High-co-ordination-number compounds of niobium and tantalum: reactions of niobium and tantalum halides and sulphide-halides with sodium diethyldithiocarbamate. The crystal structures of [Nb(S2CNEt2)4]Br, Nb(S2CNEt2)3S, and Ta(S2CNEt2)3(S2)

Abstract

The reactions of Na(S₂CNEt₂) with niobium(V) halides lead to the formation of a mixture from which [Nb(S₂CNEt₂)₄]Br, (1), and Nb(S₂CNEt₂)₃S, (2), can be separated. The corresponding reactions with tantalum sulphide-halides gave Ta(S₂CNEt₂)₃S and Ta(S₂CNEt₂)₃(S₂), (3). The products (1)–(3) have been characterised by single-crystal X-ray structure determinations: (1), monoclinic, space group P2₁/a, a= 11.100(8), b= 27.910(18), c= 10.680(9)Å, β= 92.8(1)°, and Z= 4; (2), triclinic, space group P, a= 16.892(14), b= 9.868(8), c= 15.747(14)Å, α= 91.0(1), β= 78.1(1), γ= 85.8(1)°, and Z= 4; (3), monoclinic, space group C2/c, a= 16.319(9), b= 10.887(8), c= 30.322(25)Å, β= 88.0(1)°, and Z= 8. For compound (1), 2 612 above background data were collected on a diffractometer and the structure refined to R 0.081; for (2) and (3) the corresponding values are 5 058, R= 0.054 and 1 814, R= 0.099 respectively. The structure of (1) is ionic and contains the [Nb(S₂CNEt₂)₄]⁺ cation in which the metal is eight-co-ordinate with mmmm dodecahedral symmetry. The Nb–S distances range from 2.511(5) to 2.593(4)Å. The structure of (2) comprises two crystallographically distinct seven-co-ordinate monomers of Nb(S₂CNEt₂)₃S of similar geometry, both with a multiple NbS bond [2.164(3) and 2.112(3)Å] and three chelating S₂CNEt₂ ligands. In both molecules the metal geometry is pentagonal bipyramidal with the multiple bond in an axial position. The structure of (3) contains discrete molecules of Ta(S₂CNEt₂)₃(S₂) which are eight-co-ordinate with the metal in a distorted dodecahedral environment. Four m edges are occupied by three S₂CNEt₂ ligands and a side-on bonded disulphide group. The Ta–S distances range from 2.375(12) to 2.598(10)Å with a S–S distance of 2.074(17)Å.