Studies in Mössbauer spectroscopy. Part 11. Antimony-121 spectra of some complexes of palladium(II) and platinum(II) with tertiary stibines

Abstract

Antimony-121 Mössbauer spectra have been obtained for 23 complexes of the type [MX₂L₂][L = SbPh₃, Sb(C₆H₄Me-p)₃, Sb(C₆H₄Me-o)₃, SbEt₃, or Sb(C₆H₁₁)₃; M = Pd or Pt; X = Cl, I, or NO₂], for the five-co-ordinate [Ptl₂L₃](L = SbMePh₂ or SbMe₂Ph), for [RhCl₃(SbPh₃)₃], and for the free triarylstibines. In each case co-ordination results in a large increase in isomer shift and a decrease in quadrupole coupling constant, as expected for substantial removal of electron density from the lone pair on the antimony atom. In conjunction with far-i.r. data, configurations are assigned to the square-planar complexes, which are cis unless the stibine is sterically demanding. The cis and trans influences of the halides on the electron density on the antimony atom are shown to be opposed.