Yoshiki Ozawa

Abstract The title complex was newly synthesized by straightforward ligand substitution of a parent complex having a N2P2 set. The present complex had a deformed rhomboidal {Cu2I2} core with shortened Cu···Cu and prolonged I···I diagonals compared with those of the parent complex and formed one-dimensional channels filled with solvent molecules in crystals. The complex exhibited unusual red shift in solid-state photoluminescence assigned to halogen/metal-to-ligand charge transfer, indicating association of the unique crystal packing containing intramolecular electronic coupling between benzothienobenzothiophene moieties.

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.

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.

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.

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.

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.

The structure of a hexanuclear silver(I) complex with six quinoline-2-thiolato (2-qnt(-)) ligands [Ag-6(C9H6NS)(6)] (1) has been synthesized and characterized. Complex 1 crystallized in a triclinic space group P-1 (No. 2) with a = 8.064(6), b = 13.480(3), c = 13.573(5) angstrom, alpha = 113.528(15)degrees, beta = 104.24(3)degrees, gamma = 100.46(3)degrees, V = 1244.5(11) angstrom(3), Z = 1, T = 150 K. The R1 [I > 2 sigma(I)] and wR2(all data) values are 0.032 and 0.089, respectively, for all 4437 independent reflections. The complex has a paddle-wheel-like structure with a trigonally distorted Ag6 octahedral metal core.

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.

Three oligomeric arylstibonates [H-5(p-ClC6H4Sb)(16)O-36](3-), [H-4(p-ClC(6)H(4)Sh)(16)O-36](4-), and [Na-2(p-ClC6H4Sb)(12)O-24(OH)(6)(H2O)(3)](4-) have been synthesized as tetra-n-butylammonium salts and structurally characterized. The Sb16C16O36 core of the [H-5(p-ClC6H4Sb)(16)O-36](3-) and [H-4(p-ClC6H4Sb)(16)O-36](4-) anions is made up from arrays of close-packed O and C atoms and Sb atoms that occupy the octahedral interstices between the close-packed layers. The layers of close-packed O and C atoms are stacked in a sequence ABACA, resulting in an hch packing. The [Na-2(p-ClC6H4Sb)(12)O-24(OH)(6)(H2O)(3)](4-) anion has an "opened-up" delta-Keggin structure.

Two new one-dimensional (1D) rhodium(I)-semiquinonato complexes formulated as [Rh(3,6-DBSQ-4,5-PDO)(CO)(2)](infinity) (4; 3,6-DBSQ-4,5-PDO center dot- = 3,6-di-tert-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh(3,6-DBSQ-4,5-(N,N'-DEN))(CO)(2)](infinity) (5; 3,6-DBSQ-4,5-(N,N'-DEN)(center dot-) = 3,6-di-tert-butyl-4,5-(N,N'-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh(3,6-DBSQ-4,5-(MeO)(2))(CO)(2)](infinity) (3; 3,6-DBSQ-4,5-(MeO)(2)(center dot-) = 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds 4 and 5 comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh-Rh distances of 3.06 angstrom for 4 and 3.10 angstrom for 5. These distances are similar to those for 3 (3.09 angstrom); however, the molecules of 5 are strongly dimerized in the 1D chain. Compound 4 undergoes a first-order phase transition at Ttrs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound 4 exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at TN = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (E-a = 31 meV) in the RT phase to a semiconductor with a large activation energy (E-a = 199 meV) in the LT phase. These behaviors are commonly observed for 3. Alternating current susceptibility measurements of 4, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for 3, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound 5, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 x 10(7) Omega cm.

A tetra-n-butylammonium (TBA) salt of [Ta10O28](6-) was synthesized by heating TBA(6)[H2Ta6O19] in toluene for a prolonged period. X-ray structural analysis of TBA(6)[Ta10O28]center dot 6H(2)O revealed that the anion has the decametalate structure and is isostructural with the decavanadate and decaniobate anions [a = 15.8517(8) angstrom, b = 19.364(1) angstrom, c = 21.935(1) angstrom, beta = 93.638(1)degrees, V = 6719.4(6) angstrom(3), Z = 2, and space group P2(1)/n at 292(2) K].

A new one-dimensional platinum mixed-valence complex with nonhalogen bridging ligands, namely catena-poly[[[bis(ethane-1,2-diamine-kappa N-2,N')platinum(II)]-mu-thiocyanato-kappa S-2:S-[bis(ethane-1,2-diamine-kappa N-2,N')platinum(IV)]-mu-thiocyanato-kappa S-2:S] tetrakis(perchlorate)], {[Pt-2(SCN)(2)(C2H8N2)(4)](ClO4)(4)}(n), has been isolated. The Pt-II and Pt-IV atoms are located on centres of inversion and are stacked alternately, linked by the S atoms of the thiocyanate ligands, forming an infinite one-dimensional chain. The Pt-IV-S and Pt-II center dot center dot center dot S distances are 2.3933 (10) and 3.4705 (10) angstrom, respectively, and the Pt-IV-S center dot center dot center dot Pt-II angle is 171.97 (4)degrees. The introduction of nonhalogen atoms as bridging ligands in this complex extends the chemical modifications possible for controlling the amplitude of the charge-density wave (CDW) state in one-dimensional mixed-valence complexes. The structure of a discrete Pt-IV thiocyanate compound, bis(ethane-1,2-diamine-kappa N-2,N')bis(thiocyanato-kappa S)platinum(IV) bis(perchlorate) 1.5-hydrate, [Pt(SCN)(2)(C4H8N2)(2)](ClO4)(2)center dot 1.5H(2)O, has monoclinic (C2) symmetry. Two S-bound thiocyanate ligands are located in trans positions, with an S-Pt-S angle of 177.56 (3)degrees.

The structural phase transitions of phosphorus (P) were investigated at pressures up to 340 GPa by a synchrotron radiation x-ray powder diffraction technique at room temperature. The transition from the simple hexagonal P-V to the P-VI phases was confirmed at 262 GPa. The results of full-profile Rietveld refinements indicate that the structure of the P-VI phase is a 2x2x2 superlattice of the bcc structure [cI16 (space group: I-43d)], which is isotypic to high-pressure phases of Li and Na. This phase was found to be stable up to 340 GPa. The results have demonstrated the extension of structure refinement to a complex high-pressure phase above 300 GPa by the x-ray diffraction method.

Two vanadoperiodates of the decavanadate structure, [IV9O28](4-) and [HIV9O28](3-), have been synthesized and structurally characterized. The I atom replaces only the central V atom of [V10O28](6-) in [HIV9O28](3-), while replacement at both central and capping sites is observed for [IV9O28](4-). The proton in [HIV9O28](3-) is probably attached to one of the oxygen atoms that bridges two V atoms. The [HIV9O28](3-) anion is structurally very similar to [HTeV9O28](4-). This structural similarity is reminiscent of that observed between the Anderson-type molybdotellurate and molybdoperiodate, [TeMo6O24](6-) and [IMo6O24](5-). (c) 2012 Elsevier Ltd. All rights reserved.

A tetra-n-butylammonium (TBA) salt of [H-4.5(Ta6O19)](3.5-) was synthesized by reacting hydrous tantalum oxide with TBAOH. X-ray structural analysis of TBA(3.5)[H-4.5(Ta6O19)]center dot 2THF center dot 5.5H(2)O (THF = tetrahydrofuran) revealed that this compound consists of a hydrogen-bonded, rod-shaped tetramer of hexatantalate that is almost 30 angstrom long together with TBA cations and solvent molecules of crystallization [a = 20.6354(5) angstrom, b = 25.5951(7) angstrom, c = 37.2058(8) angstrom, alpha = 77.092(1)degrees, beta = 86.177(1)degrees, gamma = 88.683(1)degrees, V = 19110.9(8) angstrom(3), Z = 8, and space group P (1) over bar]. H-1 NMR spectra showed that this tetrameric structure is maintained in solution.

A tetra-n-butylammonium (TBA) salt of [H-4.5(Ta6O19)](3.5-) was synthesized by reacting hydrous tantalum oxide with TBAOH. X-ray structural analysis of TBA(3.5)[H-4.5(Ta6O19)]center dot 2THF center dot 5.5H(2)O (THF = tetrahydrofuran) revealed that this compound consists of a hydrogen-bonded, rod-shaped tetramer of hexatantalate that is almost 30 angstrom long together with TBA cations and solvent molecules of crystallization [a = 20.6354(5) angstrom, b = 25.5951(7) angstrom, c = 37.2058(8) angstrom, alpha = 77.092(1)degrees, beta = 86.177(1)degrees, gamma = 88.683(1)degrees, V = 19110.9(8) angstrom(3), Z = 8, and space group P (1) over bar]. H-1 NMR spectra showed that this tetrameric structure is maintained in solution.

Treatment of an aqueous solution of dipicolinic acid (dipicH(2)) and 3-amino-1H-1,2,4-triazole (atr) with ZnCl2 or Ni(NO3)(2)center dot 6H(2)O (in a molar ratio of 1:1:1) led to the formation of co-crystals of (atrH)(2)[M(dipic)(2)]center dot[M(H2O)(6)][M(dipic)(2)]center dot 2H(2)O (M = Zn (1) and Ni (2)). Both complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. Their molecular and crystal structures were determined by Xray crystal structure analysis and their thermal stability was confirmed by TGA-DTA methods. The complexes 1 and 2 display isostructural features and crystallize in the triclinic P (1) over bar space group. The infrared spectra of 1 and 2 are very similar, so these complexes cannot be unambiguously distinguished by IR spectroscopy. Thermal methods confirm the number of co-crystallized water molecules in both compounds. Extensive hydrogen bonding interactions involving all aqua ligands, dipicolinate oxygen atoms and lattice water molecules further stabilize the complex units by linking them to form three dimensional polymeric networks. (C) 2011 Elsevier Ltd. All rights reserved.

Two new vanadotellurates, [HTeV9O28](4-) and [H2TeV9O28](3-) have been synthesized and structurally characterized as tetra-n-butylammonium (TBA) salts: TBA(4)-[HTeV9O28]center dot 2CH(3)CN [triclinic, space group P (1) over bar, a = 16.7102(6) angstrom, b = 17.4680(7) angstrom, c = 17.9634(7) angstrom, alpha = 74.412(1)degrees, beta = 67.494(1)degrees, gamma = 74.160(2)degrees, Z = 2] and TBA(3)-[H2TeV9O28] [monoclinic, space group P2(1)/c, a = 13.0013(5) angstrom, b = 19.157(1) angstrom, c = 28.453(1) angstrom, beta = 97.222(2)degrees, Z = 4]. The results of the structural analyses indicate that the four O atoms that bridge two V atoms on the Te side are the most basic ones in the structure. The results of density-functional theory (DFT) calculations support this view.

The first protonated hexatantalate, [H2Ta6O19](6-), has been synthesized and structurally characterized. X-ray diffraction analysis revealed that the protons are selectively attached to the O atoms that bridge two Ta atoms. The overall structure of the [H2Ta6O19](6-) anion is virtually identical to that predicted by a DFT calculation. (C) 2010 Elsevier B.V. All rights reserved.

The photoexcited charge-transferred state of [AuCl(PPh3)(2)] in a novel polymorphic crystal form was directly observed by X-ray photocrystallographic analysis. Its photoexcited state was completely different from the one generated in the known crystal of [AuCl(PPh3)(2)]; the photoexcited bond-shrunk state was generated in the known crystal. This difference in the generated photoexcited state was clearly reflected by the difference in emission color. While the known crystal form showed green phosphorescence, the novel form showed blue phosphorescence under UV irradiation. The difference in the generated photoexcited state was due to the differences in steric hindrance in the crystal; bond shortening by photoexcitation was sterically allowed in the known form, while on the other hand, it was restricted in the novel form. Therefore, instead of the bond-shrunk state, the charge-transferred excited state became the lowest triplet state, and the emission color changed from green to blue (i.e., a blue shift of the emission wavelength was observed). These results mean that the photoexcited structure and the emission color of [AuCl(PPh3)(2)] can be controlled by designing the molecular environment in the crystal.

Three different solvates of TBA(6)[Nb10O28] (TBA = tetra-n-butylammonium) were structurally characterized. The results revealed that two water molecules are hydrogen-bonded to the terminal oxygens of the [Nb10O28](6-) anion in the same manner in all of the solvates. Decaniobate [Nb10O28](6-) dimerizes by the action of HCl to form icosaniobate [Nb20O54](8-), while icosaniobate breaks up into decaniobate [Nb10O28](6-) by the action of TBAOH. Decaniobate also dimerizes spontaneously to form icosaniobate [Nb20O54](8-) in CH2Cl2 even if no acid is added to the solution. The reaction was followed by IR spectroscopy, and the results suggested the reaction is second order with respect to the concentration of [Nb10O28](6-). (C) 2010 Elsevier Ltd. All rights reserved.

Multitemperature X-ray structure analyses and photoemission spectra of [Cu4I4(PPh3)(4)] in two polymorphic crystals reveal that the cubane-like framework is flexibly distorted effecting luminescence thermochromism.