Lone pair effects in trihalo-stannate and -plumbate anions in the crystal structures of Sr(MX3)(2) center dot 5H(2)O(M = Sn, X = Cl, Br; M = Pb, X = Br): A joint crystallographic and electronic structure calculation approach

摘要

The crystal structures of Sr(SnCl3)(2) center dot 5H(2)O, Sr(SnBr3)(2) center dot 5H(2)O and Sr(PbBr3)(2) center dot 5H(2)O are presented along with the predicted structure of Sr(PbCl3)(2) center dot 5H(2)O. The compounds are essentially isostructural with Sn/Pb in a trigonal pyramidal environment with Cl/Br. Stereochemical activity of the non-bonding valence electrons on Sn/Pb is evident in the crystal structures, with the degree of distortion less pronounced in the two lead containing structures. Valence electron pair distributions have been examined using a combination of density functional theory and localised Wannier functions. The valence electron distribution around M in the [MX3](-) anion (M = Sn, Pb, X = Cl, Br) is compared in the gas phase and solid state. Electronic structure calculations reveal a contraction towards the metal centre of the orbital associated with the non-bonding valence electrons, on substitution of Sn by Pb. Relatively large deviations of the calculated charge centre maxima from the bond centre in the M-X bonds are an indication of the polarity of the M-X bonds and lead to the conclusion that while the [SnX3](-) anion appears to be a discrete entity within the system Sr(SnX3)(2) center dot 5H(2)O, there is less evidence for the existence of a corresponding discrete [PbX3](-) anion in lead analogues. (c) 2005 Elsevier Ltd. All rights reserved.