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Kinetic and mechanistic studies on the interaction between azide and cis-diaqua-chloro-tris-(dimethyl sulfoxide)-ruthenium(II) complex in aqueous medium

Alak K.Ghosh, Arup Mandal, Biplab K.Bera, Subhasis Mallick, Subala Mondal, Parnajyoti Karmakar

The kinetics of interaction between azide and cis-[RuCl(Me2SO)3(H2O)2]+ have been studied spectrophotometrically as a function of[RuCl(Me2SO)3(H2O)2 +], [azide] and temperature at a particular pH(5.0),where the substrate complex exists predominantly as a diaqua species(in aqueous solution) and azide as the monoanionic species. The reaction has been found to proceed via two distinct consecutive steps i.e., it shows a non-linear dependence on the concentration of azide: both processes are [ligand] dependant. The rate constants for the processes are: k1 ~ 10-3 s- 1 and k2~ 10-5 s-1. The activation parameterswere calculated fromEyring plots suggest an associative mechanismfor the interaction process. From the temperature dependence of the outersphere association equilibrium constants, the thermodynamic parameters were also calculated, which gives a negative Gï‚° value at all temperature studied, supporting the spontaneous formation of an outersphere association complex.