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

Abstract

In this work, we have reviewed non-covalent interactions in technetium hexahalide compounds and obtained eight new compounds of the Cat_nTcHal₆ type, where Cat = dimethylammonium, tetramethylammonium, caffeinium, benzothiazolium, nicotinamidium, and pyrazolium, and Hal = Cl, Br. SCXRD studies were carried out for new compounds. In some compounds, halide anions and/or crystallization water were present. In the compounds obtained, an essential influence on the formation of structures and crystal packing is exerted by the molecules of crystallization water and halide ions. Diethylammonium and nicotinamidium compounds, whose structures do not contain other ions and contain sufficiently strong non-covalent interactions, best bind hexahalotechnetates. π-Stacking interactions, anion–π interactions, and halogen bonds were found in the structures. The percentage contribution of the H⋯Hal/Hal⋯H interactions in the transition from fluorine to bromine in TcHal₆²⁻ anions decreases, while the contribution of interactions of other types increases. The greatest variety of interactions in anions is observed for compounds of caffeinium and nicotinamidium with TcBr₆²⁻. The paper considers the processes of thermolysis of some new and previously known Cat_nTcHal₆ compounds with various cations. It is shown that the thermal stability of the compounds is only due to the properties of the organic cation and does not depend on the nature of the halogen. The proposed stages of the process of thermolysis of the TcHal₆²⁻ anion, accompanied by the reduction of technetium to metal, have been established.