Synthesis and crystal structures of Cs5Nb2S4X9 -: Double salts containing new cluster anions [Nb2(μ-S2)2X8]4- (X = Cl, Br)

Bis(disulfide)bridged Nb(+4) cluster halide complexes [Nb2S4X8](4-) (X = Cl, Br) were prepared by acid hydrolysis of [Nb2S4(NCS)(8)](4-) in concentrated aqueous HCl or HBr, solution from which they can be isolated as double salts Cs-5[Nb2S4X8]X (X = Cl, 1; X = Br, 2). The crystal structures of 1 and 2 were determined. The isolation and Xray structure of oxonium salt (H3O)(5) [Nb2S4Cl8]Cl (3) is also reported. 1-3 contain new [Nb2S4X8](4-) anions which can also be viewed as excised building blocks of polymeric solids NbS2X2. The extra halogen resides in the center of octahedron formed by six Cs+ or H3O+ ions. All the three salts are isostructural and crystallize in tetragonal space group Immm with the following parameters: a = 10.269(2), b = 16.343(2), c = 7.220(1)Angstrom for 1, a = 10.934(1), b = 16.613(2), c = 7.470(1) Angstrom for 2, a = 9.639(1), b = 16.031(1), c = 7.071(1) Angstrom for 3. The parameters of the Nb2S4 core are only slightly affected by the change from Cl to Br.