Experimental and theoretical studies of the molecular and crystal structures of trialkoxy- and chlorodialkoxy-stibanes

摘要

The molecular structures of triisopropoxystibane, Sb(O~iPr)_3, and chlorodiisopropoxystibane, SbCl(O~iPr)_2, were determined in the solid state by single crystal X-ray diffraction. Sb(O~iPr)_3 forms discrete centrosymmetric dimers in the solid via Sb…O-Sb interactions, leading to pseudo trigonal bipyramidal configurations of the four co-ordinate Sb atoms, while SbCl(O~iPr)_2 forms chains vai Sb…O-Sb and Sb…Cl-Sb bridges, resulting in five-co-ordinate Sb atoms with pseudo octahedral configurations. Comparison of the solid state structures and the density functional optimized molecular structuresof Sb(Ome)_3, SbCl(O~iPr)_2 and their dimers revealed a steady increase of the average Sb-O bond lengths with the co-ordination number of Sb, and mutual trans effects of the ligands. Standard enthalpies of dimer formation from density functional calculations are -23.8 and -69.7 kJ/mol~(-1) for [Sb_2(#mu#-Ome)_2(Ome)_4] and [Sb_2Cl_2(#mu#-OMe)_2(Ome)_2], respectively, and -42.7 kJ/mol~(-1) for [Sb_2(#mu#-Cl)_2(Ome)_4] . A natural bond orbital analysis reveals that n(O)-#sigma#_*(Sb-O) and n(O)-#sigma#_* (Sb-Cl) interactions are the main contributions to the inter-monomer bonding in the O-bridged dimers, of Sb(Ome)_3 and SbCl(Ome)_2, respectively, while n(O)-#sigma#_*(Sb-O) plays no significant role in the Cl-bridged dimer of SbCl(Ome)_2. IR and Raman spectra of Sb(O~iPe)_3 indicated molecular association in the solid and liquid phase, but dissociation into monomers in non-polar solvents.