Spectral and electrochemical behaviour of some copper(II) complexes with CuO₄ chromophore

Abstract

A few mixed ligand complexes of the type Cu(TCA)(L) [where TCA = trichloroacetic acid; L=2, 2, 6, 6-tetramethyl-3, 5-heptanedione (DPM), 2, 6-dimethyl-3, 5-heptanedione (DMHD) and <i>o-</i> hydroxybenzophenone (OHBP)] have been prepared and characterised by IR, electronic and EPR spectral data and compared with those of the corresponding CuL₂ and other Cu(TCA)(L) chelates [where L=acetylacetone (ACAC), ethylacetoacetate (EAA), salicylaldehyde (SAL) and <i>o</i>-hydroxyacetophenone (OHAP)] to illustrate the nature of bonding of TCA with Cu(II). The Cu^ll/Cu^I redox potentials of the bis-chelates vary in the order, DPM < DMHD < ACAC < EAA; SAL <img src='/image/spc_char/wave.gif' border=0> OHAP < OHBP; they shift towards more negative values as the number of electron repelling methyl groups increases. For mixed ligand complexes, the potentials are more positive than those of their respective bis-complexes and vary in the order, DPM > DMHD > ACAC > EAA: SAL < OHAP < OHBP. All the above results suggest that the replacement of L in CuL₂ by TCA leads to a decrease in the delocalisation of electron density, more in <i>o</i>-hydroxyarylcarbonyl rather than in <i>β</i>-diketonate complexes.