EPR study of weak exchange interactions in binuclear copper(ii) complexes with salicylaldehyde acyldihydrazones

Abstract

The binuclear CuII complexes with bis(salicylidene)hydrazones of dicarboxylic acids and their analogs (H4L) of composition [Cu2L·2Py] in which the coordination polyhedra are linked by a polymethylene chain containing from one to eight CH2 units were studied by EPR spectroscopy. Weak antiferromagnetic spin-spin exchange interactions between two CuII atoms were found in the complexes based on hydrazones of malonic, succinic, glutaric, and adipic acids. These exchange interactions are manifested in the EPR spectra of liquid solutions as seven-line hyperfine signals from two equivalent CuII atoms with the hyperfine coupling constant a Cu ≈ 40·10–4 cm–1. The exchange ceases as the length of the polymetylene chain increases to five-eight units and the EPR spectra show a four-line signal with a Cu ≈ 80·10–4 cm–1 typical of mononuclear complexes.