SQUARE, SULFUR-BICAPPED TETRANIOBIUM CLUSTER COMPOUNDS

By addition of first PhSSPh and then PMe2R (R = Ph, Me) to a solution of NbCl5 that has been reduced with Na/Hg, the orange, crystalline compounds Nb4S2(SPh)8(PMe2Ph)4·C7H8 (1) and Nb4S2(SPh)8(PMe3)4·C7H8·C4H8O (2) are obtained. They are closely related to the [Nb4S2(SPh)12]4- anion previously reported by Christou and co-workers (L. Seela, J. C. Huffman and G. Christou, J. Chem. Soc., Chem. Commun. 1987, 1258). In each compound four niobium and two sulphur atoms form a tetragonal bipyramid with sulphur atoms at the apices. The mean NbNb and NbSap distances are, respectively, 2.816(8) and 2.491(3) Å, for 1 and 2.812(6) and 2.404(3) Å for 2. Each NbNb bond (postulated to be single) is bridged by two SPh groups (mean NbSbbr distances for 1 and 2 are 2.624(8) and 2.626(3) Å, respectively) and there is a phosphine ligand coordinated to each niobium atom (mean NbP distances for 1 and 2 are 2.706(1) and 2.677(4) Å, respectively). Compound 1 crystallizes in triclinic space group P1 with unit cell dimensions: a = 13.411(6), b = 14.588(4), c = 13.058(5) Å, α = 98.05(3), β = 114.95(3), γ = 66.35(3)°, V = 2210(2) Å3 and dcalc = 1.530 for Z = 1. The structure was refined to R = 0.0439 and Rw = 0.0590 for 4740 reflections with I > 3σ(I). Compound 2 crystallizes in monoclinic space group C2/m with unit cell dimensions: a = 19.333(10), b = 19.965(8), c = 12.048(5) Å, β = 120.00(4)°, V = 4027(7) Å3 and dcalc = 1.466 for Z = 2. The structure was refined to R = 0.0547 and Rw = 0.0674 for 1480 reflections having I > 3σ(I). © 1990.