Molecular spectroscopy of organometallic compounds: Organotin(IV) tropolonates

Abstract

The infrared, Raman, and 119Sn Mössbauer spectra of seven organotin tropolonates (R2SnT2), (C6H5)SnT3, and bis tropolonatotin(IV) dichloride have been examined in detail. The diorganotin(IV) compounds have a six-coordinate structure with the two organic ligands occupying either cis (R=CH3, C6H5, and C6H5CH2) or trans (R=C2H5, n-C3H7, n-C4H9) positions. Owing to the asymmetric nature of the tropolone ligand, none of these structures have a center of symmetry in the solid state and both the symmetric and asymmetric Sn–C stretching vibrations are Raman active. The temperature dependence of the recoil-free fraction for the diorganotin(IV) tropolonates has been determined over the temperature range 78?T<∼140 K and can be correlated with the Raman data in the lattice mode region to yield a self-consistent assignment of the intermolecular, intra-unit-cell vibration in the solids and a value of the effective vibrating molecular mass. From the latter data it is inferred that these complexes are monomeric in the solid state with (relatively) weak intermolecular bonding forces between adjacent molecules. The tropolone ligand can thus be envisioned as acting as an anisobidentate moiety with both oxygen atoms bonded to a single metal center. The temperature dependence at the 119Sn isomer shift with respect to BaSnO3 and of the quadrupole hyperfine interaction for these compounds is also reported.