The reactions of tetrahydrothiophene (tht) with tribromosulphidoniobium(V) and trichlorosulphidoniobium(V) and the crystal structures of three of the products Nb2Cl4S3·4tht, Nb2Br4S3·4tht, and NbBr3S·2tht

Abstract

The niobium(IV) compounds [(tht)2X2Nb(µ-S)(µ-S2)NbX2(tht)2][X = Cl (1) or Br (2)] are formed through a complex redox–disproportionation reaction when NbX3S is treated with tetrahydrothiophene (tht). The reduction occurs via the oxidation of two formal S2– ions to S22–. It is thought that initially NbX3S·2tht (3) is formed in the reaction. The reaction has been characterised by crystal-structure determinations of compounds (1), (2), and (3; X = Br) : (1), monoclinic, space group P21/c, a= 12.483(15), b= 11.818(17), c= 19.798(17)A, β= 97.3(1)°, and Z= 4; (2), triclinic, space group P, a= 11.826(11), b= 12.021(11), c= 10.813(13)A, α= 101.4(1), β= 96.2(2), γ= 98.8(2)°, and Z= 2; (3), monoclinic, space group P21/m, a= 8.018(12), b= 8.802(15), c= 11.887(12)A, β= 103.9(1)°, and Z= 2.1 968 Independent diffractometer data for (1) have been refined to R 0.068, 522 and 571 to 0.061 and 0.064 for (2) and (3) respectively. The structures of compounds (1) and (2) are similar in that they contain two niobium atoms bridged by a sulphur atom and a disulphide group. The Nb–Nb distances of 2.844(2) and 2.830(5)A respectively are indicative of a single metal–metal interaction. The metal co-ordination spheres are completed by two halogen atoms and two sulphur atoms of the tht ligands. In compound (3) the metal atom is six-co-ordinate, being bonded to a terminal sulphur, three bromine atoms, and two tht ligands through sulphur atoms. The multiple NbS bond is trans to a tht ligand. Both compounds (1) and (3) are disordered.