Kinetic Study on the Formation of Platinum-Blue Complexes with Oxygen

A kinetic study of Pt-blue complex formation was carried out in a solution containing [Pt (NH3)2 (H2O)2]2+ and uracil under oxygen bubbling, with monitoring by means of an oxygen analyzer and visible spectrometer. The rate of oxygen consumption was first-order with respect to concentration of [Pt (NH3)2 (H2O)2]2+, uracil, or oxygen. A correlation was found between the decrease of oxygen consumption in the solution and the increase of the absorbance at 640 nm, namely formation of the blue complex. The formation mechanism of the blue complex is considered to be 1) first the equilibrium reaction of the coordination of uracil to Pt, 2) next the oxidation of the Pt-uracil complex with oxygen, and 3) finally a follow-up reaction presumably via formation of polynuclear complexes. Eight other blue complexes were formed by the use of N-aromatic base ligands possessing an amide linkage. The oxygen consumption rates of these complexes were found to be large in the case of the ligands which form many structurally isomeric complexes.