Coordination of XeF₂ to Calcium and Cadmium Hexafluorophosphates(V)

[M(XeF₂)₅](PF₆)₂ (M = Ca, Cd) complexes were prepared by the reaction of MF₂ and XeF₂ under pressure of gaseous PF₅ in anhydrous HF as solvent. The coordination sphere of the Ca atom consists of nine fluorine atoms:  three from two PF₆^- units (one bidentate and one monodentate) and one from each of six XeF₂ molecules. The coordination sphere of the Cd atom consists of eight fluorine atoms:  one from each of two PF₆^- units and one from each of six XeF₂ molecules. Two of the XeF₂ ligands about M in each compound are bridging ligands and are each linked to two M, generating infinite (−M−F−Xe−F-M−F−Xe−F−) chains along the b-axis in the Ca salt and along the c-axis in the Cd compound. The Cd²⁺ cation is smaller and more electronegative than the Ca²⁺ cation. These differences account for the higher F ligand coordination in the Ca²⁺ salt and for other structural features that distinguish them. The different stoichiometry of the PF₆^- salts when compared with their AsF₆^- analogues, which have the composition [M(XeF₂)₄](AsF₆)₂ (M = Ca, Cd), is in accord with the lower F ligand charge in the AsF₆^- when compared with that in the PF₆^- compound. Indeed, the AsF₆^- ligand charges appear to be similar to those in the XeF₂-bridged species.