Base hydrolysis kinetics and equilibria of [bis(2-pyridylmethyl)amine]chloroplatinum(II) and crystal and molecular structures of [Pt(bpma)Cl]Cl•H2O and [Pt(bpma)(OH2)](ClO4)2•2H2O

The kinetics of base hydrolysis of [Pt(bpma)Cl]Cl [bpma = bis(2-pyridylmethyl)amine] have been studied (5 x 10(-4) < [OH-] less than or equal to 0.2 mol dm(-3)) at 25 degreesC and I = 0.2 mol dm(-3) by UV-Vis spectrophotometry. The derived rate law is consistent with a mechanism involving a rapid preequilibrium between the substrate [Pt(bpma)Cl](+) and the amido species [Pt(bpmaH(-1))Cl] (pK(a1) = 12.3) followed by slow solvolysis to give the corresponding aqua species [Pt(bpma)(OH2)](2+) [k(s) = (2.8+/-0.2) x 10(-4) s(-1)] and [Pt(bpmaH(-1))(OH2)](+) [k(s)' = (3.28+/-0.02) x 10(-3) s(-1)] which undergo deprotonation and are converted to unreactive hydroxo, species. The aqua complex [Pt(bprna)(OH2)](ClO4)(2).2H(2)O, independently isolated in the solid, behaves as a dibasic acid in water solution(25 degreesC, I = 0.2 mol dm(-3)), the two ionization constants being related to the dissociation of the water molecule in the aquo-amine (pK(1) = 5.4+/-0.1) and of the amino group in the hydroxo-amino species (pK(2) = 11.5+/-0.1), respectively. The X-ray crystal structures of [Pt(bpma)Cl]Cl.H2O and [Pt(bpma)(OH2)](ClO4)(2).2H(2)O are reported. (C) 2002 Elsevier Science Ltd. All rights reserved.