Mechanism of complexation of nickel(2+) ion in dimethyl sulfoxide and of copper(2+) ion in methanol with monodentate ligands

Abstract

Electrical conductance data for Ni(NCS)2 in DMSO and Cu(C104)2 in MeOH at 25°are reported. They indicate the two electrolytes to be associated in the two solvents with association constants X'níncS'1' = 989 ^' ® DMSO and J^cuClO + = 193 M~' in MeOH. Pressure-jump relaxation kinetic data are reported for Ni(NCS)2 in DMSO at 20, 25, 30, and 35°. ^The analysis of the data reveals the mechanism to be interchange dissociative (Id) with the rate constant of ligand penetration in the first coordination sphere of Ni2+ to be of the same order of magnitude as the pseudo-first-order rate constant for solvent exchange. The activation enthalpy confirms the above. Ultrasonic relaxation data of Cu(C104)2 in MeOH at 25°also indicate the mechanism to be Id with k23 = /rexch. Previous findings in MeOH and DMSO indicating slower rates of substitution are suggested to be due to the structure of the ligand, specifically to the multidenticity of it in the case of previous studies in DMSO. The general validity of the Eigen interchange dissociative mechanism for monodentate ligands is reaffirmed.

Kinetics and Equilibria of Nickel(II)−Schiff Base Adducts Formation

“…Other calculations concerning some species involved in the reaction of Ni II cations with HL ligands were performed in the same way. With the aim to evaluate the [NiS 6 ] 2ϩ /HL (S ϭ solvent) interaction energy of the outer-sphere complex, we resorted to the Fuoss association theory [32,33] (originally developed for ions in a solvent), represented as a polarizable continuum and adapted to the case of an ion interacting with a dipole. If the cation is considered as a point charge at the centre of a sphere of radius a, then the equilibrium constant K 0 can be approximated as in Equation (6), where a is expressed in cm, N is the Avogadro number, and U is the chargeϪdipole electrostatic interaction energy.…”