Kinetics of chloride substitution in the [Pt2(6NNpy)Cl4] complex by L-methionine

Publication date: Available online 14 February 2020Source: Inorganica Chimica ActaAuthor(s): Adrian TopolskiAbstractThe studied platinum(II) complex is an example of bimetallic chlorido complexes. Its reaction with S-donor L-methionine results in substitution of chloride ligand by incoming nucleophile. A possible hydrolysis process is omitted due to addition of chlorides (10 mM) to the reaction mixture. The isosbestic point observed on the spectra of the reaction mixture shows that the studied process is a simple one-step substitution. It is in agreement with a one-exponential behavior of absorbance-time data. Dependency of the observed rate constant on L-methionine concentration is linear with non-zero intercept suggesting reversibility of the process. Activation parameters, i.e. positive ΔH≠ and strongly negative ΔS≠, suggest associative path of the forward and reverse reactions what is expected for substitution in square-planar platinum(II) complexes. The studied complex reacts with L-methionine faster than its quinoline analogue. It results from steric hindrances in the reaction of the latter complex as well as from higher electrophilicity of platinum(II) center in the [Pt2(6NNpy)Cl4] complex, described in this paper. The opposite tendency is observed for the reverse process. It can be explained taking into account lower stability of the quinoline complex with L-methionine than its pyridine analogue.Graphical abstract

Source: Inorganica Chimica Acta - February 14, 2020 Category: Chemistry Source Type: research