Preparation and crystal structures of [AsPh4]4[Tc4N4O2(ox)6] and [AsPh4]2[TcO(ox)2(Hox)]·3H2O: technetium complexes containing quadridentate or unidentate oxalato ligands

Abstract

The reaction of oxalic acid (H₂ox) with [AsPh₄][TcNCl₄] and [NBu₄][TcOCl₄] in aqueous acetone yields crystals of [AsPh₄]₄[Tc₄N₄O₂(ox)₆](1) and, after precipitation with AsPh₄Cl, [AsPh₄]₂[TcO(ox)₂(Hox)]·3H₂O (2) respectively. Complex (1) crystallises in the monoclinic space group P2₁/n with cell parameters a= 14.433(1), b= 13.229(1), c= 27.020(1)Å, β= 92.90(1)°, and Z= 4. Refinement with data measured with Cu-K_α radiation converged at R= 0.069 for 3 076 observed reflections. The anion in (1) is a cyclic tetranuclear complex, [Tc₄N₄O₂(ox)₆]^4–, with C_i point symmetry. Each technetium(VI) atom is co-ordinated by five oxygen atoms and one nitrogen atom to give a distorted octahedron. In each half of the anion, a quadridentate oxalato ligand forms a bridge between the two octahedra, each of which is also linked to an adjacent octahedron by the corner sharing of an oxo ligand. Two oxygen atoms of a bidentate oxalato ligand and a nitrido nitrogen complete the octahedral co-ordination in each polyhedron. The Tc ⋯ Tc spacings of 3.586(2) and 5.756(3)Å preclude any Tc–Tc bonding. The monoclinic crystals of complex (2) belong to the space group P2₁/c with a= 16.495(3), b= 14.802(2), c= 21.805(4)Å, β= 98.76(1)°, and Z= 4. Refinement with 5 099 observed data measured with Mo-K_α radiation converged at R= 0.059. The technetium(V) atom is co-ordinated by six oxygen atoms to give a distorted octahedron. The structure of the anion is unusual in that it contains a protonated unidentate oxalato ligand and that there is no appreciable lengthening of the Tc–O bond trans to the oxo ligand.