Coordination compounds with XeF2, AsF3 and HF as ligands to metal ions: a review of reaction systematics, Raman spectra and metal, fluoro-ligand polyhedra

The reactions between Ln(AsF₆)₃ (Ln: lanthanide) and excess of XeF₂ in anhydrous HF (aHF) as a solvent yield coordination compounds Ln(XeF₂)₃](AsF₆)₃ or LnF₃ together with Xe₂F₃AsF₆ or mixtures of all mentioned products depending on the fluorobasicity of XeF₂ and LnF₃ along the series. XeF₂ in a basic aHF is able to oxidize Pr³⁺ to Pr⁴⁺ besides Ce³⁺ to Ce⁴⁺ and Tb³⁺ to Tb⁴⁺. The tetrafluorides obtained are weaker fluorobases as XeF₂ and are immediately exchanged with XeF₂ yielding Xe₂F₃AsF₆ and LnF₄. The analogous reaction between Ln(BiF₆)₃ and XeF₂ in aHF yields Ln(XeF₂)₃](BiF₆)₃, Ln: La, Nd. Raman spectra of the compounds Ln(XeF₂)_n](AF₆)₃ (A: As, Bi) show that no XeF⁺ salts are formed. The interaction of XeF₂ with metal ion is covalent over the fluorine bridge. Analogous reactions of Ln(AsF₆)₃ with AsF₃ in aHF yield Ln(AsF₃)₃](AsF₆)₃ which are stable in a dynamic vacuum at temperatures lower than 233 K. In reactions between M(AF₆)₂ (M: alkaline earth metal and Pb, A: As, Sb) and XeF₂ in aHF as a solvent, compounds of the type M(XeF₂)_n](AF₆)₂ were synthesized. Analogous reactions with AsF₃ yield coordination compounds of the type M(AsF₃)_n](AsF₆)₂. During the preparation of M^x(AsF₆)_x (M: metal in oxidation state x+) by the reaction between metal fluoride and excess of AsF₅ in aHF it was found that HF could also act as a ligand to the metal ions (e.g. Ca(HF)(AsF₆)₂).