Ammonium 18-crown-6 complexes with tetrahedral monoanions: X-ray, thermal and comparative analysis of non-covalent interactions

Abstract

We report the preparation, crystal structures, and non-covalent interaction analysis for a series of ammonium–18-crown-6 complex salts with tetrahedral monoanions, [(NH₄)(18C6)]⁺[TX₄]⁻·nH₂O, TX₄⁻ = BF₄⁻ (n = 0), TcO₄⁻ (n = 1), ReO₄⁻, OsO₃N⁻, CrO₃F⁻, CrO₃Cl⁻, and CrO₃Br⁻. In accordance with the size of the anion, the structures can be divided into several groups: “pseudo-dimeric anhydrous” {[NH₄(18C6)]₂(TX₄)}⁺[TX₄]⁻ for the tetrafluoroborate, monofluorochromate, and the previously reported perchlorate; “monomeric hydrate” for pertechnetate and nitridoosmate, and “monomeric anhydrous” for the perrhenate and the remaining monohalochromates. Thermal analysis was performed for compounds with different anion natures. The dependence of the complexes' thermal destruction temperature on the anion's oxidizing ability was shown. IR and MALDI analyses were performed for some complexes. The influence of crown ether on the processes of solubility and extraction of the pertechnetate anion in systems with organic solvents is shown.