Palladium(II) Complexes Compounds with L-Threonine and Cytosine

The palladium(II)-L-threonine(cytosine)-water and palladium(II)-L-threonine-cytosine-water systems are studied by pH-metric titration. The formation constants of complexes with Pd(II) : Thr = 1 : 1 and 1 : 2 (logK1 = 6.91 and logK2 = 4.09); Pd(II) : Cyt = 1 : 1 and 1 : 2 (logK1 = 10.68 and logK2 = 8.66), as well as the mixed-ligand complexes Pd(II) : Thr : Cyt = 1 : 1 : 1 (logβ = 18.79), are determined. The Pd(ThT)Cl2 · H2O, Pd(Thr)2Cl2, Pd(Cyt)Cl2 · H2O, Pd(Cyt)2Cl2, and Pd(Thr)(Cyt)Cl2 complexes are synthesized by reacting H2PdCl4 aqueous solution and organic reagents. The IR spectra (400-4000 cm-1) point to the coordination of threonine to palladium(II) through the amino group; and cytosine, through the nitrogen-3 atom of the heterocycle. Thermolysis of these compounds leads first to PdO at ∼ 540°C and then to metallic palladium at temperatures higher than 780°C.