The coordination chemistry and magnetism of compounds derived from formylphenols and diaminomaleonitrile

Abstract

This thesis describes the synthesis~ spectroscopic characterization, electrochemistry and magnetism of mononuclear and polynuclear coordination compounds derived from formylphenols and diaminomaleonitrile (DAM), as well as extended Hückel molecular orbital calculations concerning the magnetic behaviour of binuclear macro cyclic copper(II) compounds. -- Chapter l provides an overview of the literature to date concerning these compounds, with an emphasis on the current understanding of the magnetic properties of binuclear copper(II) systems from experimental (magnetostructural correlations) and computational (extended Hückel and ab initio) points of view. Chapter 2 describes the syntheses of mononuclear and polynuclear copper(II) compounds derived from formylphenols and DAM. A discussion of the x-ray diffraction structures of two copper(II) compounds along with infrared, UV -visible, electrochemical and variable temperature magnetism studies on the DAM-based systems is presented in chapter 3. While copper(II) readily templated the desired DAM-based product, this was not found in general for other metal ion salts and a series of IR guidelines was established to assess the structure and nuclearity of the products isolated. The UV-visible spectra of the copper(II) DAM systems are dominated by charge transfer bands that originate from the 1t framework of the ligand, in contrast to related binuclear copper(II) systems. Cyclic voltammetry revealed that the binuclear copper(II) systems all exhibit a single non-reversible one-electron reduction at uncharacteristically high electrode potentials, except in the case of a diacetonyl adduct (formed upon reaction of a binuclear copper(II) macrocyclic compound with acetone) which undergoes two one-electron reductions to a binuclear copper(I) species via a mixed valence intermediate. The magnetism of the binuclear copper(II) systems is greatly affected by the electronic structure of the DAM residues and this is discussed in detail. The presence of antiferromagnetic exchange in the acetonyl adduct (2J = -25cm⁻¹) despite having the smallest average phenoxide angle reported to date (92.4°) provides experimental support for the results of the extended Hückel study on macrocyclic phenoxide bridged binuclear copper(II) systems.