ELECTRONIC-STRUCTURES AND GEOMETRIES OF 6-CO-ORDINATE BIS(TROPOLONATE)TIN HYDROCARBYL AND CHLORIDE COMPLEXES - A COMBINED THEORETICAL AB-INITIO AND GAS-PHASE PHOTOELECTRON-SPECTROSCOPY STUDY

The intriguing relationship between the electronic properties and geom etrical structure of six-co-ordinate tin(rv) complexes of general form ula SnL(2)(trop)(2) (L = CI, CH3, C2H5 or C6H5; Htrop = tropolone) has been studied by theoretical ab initio calculations and experimental g as-phase UV photoelectron spectroscopy. In agreement with X-ray diffra ction data, the theoretical results indicate more stable cis arrangeme nts for both SnCl2(trop)(2) and Sn(CH3)(2)(trop)(2). The trans conform ations represent local minima with higher energy (10 and 13 kcal mol(- 1), respectively). The gas-phase UV photoelectron spectra were assigne d using ab initio data as well as photoelectron data for closely relat ed complexes. The energy and the relative stabilities of molecular orb itals associated with sigma(Sn-L) bonds are modulated by the L-Sn-L bo nd angle and, therefore, the corresponding photoelectron ionization da ta can be diagnostic of the molecular shape. The almost ubiquitous cis geometries of bis-chelate tin(rv) dihalide complexes can be contraste d with the greater flexibility of dimethyl complexes which adopt eithe r cis or trans structures depending upon the nature of the chelating l igands. This observation can be rationalized in terms of a different i nvolvement of metal orbitals in the metal-ligand bonding.