Reaction of Palladium(II) Salts with Cerium(III) Salts in Acetic Acid

Abstract

Formation of complexes between Pd(II) salts and Ce(II) salts in acetic acid asstudied by means of UV spectrophotometry.On addition of cerous acetate Ce(0Ac)3 to palladous acetate Pd(OAc)2 solution, a strong absorption band with a maximum at 342 nm appeared (Fig.1). The dependence of the ab-sorbance at 342 nm upon the molar ratio of Pd(II)Ce(III) suggested the formation of an equi-molar complex of Pd(OAc)2 and Ce(0Ac)3 (Fig.2). The equilibrium constant K, for the reaction was about 104.8(1/mol) at 25° C.Addition of water or lithium acetate to the system caused an increase in the reaction rate(Fig.5, Fig.9), and a decrease in the equilibrium concentration of the complex (Fig.6, Fig.8). These facts suggest that the complex is formed mainly through two successive reactions: (1) formation of a intermediate X+Pd(OAc)3-from Pd(OAc)2, (where X+ denotes Li+, H3 0+, or Hsup 0Ac+), (2) reaction of theintermediate with Ce(0Ac)3. The kinetic data were found to beconsistent with theabove assumption.In the presence of HCI, addition of Ce(OAc)3 did not change the absorption spectrum of the Pd(II) solution, but brown crystals with the composition of [PdCe(OAc)2 Cl3, 3H2 O]were separated from thesolution. Far-IR spectrum of the crystal suggests the complex has a chloride-bridged structure.