Thiourea as a Stabilizer of Reduced Forms of Technetium─Tc(III) and Tc(IV): Experimental and Theoretical Studies of Complexes.

This paper presents synthetic methods for the preparation of Tc(III) and Tc(IV) coordination compounds with thiourea. We have shown that the main product of the synthesis is the complex [TcTu 5 X]X 2 , (Tu = (NH 2 ) 2 CS, X = Cl, Br) and not [TcTu 6 ]Cl 3 ·4H 2 O, as previously thought. Tu 2 [TcX 6 ]X 2 ·3H 2 O is the main technetium-containing byproduct of the reaction. All reaction products, including byproducts, were characterized by X-ray diffraction analysis. We also measured the solubility for the obtained Tc(III) complexes. This research work considers the process of thermolysis of the obtained Tc(III) complexes and shows that the presence of sulfur atoms in the coordination sphere can inhibit the process of metal formation in an argon-hydrogen medium. The analysis of nonvalent interactions in Tc(III) complexes showed that the main contribution is made by van der Waals interactions of the H···H type (40.8-42.3%) and hydrogen bonds Hal···H/H···Hal and H···S/S···H, which are 41.6-44.5% in total. As the temperature decreases, the proportion of H···H contacts and H bonds decreases, and when the halogen (Cl by Br) is replaced, the proportion of H bonds increases and the proportion of van der Waals interactions decreases.