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

The binuclear Cu-II complexes with bis(salicylidene)hydrazones of dicarboxy lic 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 antiferromagn etic spin-spin exchange interactions between two Cull atoms were found in t he complexes based on hydrazones of malonic, succinic, glutaric, and adipic acids. These exchange interactions are manifested in the EPR spectra of li quid solutions as seven-line hyperfine signals from two equivalent Cu-II at oms with the hyperfine coupling constant a(Cu) approximate to 40 (.) 10(-4) cm(-1). The exchange ceases as the length of the polymetylene chain increa ses to five-eight units and the EPR spectra show a four-line signal with a( Cu) approximate to 80 (.) 10(-4) cm(-1) typical of mononuclear complexes.