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

Abstract

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)Å, and β= 104.90(5)°, with Z= 4. Refinement on 3 223 non-zero data measured with Cu-K_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)° with Z= 4. Refinement on 5 395 non-zero data measured with Cu-K_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 D_3h symmetry by the bending of SC₆H₄S ligand planes from the relevant TcS₂ planes by 4.1, 1.7, and 1.1°. Factors affecting octahedral versus trigonal-prismatic geometries in these two tris-bidentate complexes are discussed.