Preparation and crystal structures of bis(tetraphenylarsonium) tris(oxalato)technetate(IV), and tetraphenylarsonium tris(benzene-1,2-dithiolato)technetate(V): octahedral versus trigonal-prismatic geometry for tris-bidentate complexes of technetium

The addition of [NH4]2[TcBr6] to an aqueous solution of oxalic acid yields the complex [AsPh4]2[Tc(ox)3] (1), and the reaction of benzene-1,2-dithiol (H2bdt) with [AsPh4] [TcNCl4] in acetone yields crystals of [AsPh4] [Tc(bdt)3] (2). The syntheses and crystal structures of the two compounds are reported. [AsPh4]2[Tc(ox)3] crystallises in the monoclinic space group C2/c with cell parameters a = 23.164(2), b = 13.507(2), c = 16.047(1) A, and β 104.90(5)0, with Z = 4. Refinement on 3 223 non-zero data measured with Cu-Ksub(α) radiation converged to R 0.054. The co-ordination geometry of the technetium (IV) atom and the six co-ordinated oxygen atoms is distorted octahedral and of pseudo-D3 symmetry. Crystals of (2) are monoclinic, space group P21/n with a = 12.966(1), b = 12.746(1), c = 23.233(1), and β = 92.27(8)0 with Z = 4. Refinement on 5 395 non-zero data measured with Cu-Ksub(α) radiation converged to R 0.048. The technetium(V) atom is co-ordinated to six sulphur atoms in close to ideal trigonal-prismatic geometry. The complex is distorted from ideal Dsub(3h) symmetry by the bending of SC6H4S ligand planes from the relevant TcS2 planes by 4.1, 1.7, and 1.10. Factors affecting octahedral versus trigonal-prismatic geometries in these two tris-bidentate complexes are discussed. (author)