Ca(AsF3)(AsF6)2: the first alkaline earth metal cation coordinated to AsF3

Ca(AsF3)(AsF6)2 was prepared by the reaction of CaF2 with excess AsF5 in AsF3 solvent. The compound crystallizes in an orthorhombic crystal system, space group Pnma, with a =1034.9(4) pm, b = 1001.7(4) pm and c = 1088.4(4) pm, V = 1.1283(8) nm3 and Z = 4. Calcium is coordinated to eight fluorine atoms, with six fluorine atoms located at the corners of a regular trigonal prism originating from six AsF6 units. Two rectangular faces of the trigonal prism are capped by fluorine atoms from two fluorine bridged AsF3 molecules. For the first time, AsF3 is shown to serve as a bridging ligand to two metal cations, with bridging distances of F(AsF3)–Ca = 241.1 and 243.2 pm. It was found, again for the first time, that the bridging As–F distances are shorter (172.4 and 173.1 pm) than the terminal As–F distance (184.5 pm). The Raman spectrum shows vibrational modes that are readily assigned to AsF3 and AsF6−.