The pH dependent nuclearity variation of {Mo(154-x)}-type polyoxomolybdates and tectonic effect on their aggregations

The pH dependence of the structures of {Mo(154-x)} mixed-valence oxomolybdate giant clusters were investigated by synchrotron X-ray diffraction of systematically prepared crystals containing [Mo138O410(OH)20(OH2)46](40-) (1), [Mo138O410(OH)20(OH2)38](40-) (2), [Mo138O406(OH)16(OH2)46](28-) (3), [Mo142O400(OH)52(OH2)38](28-) (4), [Mo142O432(OH2)58](40-) (5), [Mo148O436(OH)15(OH2)56](27-) (6), [Mo150O451(OH)5(OH2)61](35-) (7), and both [Mo150O442.5(OH)11.5(OH2)64](24.5-) and [Mo152O446(OH)20(OH2)54](28-) (8). Crystals 1, 4, and 5 contain discrete clusters while intercluster Mo-O-Mo bonds connect the clusters into chains in crystal 7, into two-dimensional networks in crystals 2 and 3, and into a three-dimensional framework structure in crystal 6. Crystal 8 contains both discrete and linearly catenated clusters: discrete {Mo150} are located between the chains of {Mo152}. Direct correlation was observed between the nuclearity of the clusters with the pH of the mother liquor. On the other hand, the geometries of extended structures do not show apparent correlation with the pH. They turned out to be governed by the tectonics of the component clusters. The pH of the mother liquor exerts influence on the extended structure through the structures of the constituent clusters.     

Synthesis of dendritic oligothiophenes and their self-association properties by intermolecular pi-pi interactions

[structure: see text] The addition of oligothiophene into a dendritic structure causes a self-association behavior by intermolecular pi-pi interactions in a solution and in a solid state. Increasing the generation of the dendritic structure gives not only a high association constant but also sufficient field-effect hole mobility, which indicates that the charge-transporting passes are formed by the strong pi-pi interactions.     

A hexagonal prismatic porphyrin array: synthesis, STM detection, and efficient energy hopping in near-infrared region

A belt-shaped hexagonal cyclic porphyrin array 2 that comprises of six meso-meso, beta-beta, beta-beta triply linked diporphyrins 3 bridged by 1,3-phenylene spacers is prepared by oxidation from cyclic dodecameric array 1 consisting of six meso-meso directly linked diporphyrins 4 with DDQ and Sc(OTf)3. The absorption spectrum of 2 is similar to that of the constituent subunit 3 but shows a slight red-shift for the Q-bands in near-infrared (NIR) region, indicating the exciton coupling between the neighboring diporphyrin chromophores. Observed total exciton coupling energies in the absorption spectra were largely matched with the calculated values based on point-dipole exciton coupling approximation. It was found that the experimental exciton coupling strength (292 cm(-1)) of the Q-band in 2 is slightly larger than the calculated one (99 cm(-1)), indicating that the electronic communications are enhanced through 1,3-phenylene linkers in hexameric macromolecule. A rate of the excitation energy hopping (EEH) that occurs in 2 at the lowest excited singlet state in the near-infrared region has been determined to be (1.8 ps)(-1) on the basis of the pump-power dependent femtosecond transient absorption (TA) and the transient absorption anisotropy (TAA) decay measurements. The 2 times faster EEH rate of 2 than that of 1 (4.0 ps)(-1) mainly comes from involving through-bond energy transfer among diporphyrin subunits via 1,3-phenylene bridges as well as F?rster-type through-space EEH processes. STM measurement of 2 in the Cu(100) surface revealed that it takes several discrete conformations with respect to the relative orientation of neighboring diporphyrins. Collectively, an effective EEH in the NIR region is realized in 2 due largely to the intensified oscillator strength in the S(1) state (Q-band) and the close proximity held by 1,3-phenylene spacers.     

Protonation and methylation of an Anderson-type polyoxoanion [IMo6O24]5-

A series of protonated and methylated Anderson-type molybdoperiodates as well as the unprotonated [IMo6O24]5- have been synthesized and structurally characterized as tetra-n-butylammonium salts: [(n-C4H9)4N]5[IMo6O24] [monoclinic, space group C2/c, a = 33.6101(3) A, b = 15.2575(1) A, c = 24.0294(2) A, beta = 126.9569(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OH)] [monoclinic, space group P21/c, a = 9.5587(1) A, b = 24.1364(2) A, c = 18.2788(2) A, beta = 90.1562(5) degrees , Z = 2], [(n-C4H9)4N]3[IMo6O22(OH)2].2DMF [monoclinic, space group P21/a, a = 17.6105(4) A, b = 15.5432(5) A, c = 29.3316(9) A, beta = 91.475(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OMe)].3H2O [orthorhombic, space group Pbca, a = 17.0679(4) A, b = 25.6998(6) A, c = 20.7428(4) A, Z = 4], [(n-C4H9)4N]3[IMo6O22(OMe)2] [monoclinic, space group P21/n, a = 10.4009(1) A, b = 14.6658(3) A, c = 23.5395(4) A, beta = 100.324(1) degrees , Z = 2]. In all of these compounds, the [IMo6O24]5- anion is protonated or methylated selectively at O atoms shared by two Mo atoms. The results have also revealed that the protonated Anderson-type molybdoperiodates readily react with methanol in a very selective manner, while the unprotonated [IMo6O24]5- anion does not react with methanol under similar conditions.     

Synthesis, single crystal X-ray analysis, and TEM for a single-sized Au11 cluster stabilized by SR ligands: The interface between molecules and particles

An SR-modified Au cluster with a sub-nanometer size, Au₁₁(S-4-NC₅H₄)₃(PPh₃)₇ (1), has been synthesized by NaBH₄ reduction of Au(S-py)(PPh₃) or by reacting [Au₉(PPh₃)₈](NO₃)₃ with HS-4-py in good yield. Its molecular structure has been elucidated by single crystal X-ray diffraction, and TEM observation has been achieved for the first time for this size of SR-modified Au clusters. The core structure is best described in terms of an incomplete icosahedron. CV measurements in CH₂Cl₂ have suggested that the cluster does not coagulate in solution with significant concentration.     

Tension–compression asymmetry of phosphor bronze for electronic parts and its effect on bending behavior

In-plane tension and compression experiments on copper alloy sheets (phosphor bronze) and 6000 series aluminum alloy sheets (AA6016-T4) were conducted using a specially designed testing apparatus. The apparatus is equipped with comb-type dies so that stress–strain curves of a sheet specimen subjected to tension followed by compression, and vice versa, can be measured without buckling of the specimen, as well as those for monotonic tension and compression. A difference was observed in the flow stresses between tension and compression for the as-received copper alloy, but not for the aluminum alloy. Moreover, stress reversal tests, such as tension followed by compression and compression followed by tension, were carried out in order to measure the Bauschinger effect. In the second part of the experiment, bending moment–curvature diagrams were measured for the as-received and pre-stretched specimens. The bending moment–curvature diagrams were compared with those calculated using the stress–strain curves obtained from the tension–compression tests, and were in good agreement with those calculated with the tension–compression asymmetry and the Bauschinger effect correctly reproduced.     

Synthesis and Structural Characterization of Isomers of Ru-Substituted Keggin-Type Germanotungstate with dmso Ligand

We found that three isomers of mono-Ru substituted Keggin-type germanotungstate with a dmso ligand, [GeW₁₁O₃₉Ru^II(dmso)]^6?, could be formed by a reaction of α-Keggin-type mono-lacunary germanotungstate, [α-GeW₁₁O₃₉]^8?, with Ru(dmso)₄Cl₂. The main isomer is an α-isomer, and the others are β₂-isomer and β₃-isomer, which were confirmed by ¹H NMR, cyclic voltammetry, IR, and single crystal X-ray structure analysis.