Crystal structures and pressure-induced redox reaction of Cs2PdI4.I2 to Cs2PdI6

Two iodopalladates of the same empirical formula with palladium in different oxidation states were synthesized from aqueous HI solution. Their crystal structures were characterized by single-crystal X-ray analysis, and the effect of hydrostatic pressure on the structural properties has been investigated. Dicesium hexaiodopalladate(IV), Cs2PdI6, crystallizes in a cubic system, space group Fm3m, with a = 11.332(1) A and Z = 4, and is isotypic to K2PtCl6. The second compound, dicesium tetraiodopalladate(II) diiodine, Cs2PdI4.I2, shows tetragonal symmetry with space group I4/mmm, a = 8.987(1) A, c = 9.240(1) A, and Z = 2. The crystal structure can be described in resemblance to the Cs2Au(I)Au(III)Cl6 type. Structural relationships and chemical and structural transformation between both compounds will be discussed. DTA measurements at ambient pressure showed liberation of I2 and decomposition of the compounds. Cs2PdI4.I2 represents an excellent example for studying a solid-state electron-transfer reaction. The redox reaction to Cs2PdI6 can be demonstrated by performing pressure-dependent X-ray studies.