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

Abstract

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.

Influence of the organic cation on the formation of hexahalotechnetates: X-ray, thermal and comparative analyses of non-covalent interactions

“…For compounds with thiourea (DTu 2 (TcBr 6 )Br 2 ·3H 2 O ( 9 ), DTu 2 (TcCl 6 )Cl 2 ·3H 2 O ( 10 )) and imidazolium (HIm 2 TcBr 6 ( 11 ), HIm 2 TcCl 6 ( 12 )), good quality structures have been described in our previous works. 6,41 Structures 2 , 6–8 contain only organic cations and hexahalide anions; the rest additionally contain water molecules or halide anions (Fig. 1).…”

“…2.4 Synthesis of HIm 2 TcBr 6 (11) and HIm 2 TcCl 6 (12) We obtained compounds 11 and 12 according to the procedure described in previous articles. 6,41 Reaction yields of Tc: 11 -70%; 12 -75%.…”

“…In the work, we obtained eight new crystal structures of hexahalotechnetates with organic cations of different structures: caffeinium ((HCaf ) (12)), good quality structures have been described in our previous works. 6,41 Structures 2, 6-8 contain only organic cations and hexahalide anions; the rest additionally contain water molecules or halide anions (Fig. 1).…”

“…We obtained compounds 11 and 12 according to the procedure described in previous articles. 6,41 Reaction yields of Tc: 11 – 70%; 12 – 75%.…”

“…The formation of technetium-halogen bonds has been reliably documented for a series of technetium coordination compounds exhibiting the oxidation states Tc(VII), 1 Тс(VI), 2 Tc(V), 3 Tc(IV), 4,5 Tc(III), [6][7][8] Tc(II), [9][10][11] and Tc(I), and also in the form of clusters with fractional oxidation states. 12,13 Under specific conditions, technetium also forms carbonyl-halide compounds that could be precursors for various radiopharmaceuticals.…”