COORDINATION OF SOLVENT MOLECULES TO SQUARE-PLANAR MIXED-LIGAND NICKEL(II) COMPLEXES - A THERMODYNAMIC AND QUANTUM-MECHANICAL STUDY

Equilibria between four-, five- and six-co-ordinated substituted and u nsubstituted [Ni(beta-dik)(diam)]+ complexes associated with various s olvents like acetonitrile, acetone, n-butanol, formamide dimethylforma mide, dimethyl sulfoxide and pyridine have been investigated in nitroe thane solution at 293 K. Increasing donor strength of the donor solven ts (L) as well as increasing electron-withdrawing properties of the su bstituents at the beta-diketonate (beta-dik) and the diamine (diam) li gands favours the formation of six-co-ordinated species. The results a re interpreted using correlations with IR, Hammett and electrochemical data, and results of semiempirical quantum-mechanical calculations ca rried out within an extended CNDO/2 framework. cis-trans Isomerism is proposed for [Ni(beta-dik)(diam)L2]+ due to the mechanism of stepwise co-ordination.