Systematics of Mössbauer Isomer Shifts of Organo-Tin Compounds

Abstract

The Mössbauer spectra of 49 organo-tin compounds have been studied at liquid-nitrogen absorber temperatures, using a ceramic 119SnO2m source at room temperature with a parabolic motion spectrometer. The linear relationship between isomer shift and ligand electronegativity suggested by Goldanskii for compounds of the type SnX4 has been extended to organo-tin compounds with mixed ligands. On the basis of the observed isomer-shift range, the percentage of ionic character in organo-tin compounds is estimated as lying within an interval of ±5% of a mean value of ∼15%. Binuclear tin compounds of the type R3Sn—SnR3 show no resolvable quadrupole splitting. In aryl-tin compounds, para and meta substitution has little or no effect on the s character of the carbon—tin bond. The ratio ρ of the quadrupole splitting to the isomer shift (with respect to SnO2) has a value larger than 2.10 for compounds in which the Sn atom is sp3d hybridized or in which there is significant departure from tetrahedral symmetry, while ρ values in the range 0 to 1.8 are associated with tetrahedral (sp3 hybridized) tin atoms.