SYNTHESIS AND CHARACTERIZATION OF NEUTRAL TECHNETIUM(III) COMPLEXES WITH MIXED S,P-BIDENTATE PHOSPHINE THIOLATE LIGANDS - CRYSTAL-STRUCTURE OF [TC(SCH2CH2PPH2)2(SCH2CH2PPH2O)]

Reduction-substitution reactions of [TcO4]- with an excess of the mixed bidentate thiol-phosphine ligands HL(n) [L1 = 2-(diphenylphosphino)ethanethiolate; L2 = 2-(diphenylphosphino)propanethiolate and L3 = 2-(diphenylphosphino)thiophenolate] gave neutral five-co-ordinate technetium(III) complexes of the type [TcL(n)2(O=L(n))] (n = 11 or 22). However, the aromatic phosphine-thiol ligand (n = 3) gave six-co-ordinated [TcL3(3)]3. The five-co-ordinated complexes are diamagnetic and exhibit a trigonal-bipyramidal geometry in which two pi-acid phosphorus donors of two chelates are co-ordinated mutually trans in the axial positions, with the corresponding thiolate sulfur atoms on the equatorial plane. A further thiolate group completes the basal-plane co-ordination leaving a pendant phosphorus donor outside the co-ordination sphere. This is oxidized to phosphine oxide, which was revealed by a crystal structure determination of 1: triclinic, space group P1BAR, with Z = 2, a = 9.991 (4), b = 12.417(4), c = 18.687(8) angstrom, alpha = 73.37(3), beta = 76.88(3) and gamma = 73.68(3)-degrees; R converged to 0.0703 using 2765 observed reflections. In addition, the compounds were characterized by elemental analysis, IR, H-1 and P-31 NMR, UV/VIS and FAB spectroscopies and cyclic voltammetric measurements. The occurrence of trigonal-bipyramidal vs. octahedral geometry is discussed in terms of ligand steric requirements and electronic factors governing the metal-donor interactions.