Crystal structures and preparation of K2AgVS4 and Rb2AgVS4 by using the molten flux method: Low-dimensional materials with infinite metal-ion-centered tetrahedra chains

The quaternary sulfides K2AgVS4 and Rb2AgVS4 crystallize as dark violet needle-like crystals with a metallic lustre. Infinite Ag- and V-centered tetrahedra sharing common edges are running parallel to the crystallographic a axis. The chains are separated by K+ or Rb+ ions which are in an eightfold environment. The tetrahedra are occupied in an ordered fashion. The Ag-V interatomic distances amount to 2.904(1) and 2.910(1) Angstrom, respectively, which is significantly larger than the sum of the ionic radii of Ag+ and V5+. Whereas the V-S distances are in the normal range, the average (Ag-S) distances are the shortest reported so far indicating strong covalent bonding between monovalent Ag+ and S2-. In addition, the title compounds represent very rare examples of AgS4 polyhedra with equidistant Ag-S bonds. The geometrical parameters within the tetrahedra chains are only slightly affected when K+ is replaced by the larger Rb+ demonstrating the rigidity of the bonding properties within the tetrahedra. The compounds are isotypic with the quaternary copper sulfide K2CuVS4 and the selenides K(2)CuMSe(4)(M=Nb, Ta).