An antimony-121 Mössbauer spectroscopic study of some dihalogeno(halogen-substituted benzene-1,2-diolato)antimonate(III) complexes and of some tetrabromoantimonates(III)

Abstract

The ¹²¹Sb Mössbauer parameters are reported for a series of heterocyclic base salts of tetrabromoantimonate(III) and dihalogeno(halogen-substituted benzene-1,2-diolato)antimonate(III) anions. A close relationship is found between chemical isomer shifts (δ) and the number of short bonds fomed by Sb. It is shown that the shift is determined by the length of the shortest bonds and their number rather than by the total number of bonding interactions formed by the Sb^III in the highly distorted environments of the complexes. The larger negative shifts for the SbBr₄^– complexes compared with SbBr₃ is consistent with a decrease in the number of short Sb–Br bonds and hence in the covalent character of the Sb–Br interactions. The shift for the benzenediolatoantimonates(III) is shown to be dominated by the presence of two short Sb–O bonds. It is suggested that the size of the ¹²¹Sb quadrupole-coupling constant (eQV_zz) in these antimony(III) materials depends not only on the p-electron excess in the lone-pair orbital but also on the details of the use of Sb p electrons is bond formation.