Synthesis and characterization of [M(III)(PS)2(L)] mixed-ligand compounds (M = Re, 99Tc; PS = phosphinothiolate; L = dithiocarbamate) as potential models for the development of new agents for SPECT imaging and radiotherapy.

The synthesis and characterization of a new series of neutral, six-coordinated mixed-ligand compounds [M(III)(PS)2(L)] (M = Re; (99)Tc), where PS is bis(arylalkyl)- or trialkylphosphinothiolate and L is dithiocarbamate, are reported. Stable [M(III)(PS)2(L)] complexes were easily synthesized, in good yield, starting from precursors where the metal was in different oxidation states (III, V, and VII), involving ligand-exchange and/or redox-substitution reactions. The compounds were characterized by elemental analysis, positive-ion electrospray ionization mass spectrometry, multinuclear NMR spectroscopy, cyclic voltammetry, and X-ray diffraction analysis. All complexes are constituted by the presence of the M(III)(PS)2 moiety, where two phosphinothiolate ligands are tightly bound to the metal and the remaining two positions are saturated by a dithiocarbamate chelate, also carrying bulky bioactive molecules [e.g., (2-methoxyphenyl)piperazine]. X-ray analyses were performed on crystalline specimens of four different Re/(99)Tc compounds sharing a distorted trigonal-prismatic geometry, with a P2S4 coordination donor set. The possibility of easily preparing these [M(III)(PS)2(L)] complexes, starting from the corresponding permetalate anions, in mild reaction conditions and in high yield, lays the first stone to the preparation of a new series of M(III)-based (M = (99m)Tc/(188)Re) compounds potentially useful in theragnostic applications.