Studies in Mössbauer spectroscopy. Part IV. Signs of the quadrupole coupling constants for some organotin(IV) compounds

Abstract

Mössbauer spectra of some four-, five-, and six-co-ordinate organotin(IV) compounds, covering seven different structural types, have been measured in an applied magnetic field. From the signs of the quadrupole coupling constants, it is shown that the electric field gradient at the tin nucleus arises primarily from differences in the electron densities of the tin–ligand bonds (i.e.|q_val| > |q_lat|). The relative signs of the coupling constants agree with those predicted for regular structures by the point-charge model, except for the cis-R₂SnX₄ complexes. The apparently anomalous sign for the latter is probably due to deviations from strict octahedral geometry. It is deduced that the field gradient is largely determined by the disposition of the tin–carbon bonds.