Studies of some ternary complexes of copper(II) involving π-bonding ligands

Abstract

The formation constants of complexes of the type [CuAL]⁺, where A = 1, 10-phenanthroline, 2-(2′-pyridyl)benzimidazole, or 2-(2′-pyridyl)imidazoline and = MeCOCH₂CONPh^–(L¹), MeCOCH₂CONC₆H₄OMe-o^–(L²), MeCOCH₂CONC₆H₄Me-o^–(L³), or PhCOCH₂CONPh^–(L⁴), have been determined in dioxan–water (1 : 1 v/v)solutions and 0.1 mol dm^–3 Na[ClO₄] at 30 °C. The value of Δ log K= log K_MAL′–log K_ML is positive (K_MAL′ is for MA + L ⇌ MAL) except when A is 2-(2′-pyridyl)imidazoline. Ultraviolet spectral studies of these complexes have also been carried out and show that there is no significant interaction between the two ligands through the metal d_π orbitals in the mixed-ligand complexes. Positive Δ log K values may be due to a lowering in repulsion between metal d_π electrons and ligand π electrons in the mixed-ligand complex.