STRUCTURAL AND QUANTUM-CHEMICAL STUDY OF BI-5(3-GROUP METAL-CLUSTERS - THE CRYSTAL-STRUCTURE OF PENTABISMUTH(3+) TETRACHLOROGALLATE(III) REFINED FROM X-RAY-POWDER DIFFRACTION DATA AND SYNTHETIC ATTEMPTS ON ITSANTIMONY ANALOG() AND ISOELECTRONIC MAIN)

Pentabismuth(3+) tetrachlorogallate(III), (Bi-5(3+))(GaCL(4)(-))(3), h as been synthesized by reducing a BiCl3-GaCl3 melt with bismuth metal and the crystal structure refined from X-ray (Cu K alpha(1)) powder di ffraction data. The structure was found to belong to space group R-3c, with the lattice parameters a = 11:871(2) Angstrom and c = 30.101(3) Angstrom (Z 6). It is isostructural with the previously characterized Bi-5(AlCl4)(3). An attempt to synthesise the antimony analogue Sb-5(Ga Cl4)(3) by reducing a SbCl3-GaCl3 mixture with gallium metal produced a black solid phase. The gallium content of this phase is consistent w ith the stoichiometry Sb-5(GaCl4)3, and the Raman spectrum of the phas e dissolved in SbCl3-GaCl3 comprises strong, low-frequency bands attri butable to Sb-Sb stretch vibrations in Sb-5(3+) or another reduced ant imony species. Quantum chemical analyses have been performed for the i soelectronic, trigonal pyramidal close-clusters Sn-5(2-), Sb-5(3+), Tl -5(7-), Pb-5(2-), and Bi-5(3+), bath with extended Huckel (eH) and Har tree-Fock (I IF) methods. The HF calculations were performed with and without corrections for the local electron-electron correlation using second-order Moller-Plesset perturbation theory (MP2). All theoretical results are compared and evaluted with respect to experimental cluste r structures and vibrational frequencies. The results from the calcula tions agree well with available experimental data for the solid-state structures and vibrational spectra of these cluster ions, except for t he Tl-5(7-) ion. Isolated Tl-5(7-) is suggested to be electronically u nstable because of the high charge density. The Sb-5(3+) cluster ion i s indicated to be stable. According to the calculations, Sn-5(2-) and Pb-5(2-) may be described in terms of edge-localized bonds without sub stantial electron density between the equatorial atoms, whereas Sb-5(3 +) and Bi-5(3+) have electron density evenly distributed over all M-M vectors. Furthermore, the theoretical results give no support for a D- 3h --> C-4v fluxionality of these clusters.