Kinetics and Mechanism of Interaction of Thiosemicarbazide with Di-μ-hydroxobis(1,10-phenanthroline) Dipalladium(II) Perchlorate in Aqueous Solution

Abstract

The kinetics and mechanism of the interaction between thiosemicarbazide with di-μ-hydroxobis(1,10-phenanthroline)dipalladium(II) ion complex has been followed spectrophotometrically in pseudo first order conditions in aqueous solution as a function of [Pd(1,10-phen)(H2O)2]2+, [thiosemicarbazide], pH, and temperature. The reaction of thiosemicarbazide (TSC) at pH 6.5 has been monitored at 240 nm. The reaction rate increases linearly with increasing thiosemicarbazide concentration in the studied concentration range. The second order rate constants 102k2 are 27.01, 33.78, 40.23, and 50.46 dm3 mol−1 s−1 at 20, 25, 30, and 35○C, respectively, have been calculated from the slope of k versus [thiosemicarbazide] plot by using the Origin6.0 software. From the experimental findings, an associative mechanism for the substitution reaction is proposed. The activation parameters calculated from Eyring equation are ΔH# 1= 46.72 ± 1.8 kJ mol−1, ΔS# 1= −100.38 ± 3.1JK−1mole−1support the proposition. On the basis of the kinetic and activation parameters, an associative mechanism is proposed for the interaction process. Quantum chemically obtained structures and geometrical parameters of the Pd(II) complex have been reported.