Electronic structures and geometries of six-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 geometrical structure of six-co-ordinate tin(rv) complexes of general formula SnL(2)(trop)(2) (L = CI, CH3, C2H5 or C6H5; Htrop = tropolone) has been studied by theoretical ab initio calculations and experimental gas-phase UV photoelectron spectroscopy. In agreement with X-ray diffraction data, the theoretical results indicate more stable cis arrangements for both SnCl2(trop)(2) and Sn(CH3)(2)(trop)(2). The trans conformations represent local minima with higher energy (10 and 13 kcal mol(-1), respectively). The gas-phase UV photoelectron spectra were assigned using ab initio data as well as photoelectron data for closely related complexes. The energy and the relative stabilities of molecular orbitals associated with sigma(Sn-L) bonds are modulated by the L-Sn-L bond angle and, therefore, the corresponding photoelectron ionization data can be diagnostic of the molecular shape. The almost ubiquitous cis geometries of bis-chelate tin(rv) dihalide complexes can be contrasted with the greater flexibility of dimethyl complexes which adopt either cis or trans structures depending upon the nature of the chelating ligands. This observation can be rationalized in terms of a different involvement of metal orbitals in the metal-ligand bonding.