SYNTHESIS OF THE QUATERNARY ONE-DIMENSIONAL TRIPLE-CHAIN MATERIALS K3CU3M2Q8 (M = NB, TA - Q = S, SE) - THE STRUCTURE OF K3CU3NB2S8

The one-dimensional triple-chain materials K3Cu3Nb2S8, K3Cu3Nb2Se8, K3Cu3Ta2Se8, and K3Cu3Ta2S8 have been prepared by the reactive flux method in which Cu and Nb or Ta were reacted with K2Q5/Q (Q=S, Se) at 850°C. K3Cu3Nb2S8 has been characterized by single-crystal X-ray diffraction techniques. It crystallizes with four formula units in space group C2h6-C2/c of the monoclinic system in a cell of dimensions a=23.446(3), b=5.545(3), c=14.204(3) Å, β=120.87(3)° at -120°C. It is composed of one-dimensional ∞1[Cu3Nb2S83- chains isolated from one another by K- cations. These chains are triple in nature, and consist of successive corner-sharing CuS4-CuS4 tetrahedra and edge-sharing CuS4-NbS4 tetrahedra. This edge-sharing results in Nb-Cu distances of 2.772(2)-2.781(1) Å. K3Cu3 Nb2Se8 with cell dimensions a=23.453(4), b=5.592(12), c=14.223(3) Å, β=120.7(3)° at -120°C (λ(CuKα1)=1.54056 Å); K3Cu3Ta2Se8 with cell dimensions a=23.493(9), b=5.538(7), c=14.204(12) Å, β=120.5(9)° at -165°C (λ(MoKα1)=0.70930 Å); and K3Cu3Ta2S8 with cell dimensions a=23.450(6), b=5.541(3), c=14.110(6) Å, β=120.47(3)° at -165°C (λ(MoKα1)=0.70930 Å) appear to be isostructural with K3Cu3Nb2S8. K3Cu3Nb2S8 has a resistivity greater than 105 mΩ cm at room temperature. © 1992 Academic Press, Inc.