Thermodynamic, kinetic and structural studies on the mixed ligand complexes of palladium(II) with tridentate and monodentate ligands

Stability constants of the complexes formed in the reaction of [Pd(bpma)](2+) [bpma=bis(pyridin-2-ylmethyl)amine] with monodentate nitrogen and thioether ligands including uridine, MeUH, cytidine, MeC, EtGH, AcHis, AcHm, AcLys and AcMet were determined by potentiometric method. The coordination chemistry of [Pd(bpma)](2+) shows a significant similarity to that of [Pd(terpy)](2+), but it is different from [Pd(dien)](2+). The formation of hydroxo and dinuclear complexes is especially enhanced in the case of [Pd(bpma)](2+) and [Pd(terpy)](2+), but the affinity of palladium(II) ions for the coordination of thioether residues is reduced in the presence of pyridine nitrogen atoms. Stopped-flow kinetic measurements reveal that the substitution reactions of the thioether ligand AcMet are much faster than those of the N-donor cytidine. The presence of the two pyridyl residues significantly enhances the kinetic reactivity of [Pd(bpMa)](2+) as compared to that of [Pd(dien)](2+). The Pd-S(thioether) bonded species can be important intermediates in multicomponent systems, but the equilibrium state is characterised by the formation of Pd-N bonded species. The complex [Pd(bpma)NO3]NO3 has been prepared in solid state and its structure was elucidated by single crystal X-ray diffraction method. (C) 2003 Elsevier Science Inc. All rights reserved.