Preparation and crystal structure of carbonyltris(diethyldithiocarbamato) technetium(III) : an unexpected source of co-ordinated carbon monoxide

Abstract

The title compound [Tc(S2CNEt2)3(CO)] has been prepared by the reduction of [NH,][TcO4] with aminoimino-methanesulphinic acid in the presence of Na[S2CNEt2]. It is suggested that the co-ordinated carbon monoxide is formed after co-ordination of aminoiminomethanesulphinic acid, or some decomposition product, with technetium. The crystal structure of [Tc(S2CNEt2)3(CO)] has been determined by single-crystal X-ray diffraction methods at 17 °C. Crystals are triclinic, space group P, with a= 9.510(1), b= 9.976(1), c= 14.637(3)A, α= 103.79(1), β= 105.42(1), γ= 72.52(1)°, and Z= 2. Diffractometry has provided significant Bragg intensities for 2 045 independent reflections and the structure has been refined by full-matrix least-squares methods to R 0.049. The compound is isostructural with the rhenium analogue and consists of discrete [Tc(S2CNEt2)3(CO)] molecules, each containing a terminal ‘linear’ CO group. The technetium atom has a seven-co-ordinate environment which is best described as a distorted pentagonal bipyramid. The geometry of the TcIII–C–O group [Tc-C 1.861(12), C–O 1.15(1)A], by comparison with the ReIII–C–O case, indicates that technetium is a poorer π-donor than is rhenium.