Palladium Chemistry in Anhydrous HF/AsF5 Superacid Medium

Pd metal dissolves in anhydrous HF (aHF) acidified with AsF5 in the presence of F2 at ≈︁298 K to give a blue‐green solution from which green Pd(AsF6)2 can be isolated. The latter was also prepared by the interaction of PdF2 and AsF5 in aHF or by the reaction between PdO and F2 in aHF acidified with AsF5. Powdered Pd(AsF6)2 slowly loses AsF5 in a dynamic vacuum. It can therefore be isolated from solution at T < 253 K. Single‐crystals of Pd(AsF6)2 were prepared by solvothermal synthesis from a Pd/AsF5/F2/aHF mixture at 393 K. Pd(AsF6)2 is triclinic with a = 500.9(5), b = 538.3(5), c = 864.9(9) pm, α = 74.46(3), β = 89.97(4), γ = 62.47(2)°, V = 0.1972(3) nm3, and Z = 1, space group P$\bar 1$ (No. 2). The six‐coordinate Pd atoms (coordinated with fluorine) are well separated by isolated AsF6 units. In the 2−175 K temperature range Pd(AsF6)2 follows the Curie−Weiss law with μeff = 3.53 B.M., Tn = 8 K and θp= −13 K. Because of cation‐anion interactions, the AsF6− anions deviate from ideal Oh symmetry. The reduced symmetry can be seen in vibrational spectra, where splitting of the anion vibrational modes can be observed. The oxidation of Pd metal or PdO with F2 in neutral aHF yielded Pd2F6. No reaction was observed between Pd, PdO or Pd2F6 and AsF5 in aHF. All attempts to prepare PdFAsF6 were unsuccessful. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)