An electron spin resonance study of the copper(II) chelate of 2-(2′-pyridyimethylenehydrazonomethyl)phenol and related compounds

Abstract

The e.s.r. spectrum due to the copper(II)chelate of 2-(2′-pyridylmethylenehydrazonomethyl)phenol (HL¹) shows that while the chelate is monomeric in N,N-dimethylformamide (dmf) solution at room temperature, dimerization occurs in frozen solution. The absence of dimerization in the copper(II) chelate of the aldazine derived from the reaction of pyridine-2-carbaldehyde with the hydrazone of benzaldehyde implicates the ionized hydroxy group in the dimerization process. Spin-Hamiltonian and structural parameters have been determined by computer simulation of the triplet-state e.s.r. spectrum due to the dimeric species. Monomeric forms of Cu(L¹)₂, occur in dmf solutions containing pyridine, imidazole, 2-methylpyridine, or 2,4,6-trimethylpyridine. Under these circumstances, the superhyperfine lines [from the bonding of copper(II)to four nitrogen atoms from the ligands], observed in the e.s.r. spectra due to the copper(II)chelate in frozen dmf solution containing the heterocyclic nitrogenous base become progressively more difficult to discern in the order pyridine < imidazole < 2-methylpyridine > 2,4,6-trimethylpyridine. Spin-Hamiltonian parameters and linewidth terms have been determined by computer simulation of the e.s.r. spectra due to monomeric forms of the copper(II)chelates where the loss of superhyperfine structure depends on the magnitude of the linewidth terms.