Oxoanionic Noble Metal Compounds from Fuming Nitric Acid: The Palladium Examples Pd(NO₃)₂and Pd(CH₃SO₃)₂

The oxidation of elemental palladium at 100 °C in a mixture of fuming nitric acid and a pyridine-SO3 complex leads to the anhydrous nitrate Pd(NO3)2 (monoclinic, P2(1)/n, Z=2, a=469.12(3) pm, b=593.89(3) pm, c=805.72(4) pm, β=105.989(3)°, V=215.79(2) Å(3)). The Pd(2+) ions are in square-planar coordination with four monodentate nitrate groups which are connected to further palladium atoms, leading to a layer structure. The reaction of elemental palladium with a mixture of fuming nitric acid and methanesulfonic acid at 120 °C leads to single crystals of Pd(CH3SO3)2 (monoclinic, P2(1)/n, Z=2, a=480.44(1) pm, b=1085.53(3) pm, c=739.78(2) pm, β=102.785(1)°, V=376.254(17) Å(3)). Also in this structure the Pd(2+) ions are in square-planar coordination with four monodentate anions; however, the connection to adjacent palladium atoms leads to a chain-type structure. The thermal decomposition of the compounds has been investigated by means of DSC/TG measurements. Furthermore, IR and Raman spectra have been recorded, and an assignment of the observed vibrational frequencies has been carried out based on theoretical investigations.