Calculations of microconstants and equilibrium formation constants for platinum(II) and palladium(II) halide complexes in solution

Abstract

Distribution diagrams and formation functions for halide complexes [M(H2O)4 − nCln]2 − n (M = Pt(II) or Pd(II)) and [PdCl4 − nBrn]2− (n = 0–4) in solution are analyzed in terms of the matrix model. Equilibrium constants for binding the first ligand \(\left( {\bar K} \right)\) and corrections for the mutual influence between ligands (ω) in the course of complex formation in solution are calculated. In examples analyzed, the substitution of chloride ion for water in the coordination sphere of platinum(II) and palladium(II) is an anti-cooperative process. The substitution of bromide ion for chloride ion in the coordination sphere of [PdCl4]2− is weakly cooperative. Quantum-chemical calculations show that platinum(II) and palladium(II) cis-bisaquadichloro complexes in the gas phase are thermodynamically less stable than trans-isomers. The cis-trans isomerization constants in the gas phase calculated by the DFT method and those found for solutions using the matrix model have the same order of magnitude.