Kinetics of chloride substitution in [Pt(bpma)Cl]⁺ and [Pt(gly-met-S,N,N)Cl] complexes by thiourea, nitrites, and iodides

Abstract

Substitution of chloride in [PtCl(bpma)]+ and [PtCl(gly-met-S,N,N)], where bpma is bis(2-pyridylmethyl)amine and gly-met-S,N,N is glycyl-l-methionine, was studied as a function of the entering nucleophile concentration and temperature. Reactions between the platinum(II) complexes and thiourea (TU), iodides (I-), and nitrites(III) (NO 2-) were carried out in aqueous solutions using conventional UV-VIS spectrophotometry. Suitable ionic conditions were reached by an addition of 0.1 M NaClO4 and 0.01 M NaCl (to suppress hydrolysis). The second-order rate constants, k 2, for the studied reactions with NO 2- varied between 0.036-0.038 M-1 s-1, and for the reactions with TU between 0.095-1.06 M-1 s-1, respectively. The reaction between TU and the [PtCl(bpma)]+ ion is ten times faster than that of the [PtCl(gly-met-S,N,N)] complex. An analysis of the activation parameters, ΔH ≠ and ΔS ≠, for the selected reactions clearly shows their associative nature. © 2013 Institute of Chemistry, Slovak Academy of Sciences.