Novel Synthesis Methods of New Imidazole-derivatives of Tc(IV, V and VII)

What is it about?

In this work, we proposed two new methods for the preparation of [TcO2L4]+ complexes (where L = imidazole (Im), methylimidazole (MeIm)). The reduction of Tc(VII) in an acidic alcoholic solution with thiourea leads to the selective formation of Tc(V). In the absence of a reducing agent, a complex salt Tc(VII) is formed. The reduction of Tc(VII) in an acidic aqueous solution by Sn(II) leads to the formation of a mixture of Tc(V) and Tc(IV) complexes. In a large excess of the reducing agent, the Tc(IV) hexahalides are formed and the formation of double, mixed salt (HMeIm)4[Tc/SnCl6]Cl2 is possible. The main by-products of the reactions are determined and the possible reaction mechanisms are considered. We have shown that the Tc(VII) reduction by thiourea occurs via Tc(III) intermediates, followed by oxidation to Tc(V). The definition of the [TcO2Im4]Br·2H2O crystal structure in the non-centrosymmetric space group suggests that the literature description of the [TcO2Im4]Cl·2H2O structure in the C2/c space group with disordered Cl and water positions may be erroneous. The lengths of the Tc-N and Tc=O bonds in complexes of the [TcO2L4]+ type were refined. A comparative analysis of the non-valent interactions in the obtained crystals showed that with an increase in the size of the anion or the change of Im for MeIm, the intermolecular interactions become weaker. In all of the compounds obtained, except for [TcO2(MeIm)4]TcO4, there are π–stacking interactions between the aromatic rings. The halogen bonds and anion–π interactions were also found in the hexahalide-containing compounds. An analysis of the Hirshfeld surface showed that the main contribution to the crystal packing is made by van der Waals interactions of the type H···H (42.5–55.1%), H···C/C···H (17.7–21.3%) and hydrogen bonds, which contribute 15.7–25.3% in total.

Featured Image

Why is it important?

This type of technetium compounds has multiple applications incluting radiopharmaceutcals, active components of sensors for Tc, molten salts technologies etc.

Perspectives