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Effects of heteroatoms on electronic states of divana-dium-substituted γ-Keggin-type polyoxometalates (TBA)4[γ-XV2W10O38(µ-OH)(µ-OR)] (X = Ge, Si; R = Me, Et, n-Pr, H; TBA = tetra(n-butyl)ammonium) and (TBA)4[γ-XV2W10O38(µ-O)] (X = Ge, Si) were investigated, using a combination of nuclear magnetic resonance spectroscopy and density functional theory (DFT) calculations. Both the substitution of SiO4 heteroatom units with larger GeO4 ones and the introduction of more electronegative alkoxo groups in place of hydroxo groups resulted in deshielding of the vanadium nuclei. DFT calculations using the Def2-SVP basis set at TPSSh level of theory could well-reproduce the anionic moieties of a series of divanadiurn-substituted γ-Keggin-type polyoxometalates, and the estimated chemical shifts approximately reproduced the experimental ones with the individual gauge localized orbital method (SO-IGLO) taking the spin--orbit interaction into account. The magnetic shielding (σ) consists of σd + σp + σSD + σFC where σd σp, σSD, and σFC are diamagnetic, paramagnetic, spin-dipolar, and Fermi contact terms, respectively. The σp changed much among (TBA)4[γ-XV2W10O38(µ-OH)2], (TBA)4[γ-XV2W10O38(µ-OH)(µ-OR)], and (TBA)4[γ-XV2W10O38(µ-O)], while σd, σSD, and σFC did not change much. Therefore, the σp largely contributed to the magnetic shielding. Moreover, σp consisted of the occupied--occupied transitions (s-terms) and the occupied--virtual ones (u-terms), and the u-terms were predominant for σp. The most contributing occupied localized orbital consisted of the dz² orbital of vanadium, the p. orbital of terminal oxygen related to the V=O bond, and the pz orbital of oxygen of the XO4 unit, whereas the two virtual localized orbitals consisted of the dyz orbital of vanadium and the py orbital of terminal oxygen. Analysis of the structural and electronic characteristics of a series of divanadium-substituted γ-Keggin-type POMs revealed a linear correlation between both 51V{H} chemical shifts and the reciprocal values of the energy gaps between the corresponding XO4-predominant orbital HOMOs-X and the LUMOs+X (X = 0, 1, or 2). All these results indicate that neighboring XO4 units weakly interact with the addenda atoms and control the electronic states of polyoxometalates and the magnetic shielding of their addenda atoms. [ABSTRACT FROM AUTHOR]

A spatial division (SD) transmission method utilizing the characteristics of two-ray fading due to ground reflection with linear antenna arrays horizontal to the ground is proposed. Formulations of the optimum array arrangements as functions of the transmission distance and achievable channel capacity are clarified. For two- and three-element arrays, channel capacity is respectively doubled and tripled over that of free-space propagation. The proposed method provides increased capacity without the extra signal processing cost incurred when using conventional multiple- input-multiple-output (MIMO) transmission. [ABSTRACT FROM AUTHOR]

Structural control among hexagonal (trimer), rhomboidal (dimer), and infinite-chain supramolecular complexes with three different supporting ligands of ethylenediamine (en), N,N,N',N'-tetramethylethylenediamine (en*), and 1,2-bis(diphenyl)phosphinoethane (dppe) [(en)Pd(L)]3(OTf)6 1t·OTf, [(en*)Pd(L)]2(PF6)4 2d·PF6, and [(dppe)Pd(L)(OTf)2]00 3·OTf (OTf = trifluoromethane sulfonate; L = 1,3-bis(4-pyridylethynyl)benzene) in the solid and solution states was investigated. The encapsulation of a large Keggin-type polyoxometalate [α-PW12O40]3- by these complexes was also examined. As the steric bulkiness of the supporting ligands increased in the order of en < en* < dppe, the hexagonal, rhomboidal, and infinite-chain structures were obtained, as confirmed by X-ray crystallography. In solution, equilibrium between the molecular hexagon (1t·OTf/2t·PF6) and the molecular rhomboid (1d·OTf/2d·PF6) was observed in the en/en* ligand systems, whereas 3·OTf with the dppe ligand did not exhibit equilibrium and instead existed as a single species. These phenomena were established by cold-spray ionization mass spectroscopy (CSI-MS) and 1H diffusion ordered NMR spectroscopy (DOSY). The addition of the highly negatively charged Keggin-type phosphododecatungstate [α-PW12O40]3- to a solution of 2t/2d·PF6 resulted in the encapsulation of the tungstate species in the cavity of the molecular hexagon to form {[(en*)Pd(L)]3[α-PW12O40]}(PF6)3 2t·[α-PW12O40]3-, as confirmed by a combination of 1H and 31P DOSY and CSI-MS spectral data. [ABSTRACT FROM AUTHOR]

Effects of isolobal heteroatoms in divanadium-substituted γ- Keggin-type polyoxometalates, (TBA)4[γ-XV2W10O38(μ-OH)2] IX and (TBA)4[γ-XV2W10O38(μ-O)] 2X (where X = Ge or Si), on (OV)2(μ-OH)2 and (OV)2(μ-O} core structures and transformations from 2X to 1x have been investigated. X-ray crystallography of 1x and 2X reveals that larger Ge (covalent radius 1.22 Å; covalent radius of Si 1.11 Á) induces (a) expansion of (OV)2(μ-OH)2 and (OV)2(μ-O) cores, (b) expansion of lacunary sites, and (c) deep location of divanadium cores inside their lacunary sites. Density functional theory (DFT) calculations for anionic moieties of 1x and 2X reveal that energy levels of the highest occupied molecular orbital (HOMO)--1 in 1Ge and HOMO in 2Ge are lower than those in 1Si and 2Si, respectively, because of smaller contribution of pz orbitals of oxygen atoms in 1Ge and 2Ge, which would result from shorter V┅O(--Ge) distances. Compound 2Ge reacts with water vapor to form (TBA)4[γ-GeV2W10O38(μ-OH)2] 1'Ge via a crystal-to-crystal transformation, and the water dissociation proceeds heterolytically. DFT calculations reveal that the reaction proceeds through (1) coordination of water on a coordinatively unsaturated site of vanadium in the lowest unoccupied molecular orbital (LUMO), followed by (2) proton transfer to the bridging oxo moiety. The order is different from that in 2Si, which would result from the lower energy level of HOMO of 2Ge (i.e., lower nudeophilicity toward a proton of water) than that of 2Si. [ABSTRACT FROM AUTHOR]

The reactivity of divanadium-substituted silicotungstate, γ-H2SiV2W10O404- (I), with hydroxo compounds of alcohols, carboxylic acids, and water is reported. The reaction of the bis(μ-hydroxo) divanadium site in I with primary alcohols and formic acid smoothly proceeds to form corresponding monoesters and monoformate, respectively, and the crystal structures of the monomethyl and monoethyl esters and the monoformate of I are determined. The oxygen exchange between the hydroxo group and water proceeds easily. On the other hand, bulky compounds of 2-propanol, tert-butyl alcohol, and acetic acid hardly react with the bis(μ-hydroxo) divanadium site (equilibrium constant « 0.01) because of the steric crowding between the methyl groups and the polyoxometalate framework. [ABSTRACT FROM AUTHOR]