Co-ordination of solvent molecules to square-planar mixed-ligand nickel(II) complexes: a thermodynamic and quantum-mechanical study

Abstract

Equilibria between four-, five- and six-co-ordinated substituted and unsubstituted [Ni(β-dik)(diam)]⁺ complexes associated with various solvents like acetonitrile, acetone, n-butanol, formamide dimethylformamide, dimethyl sulfoxide and pyridine have been investigated in nitroethane solution at 293 K. Increasing donor strength of the donor solvents (L) as well as increasing electron-withdrawing properties of the substituents at the β-diketonate (β-dik) and the diamine (diam) ligands favours the formation of six-co-ordinated species. The results are interpreted using correlations with IR, Hammett and electrochemical data, and results of semiempirical quantum-mechanical calculations carried out within an extended CNDO/2 framework, cis–trans Isomerism is proposed for [Ni(β-dik)(diam)L₂]⁺ due to the mechanism of stepwise co-ordination.