ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated β-diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu2L·2Py (H4L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, aCu = (39—40)·10–4 cm–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the σ-bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, aCu = (55—63)·10–4 cm–1) typical of mononuclear copper complexes.