CRYSTAL AND ELECTRONIC-STRUCTURE OF THE TETRAHEDRAL V-4 CLUSTER COMPOUNDS GEV(4)Q(8) (Q = S, SE)

New tetrahedral metal cluster compounds were synthesized and character ized by means of single crystal Xray methods. GeV4S8 (F (4) over bar 3 m, Z = 4, a = 9.655(1) Angstrom) and GeV4S8 (n = 10.139(1) Angstrom) c rystallize in the GaMo4S8-structure, built up by cubane-like (V4S4)(4) and tetrahedral (GeS4)(4-) units arranged in the NaCl manner. The el ectronic structure is investigated by the LMTO method. Electron densit y and Electron localization function (ELF) maps show details of the ch emical bonding, revealing the earlier used description of these materi als as spinels to be inappropriate. Metal-metal bonding within the tet rahedral V-4 clusters is analyzed by using real space techniques. GeV4 S8 is semiconducting and exhibits antiferromagnetism at T-N = 13 K. An anomaly in the susceptibility is observed at 196 K. The properties of GeV4S8 are discussed within the framework of spin-polarized band calc ulations. GeV4S8 turns out to be a Mott-Hubbard insulator.