The far-infrared and Raman spectra of the tetra-alkylammonium salts of mixed tetrahalogeno-complexes of arsenic(III), antimony(III), and bismuth(III), [R4N][MX3Y]

Abstract

The far-i.r. and Raman spectra are reported for tetra-alkylammonium salts of [MX₃Y]^– anions (X ≠ Y: M = As, X or Y = Cl or Br; M = Sb, X or Y = Cl, Br, or I; M = Bi, X or Y = Cl, Br, or I; excluding [BiBr₃Cl]^–). Except in the cases of [Et₄N][SbBr₃Cl] and [Buⁿ₄N][Sbl₃Br] in the solid state, the spectra are indicative of structures of C_s symmetry based on trigonal bipyramidal arrangements of electron pairs around the group VB element. For M = Sb or Bi, and X = Cl, either Y or the lone pair of electrons occupies an axial position, whereas for all the other [MX₃Y]^– species both axial sites are occupied by X atoms.