Abstract

2-Hydroxy-5-methyl-3-methylsulfanylbenzaldehyde(HL2) and 2-hydroxy-5-methyl-3-methylselanylbenzaldehyde (HL3) have been synthesized from 2-hydroxy-5-methylbenzaldehyde (HL1), as have Schiff bases HL4R and HL5R (R = Me or Ph) derived from RNH2 and HL1 or HL2 respectively. The complexes Cu(L)(TpPh) (L1- = L1-, 1; L2-, 2; L3-, 3; L4Me-, 4; or L4Ph-, 5) have been prepared. Single crystal structure determinations of 1, 2, 4 and 5 show copper(II) centres with square pyramidal CuN3O2 (1, 2) or CuN4O (4, 5) co-ordination spheres; for 4 and 5 the basal plane of the complex is twisted by 20-25° because of the steric properties of the Schiff base Me or Ph substituent. The UV/vis and EPR spectra of 1-5 in CH2Cl2 show the presence of tetragonal copper(II) centres. Cyclic voltammograms of 1-5 and the uncomplexed phenols in CH2Cl2-0.5 M Bu4nNPF6 exhibit an irreversible or (for 2) reversible 1-electron oxidation to a phenoxyl radical. The oxidation potentials of HL2 and HL3, and of 2 and 3, are barely distinguishable. However, the irreversibility of this process for 3 compared to that of 2 suggests that a selenoether substituent kinetically stabilises the phenoxyl unpaired spin less efficiently than a thioether one; this is borne out by EHMO calculations on L1�-L3�. Spectroelectrochemical characterisation of 2+, whose UV/vis/NIR spectrum is very similar to that of galactose oxidase, confirms its formulation as the antiferromagnetically coupled species CuII(L2�)(TpPh)+.