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.