Crystal structures of tris(NN-diethyldithiocarbamato)oxo-niobium(V) and -vanadium(V)

The crystal and molecular structures of the isomorphous and isostructural title compounds [MO(CS₂·NEt₂)₃][(I), M = Nb; (II), M = V] have been determined by single crystal X-ray diffraction, the structures being solved by heavy-atom methods and refined by least-squares methods to R 0·096 [(I) 1680 visually estimated reflections] and 0·103 [(II) 671 diffractometer reflections]. Both are monoclinic, space group P2₁/a, Z = 4; (I): a = 17·28(1), b = 13·305(5), c = 10·774(5) Å; β = 90·09(6)°; (II): a = 17·27(1), b = 13·22(1), c = 10·72(1) Å, β = 90·5(1)°. In each structure the seven-co-ordinate metal atom is surrounded by an oxygen atom [Nb=O, 1·74(1), V=O, 1·65(2) Å] and three bidentate dithiochelates, two lying in the equatorial plane of a distorted pentagonal bipyramid. The five equatorial distances are almost equal (Nb-S 2·547-2·596, V-S 2·46-2·50 Å) while that opposite to the oxygen is longer (Nb-S 2·753, V-S 2·63 Å). All 0=M-S angles are greater than 90°.