Synthesis, spectroscopy, and structural characterization of neutral seven-coordinate technetium xanthate complexes. X-ray structure of [Tc(PPh3)(S2COC4H9)3], a capped octahedral technetium(III) complex

Abstract

Reaction of (Bu 4 N)[TcOCl 4 ] with triphenylphosphine and an excess of potassium xanthate yields neutral complexes of the general formula [Tc(PPh 3 )(S 2 COR) 3 ] (R=ethyl, isopropyl, n-butyl, neopentyl). The infrared spectra show a single C=S absorption from the exclusively bidentate xanthate ligands. The fast-atom-bombardment mass spectral results show the parent ions and a complex fragmentation pattern that includes two sulfido species. The X-ray structure of [Tc(PPh 3 )CS 2 COBu n ) 3 ] confirms the unusual seven-coordinate, capped octahedral geometry, with the technetium and phosphorus atoms each sitting on 3-fold axes and a single crystallographically unique n-butyl xanthate ligand. Crystal data for C 33 H 42 O 3 PS 6 Tc: rhombohedral space group (hexagonal axes) R3c(h), a=15.437 (4) A, c=53.49 (1) A, V=11040 A 3 to give Z=12 for D=1,46 g/cm 3 ; structure solution and refinement based on 1726 reflections converged at R=0.043, R w =0.047. The 1 H NMR spectra show that the 3-fold molecular symmetry is maintained in solution, with a single set of C-H absorptions from the three xanthate ligands. The 99 Tc NMR resonances of these complexes fall in the Tc(V) region and are the first technetium complexes with sulfur ligation to be so characterized