Electron spin resonance study of dimer formation by copper(II) chelates of hydroxybenzoic acids

Abstract

Experimental evidence produced by e.s.r. measurements at room temperature and 77 K shows that the formation of dimeric species by combination of copper(II) with substituted o-hydroxybenzoic acids is influenced by the other functional groups in the aromatic ring. The ligands used include 5-chlorosalicylic acid, p-aminosalicylic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid. The effect of other structural variations was studied by using 3,5-dihydroxybenzoic acids, salicylamide, and o-phthalic acid. The relevant e.s.r. spectra have been dealt with by consideration of a spin-Hamiltonian for the paramagnetic states in the dimeric species. In the case of dimer formation, the spectra may arise from dipole–dipole interactions between the copper(II) ions and/or from exchange. The magnetic parameters associated with the spectra due to dimeric species have been determined by comparison of computer-simulated and experimental spectra.