Reactions of ThX${}_4$ (X=F, Cl, Br, I) with liquid ammonia-crystal structures and a theoretical study of ammine thorium(IV) halide ammoniates

Reactions of thorium tetrahalides ThX${}_4$ (X=Cl, Br, I) with liquid ammonia at room temperature lead to the formation of decaammine thorium(IV) halide ammoniates. Their different compositions [Th(NH${}_3$)${}_{10}$]X${}_4$ ⋅ nNH${}_3$ were established by single crystal X-ray diffraction. While for the chloride the formation of a tetraammoniate is observed, the reaction of the bromide leads to an octaammoniate, whereas the iodide results in approximately a nonaammoniate. Additionally, the formation of the dinuclear Th complex compound [Th${}_2$Cl${}_2$(NH${}_3$)${}_{14}$(µ-O)]Cl${}_4$ ⋅ 3NH${}_3$ was observed when moisture was present within NH${}_3$. As expected, the Th and the previously reported U compounds [An(NH${}_3$)${}_{10}$]Br${}_4$ ⋅ 8NH${}_3$ (Pbca, An=Th, U), [An(NH${}_3$)${}_{10}$]I${}_4$ ⋅ 9NH${}_3$ (P4/n), and [ An${}_2$Cl${}_2$(NH${}_3$)${}_{14}$(µ-O)]Cl${}_4$ ⋅ 3NH${}_3$ (P$\overline{1}$) are isotypic, respectively. Surprisingly, ThCl${}_4$ formed the decaammine complex [Th(NH${}_3$)${}_{10}$]Cl${}_4$ ⋅ 4NH${}_3$ (P12${}_1$/n1), while UCl${}_4$ formed the octaammine chlorido complex [UCl (NH${}_3$)${}_8$]Cl${}_3$ ⋅ 3NH${}_3$ (Pnma) in ammonia. Quantum-chemical gas-phase calculations were carried out to study the molecular structures and the energetics of the complex cations. In addition, the localized molecular orbitals (LMO) and Intrinsic Bonding Orbitals (IBO) were analyzed. However, the calculations could not explain the preferred formation of the [Th(NH${}_3$)${}_{10}$]${}^{4+}$ complex over the hypothetical cation [ThCl(NH${}_3$)${}_8$]${}^{3+}$. (© 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH)