PREPARATION, CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES OF TECHNETIUM(II) COMPLEXES WITH 1,2-BIS(DIETHYLPHOSPHINO)ETHANE (DEPE) AND DITHIOCARBAMATE LIGANDS - SINGLE-CRYSTAL STRUCTURAL-ANALYSIS OF [TC((CH3)2NCS2)(DEPE)2](PF6)

Three technetium(II) complexes of the type [Tc(dtc)(DEPE)2]+ have been newly prepared and isolated, where DEPE denotes 1,2-bis(diethylphosph ino)ethane and dtc represents dimethyldithiocarbamate (dmdc), diethyld ithiocarbamate (dedc) or pentamethylenedithiocarbamate (pmdc). The com plexes have been characterized by elemental analysis, UV-vis spectrosc opy, FAB mass spectroscopy, electrochemistry and high performance liqu id chromatography. Bidentate coordination of the dithiocarbamate ligan d is confirmed by a single-crystal structural analysis of the prototyp ical complex [Tc(dmdc) (DEPE)2](PF6). Bond lengths around the approxim ately octahedral technetium(II) centre are Tc-S = 2.449(6), Tc-P (tran s to P) = 2.43(2) and Tc-P (trans to S) = 2.38(2) angstrom. The Tc-P l ength trans to the sulphur atom is significantly shorter than that whi ch is trans to a phosphorus atom. Electrochemical measurements for the [Tc(dtc)(DEPE)2]+ complexes show a reversible technetium(II/I) couple between -0.517 and -0.544 V (vs Ag/AgCl) and another reversible techn etium(III/II) couple ranging from +0.298 to +0.312 V (vs Ag/AgCl) in 0 .5 M TEAP/DMF. The relevance of this chemistry to the design and devel opment of new technetium radiopharmaceuticals is briefly discussed.