Crystal structure and lattice energy of thallium(I) fluoride: inert-pair distortions

Abstract

The crystal structure of TlF has been redetermined from X-ray single-crystal (R 0·101; 105 observed reflections) and neutron powder data. Crystals are orthorhombic with a= 5·1848(2), b= 6·0980(3), c= 5·4916(2)Å, Z= 4, space group Pm2a. Two independent thallium ions have similar environments, surrounded by octahedra of fluoride ions, with two close approaches (Tl ⋯ F 2·25–2·62 Å), two intermediate distances, and two (cis) long approaches (Tl ⋯ F 3·07–3·90 Å). The lattice energy is recalculated as –781·9 kJ mol^–1, but it is concluded that the presence of an aspherical thallium ion probably means that the model used for the calculation is inadequate.