Mössbauer studies of matrix-isolated SnO, Sn2O2 and higher polymers

Abstract

Mössbauer and infra-red spectra of a series of molecular tin(II) oxides, isolated in solid nitrogen at 5 K, have been measured. Mössbauer isomer shifts of 3.03 and 2.88 mm s^–1 relative to BaSnO₃ are obtained for SnO and Sn₂O₂. The respective quadrupole splittings are 4.53 and 3.73 mm s^–1. A broader doublet representing higher polymers, of which Sn₄O₄ was the only one evident in the i.r., has an isomer shift of 2.8 mm s^–1 and a smaller quadrupole splitting of 2.3 mm s^–1. The simple species have similar Mössbauer recoil-free fractions, and a value of approximately f= 0.4 at 4.2 K is deduced. The dependence of f on temperature up to 14.9 K can not be described by the mass-defect model, and indicates the presence of enhanced force constants between the SnO molecules and nitrogen. SCF MO calculations for SnO show that the Sn 5s population is only slightly less than 2, and predict a point on the isomer shift against electron density scale in support of that previously obtained from Sn atoms.