Lone pair effects in trihalo-stannate and -plumbate anions in the crystal structures of Sr(MX3)2 · 5H2O (M = Sn, X = Cl, Br; M = Pb, X = Br): A joint crystallographic and electronic structure calculation approach

The crystal structures of Sr(SnCl3)2 · 5H2O, Sr(SnBr3)2 · 5H2O and Sr(PbBr3)2 · 5H2O are presented along with the predicted structure of Sr(PbCl3)2 · 5H2O. 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 · 5H2O, there is less evidence for the existence of a corresponding discrete [PbX3]− anion in lead analogues.

Electronic structure calculations in combination with X-ray crystallography have been used to examine valence electron pair distribution in Sr(MX3)2 · 5H2O (M = Sn, X = Cl, Br; M = Pb, X = Br) and total energy minimisation methods used to predict the structure of Sr(PbCl3)2 · 5H2O.Figure optionsDownload as PowerPoint slide