Synthesis and spectroscopic studies on novel Cu(II)–Cu(II) binuclear adducts. EPR evidence for ferromagnetic interactions

EPR investigations on two solid complexes [Cu(1-amidino-O-2-methoxyethylurea)2]2(H2O)2(SO4)2 (1) and [Cu(1-amidino-O-2-ethoxyethylurea)2]2(H2O)2(SO4)2 (2) indicated the formation of ferromagnetically coupled binuclear complexes (S = 1) having the isotropic exchange interaction constant J values of 59 and 50 cm−1. The angle between the Cu–Cu direction and the parallel direction (ξ) of the complex 1 has been evaluated. The IR studies suggest the presence of tetrahedral sulfate ion in the complexes. When the EPR spectra were recorded in the temperature range 300–475 K, it was observed that the triplet-state EPR signal disappeared completely and irreversibly at ca. 450 K for complex 1 and at ca. 475 K for complex 2 with the appearance of a new signal attributable to the mononuclear complex (S = 1/2).