A(6)Nb(4)S(22) (A=Rb and Cs), compounds with the tetrameric complex anion [Nb4S22](6-): Preparation via the molten flux method and crystal structure determination

The new ternary niobium polysulfides A(6)Nb(4)S(22) were prepared at a low temperature of 350 degrees C via the molten flux method by reacting A(2)S(3) (A = Rb, Cs) with niobium metal and additional sulfur. The crystal structure is characterized by [Nb4S22](6-) anions. Two Nb2S10 subunits are joined by a S-2(2-). Nb5+ is coordinated by S-2(2-) and S2- ligands according to [Nb-2(mu - eta(2), eta(1) - S-2)(eta(2) - S-2)(3)(S)(2)](2)(mu - eta(1) - S-2)(6-). Every Nb is in a sixfold coordination, and the polyhedra can be regarded as strongly distorted pentagonal pyramids. Within the unit cell the anions are stacked in ''rods'' parallel to the crystallographic b-axis. These stacks are arranged in ''layers'' and the A(+) ions are located between the layers.