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 Mx(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).