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 S^2– ions to S₂^2–. 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)Å, β= 97.3(1)°, and Z= 4; (2), triclinic, space group P, a= 11.826(11), b= 12.021(11), c= 10.813(13)Å, 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)Å, 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)Å 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.