Synthesis and crystal structure of Rb6Ta4S22: The first tantalum polysulfide composed of the dimeric complex anion [Ta4S22](6-)

The reaction of Rb2S3, Ta and S in a 1.3:1:5.6 molar ratio at 400 inverted perpendicular C yields red-orange crystals of the new ternary compound Rb6T a4S22 being the first tantalum polysulfide containing the dimeric complex a nion [Ta4S22](6-). The poly sulfide anions are composed of two Ta2S11 subun its which are linked to Ta4S22 units via terminal sulfur ligands. The Ta5centers are coordinated by S-2(2-) and S2- ligands according to [(Ta-2(mu(2 )-eta(2), eta(1)-S-2)(3)(eta(2)-S-2)(S)(2))(2)(mu(2)-eta(1), eta(1)-S-2)](6 -). Every Ta ion is surrounded by seven sulfur ions forming a strongly dist orted pentagonal bipyramid. In the crystal structure the discrete [Ta4S22]( 6-) anions are stacked parallel to the crystallographic b-axis. The Rb+ cations are located between these stacks. Rb6Ta4S22 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.8253(9) Angstrom, b = 7.9665(4) Angstrom, c = 19.174(2) Angstrom, beta=103.215(9)degrees, V = 1751.0(2) Angstrom(3), Z = 2.