqueous 0.1 M NaClO4 solution and it shifted to 2060 cm-1 upon one-electron oxidation of the Ru11 center.

Novel self-assembled monolayers of oxide and acetate-bridged triruthenium(III) complexes have been prepared on Au(111) electrode surface. Parent discrete triruthenium(III) complexes with a terminal disulfide ligand, [Ru3(μ3-O)(μ-CH3CO2)6(L)2 (C2PY)]ClO4, where C2PY = {NC5H4CH2NHC(O)(CH2)2S-}2, L = 4-methylpyridine (mpy, 4a) and 1-methylimidazole (MeIm, 4b), were isolated through multistep synthesis. Complex 4a exhibits three reversible redox waves, while complex 4b exhibits two reversible and one irreversible redox waves in (n-C4H9)4NPF6/CH3CN, all ascribed to one-electron redox of the triruthenium cluster core. In aqueous solution containing a 0.1 M supporting electrolyte (NaClO4 or Na2SO4), self-assembled monolayers of 4a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru3(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru3 cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes.

Novel self-assembled monolayers of oxide and acetate-bridged triruthenium(III) complexes have been prepared on Au(111) electrode surface. Parent discrete triruthenium(III) complexes with a terminal disulfide ligand, [Ru-3(mu(3)-O)(mu- CH3CO2)(6)(L)(2)(C2PY)]ClO4, where C2PY = {NC5H4CH2NHC(O)(CH2)(2)S-}(2), L = 4-methylpyridine (mpy, 4a) and 1-methylimidazole (MeIm, 4b), were isolated through multistep synthesis. Complex 4a exhibits three reversible redox waves, while complex 4b exhibits two reversible and one irreversible redox waves in (n-C4H9)(4)NPF6/CH3CN, all ascribed to one-electron redox of the triruthenium cluster core. In aqueous solution containing a 0.1 M supporting electrolyte (NaClO4 or Na2SO4), self-assembled monolayers of 3a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru,(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru, cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes. (C) 1999 Elsevier Science S.A. All rights reserved.

A new series of linear-type Mo2Rh2 tetranuclear complexes, [{Cp*Rh(III)(μ-SCH3)3Mo(VI) O2}2(μ-O)] (1), [{Cp*Rh(III)(μ- SCH3)3Mo(V) O}2(μ-O)2] (2), and [{Cp*Rh(III)(μ-SCH3)3Mo(V) O}2(μ-O)(μ-S)] (3), has been prepared from reactions of the triple cubane-type oxide cluster [(Cp*Rh)4Mo4O16] · 2H2O with CH3SH. These tetranuclear complexes have been characterized by elemental analysis, infrared, electronic, and 1H, 13C, and 17O NMR spectroscopies as well as X-ray analysis. Complex 1 crystallizes in the monoclinic space group P21/n (No. 14) with a = 15.348(3), b = 14.059(3), c = 17.879(3) Å, β = 107.11(2)°, V = 3690(1) Å3, and Z = 4. Complex 2 crystallizes in the monoclinic space group C2/c (No. 15) with a = 25.334(4), b = 21.271(2), c = 17.831(3) Å, β = 129.70(5)°, V = 7393(2) Å3 and Z = 8. Complex 3 crystallizes in the orthorhombic space group Pcab (No. 61) with a = 16.902(3), b = 26.631(3), c = 16.855(2) Å, V = 7587(3) Å3, and Z = 8. Complex 1 involves a nearly linear 'O2Mo (VI)(μ-O)Mo(VI)O2' framework, to which two Cp*Rh(III) units are linked by μ-SCH3 ligands. Complexes 2 and 3 have an analogous tetranuclear Mo(V)/2Rh(III)/2 structure in which the Mo(V) and Rh(III) atoms are bridged by three μ-SCH3 ligands. Complex 2 contains a doubly-bridged 'OMo(V)(μ-O)2Mo(V)O' framework with an Mo-Mo distance of 2.564(1) Å, while 3 contains a 'OMo(V)(μ-O)(μ-S)Mo(V)O' framework with an Mo-Mo distance of 2.666(1) Å. Complexes 2 and 3 retain the tetranuclear structure but are fluxional in solution. The fluxional behaviors are due to intramolecular rotations of the 'Cp*Rh(μ-SCH3)' moieties on the trigonal planes of the octahedral Mo centers. Lineshape analyses of variable- temperature 1HNMR spectra measured in C6D5Cl yield activation parameters of ΔH(+), = +80.2 kJ mol-1, ΔS(+) = +22.1 J K-1 mol-1, and ΔG(298 K)/(+) = +73.6 kJ mol-1 for the rotation in 2 and ΔH(+) = +76.8 kJ mol-1, ΔS(+) = + 21.1 J K-1 mol-1, and ΔG(298 K)/(+) = + 70.5 kJ mol-1 for that in 3.

A series of side-on peroxide-bridged binuclear copper complexes [Cu2(NnPY2)(O2)]2+ (where n = 3-5), which have been proposed to adopt a butterfly Cu2O2 geometry due to the constraints placed on the Cu-Cu distance by the alkyl chain linker of length -(CH2)(n)- have been studied using absorption and resonance Raman spectroscopy and theoretical techniques. The four components of the peroxide to copper(II) charge-transfer transitions have been identified for the first time in the [Cu2(NnPY2)(O2)]2+ (where n = 3-5) complexes. The observed shift of the peroxide O-O stretch by 25 cm-1 to higher energy and the changes observed in the energy and intensity of absorption bands including the presence of an additional band at 23 800-20 400 cm-1 (420-490 nm) (not seen in planar side-on peroxide-bridged dicopper cores) are correlated to the butterfly structure using transition dipole vector coupling and valence bond configuration interaction models. The identification of an absorption band at 23 800-20 400 cm-1 (420-490 nm) associated with the butterfly side-on peroxide-bridged dicopper core is important since the isomeric, bis(μ-oxo) core is also characterized by an absorption band in this region. The changes in bonding associated with a butterfly distortion of the Cu2O2 core are defined, and the reactivity of the butterfly core with respect to electrophilic aromatic substitution and H atom abstraction reactions is compared with that of the planar side-on peroxide-bridged dicopper core using the frontier molecular orbital description.

The Mo(0) and Mo(VI) complexes of tris(2-pyridylmethyl)amine (tpa), Mo(CO)3(tpa) and Mo(O)3(tpa)·H2O, were synthesized. Structural analyses revealed tridentate coordination of tpa in both compounds. The fluxional behavior of both species was investigated by variable-temperature 'HNMR spectroscopy.

Self-assembled monolayers (SAMs) of non-heme diiron(III) biomimetic complexes have been prepared on Au(111) electrode surfaces to explore redox properties of diiron centers in aqueous solution in a wide pH range. The diiron(III) SAMs exhibited the proton-coupled electron-transfer reaction (1H+/le) in water.

A reaction of the triple cubane-type organometallic polyoxomolybdate cluster, [(Cp * Rh)4Mo4O16] · 2H2O (1 · 2H2O), with 1,2-benzenedithiol gives a 1,2-benzenedithiolate-bridged dinuclear complex, [(Cp * Rh)2(μ(S)-1,2-C6H4S2-S,S′)2] (2), and another dinuclear complex, [(Cp * Rh)2(μ(S)-1,2-C6H4S2-S,S′)(μ(S)-1,2-C6H4S(SO2)-S,S′)] (3), both of which are characterized by the single-crystal X-ray diffraction method. The former complex, 2, is also obtained from a reaction of [(Cp * RhCl)2(μ-Cl)2] with 1,2-benzenedithiol in the presence of NaOCH3, and the latter, 3, from oxygenation of 2 with t-BuOOH. The 1H NMR study in CD2Cl2 indicates that complex 2 changes gradually to a coordinatively unsaturated mononuclear complex, [Cp * Rh(1,2-C6H4S2-S,S′)] (4). An analogous mononuclear iridium(III) complex, [Cp * Ir(1,2-C6H4S2-S,S′)] (5), is also prepared and characterized by X-ray structural analysis. © 1997 Elsevier Science S.A.