Is Tl2Ni3S2 a mixed valent compound? Crystal and electronic structure investigations

The crystal and electronic structure of Tl2Ni3S2 is investigated by X-ray structure determination and DFT calculations. The question of charges and possible mixed valences of two different Tl positions in Tl2Ni3S2 is discussed with respect to crystal and electronic structure arguments. Crystal structure parameters were redetermined from single crystal data. A relation is given to typical Tl states in reference compounds like mixed valent Tl2S2, high-pressure TlS, LiTl, and ThCr2Si2 type TlNi2S2. This allows for a comparison of different Tl sites with respect to atomic distances, coordinations, valence, charge, and bonding as well as charge redistribution within layered Ni–S substructures. Complementary methods of charge determination from theory are applied as orbital analysis from precise full potential calculations and charge density analysis by zero flux surface integration according to the AIM theory.

Graphical abstractCan charge and valence of Tl be determined by comparison from different coordination spheres and electronic structure calculations? Tl sites in Tl2Ni3S2 are compared to related compounds including mixed valent Tl2S2.Figure optionsDownload full-size imageDownload as PowerPoint slide