Electrostatic Energy in Inorganic and Organic Salts Containing Octahedral SnCl₆^2- Ion

Abstract

Hexachlorostannic acid is a precursor of derivatives of an ionic nature. The electrostatic part of the lattice energy in alkali metal salts and nitrogen organic base salts containing the SnCl₆^2- ion was determined by adopting the Ewald method. This approach requires knowledge of the complete or at least partial crystal structures of the compounds. In the case of incomplete structures the MNDO geometry optimization procedure was successfully applied to find the unknown positions of atoms, and thus permitted a wider representation of compounds to be considered. The crystal lattice energy calculations were carried out by taking from four different literature sources data regarding charge distribution in SnCl₆^2-. It was further assumed that the positive charge in cations was located either directly on certain atoms or distributed between all the atoms in these ions. These latter net atomic charges were evaluated by applying INDO and MNDO methods. The electrostatic energies derived compare well with published values of the crystal lattice energy; this implies that, in the case of the compounds examined, the main contribution to the cohesive forces is made by Coulombic interactions.