MAGNETIC-INTERACTIONS IN AQUA(L-ASPARTATO)-(2,2'-BIPYRIDINE)COPPER(II) TRIHYDRATE

We report magnetic susceptibility measurements in polycrystalline samples and EPR measurements at X-band in single crystal samples of the ternary complex of copper with aspartic acid and bipyridine, aqua(L-aspartaro)(2,2'-bipyridine)copper trihydrate, Cu(asp)bpy. This compound exhibits a layered structure for the copper ions. Within each layer, these ions are connected by a chemical path that involves a carboxylate bridge and a hydrogen bond, and by the stacking of the aromatic rings of the bipyridyl ligands. They provide the pathways for magnetic superexchange. Magnetic susceptibility data indicate a weakly ferromagnetic Curie-Weiss behavior in the studied temperature range (2-300 K), and molecular field theory gives J/k(B)=0.12(4) K for the mean value of the exchange parameter between copper ions. We observed a single exchange collapsed EPR line in Cu(asp)bpy for any orientation of the magnetic field. The g tenser is nearly diagonal and axially symmetric, in agreement with the crystal structure. The linewidth Delta B-pp(theta,phi) exhibits a behavior characteristic of a two-dimensional system, which originates in the layered structure of Cu(asp)bpy. From the EPR data we estimate \J\=\(J(C)+J(B))/2\approximate to\J(C)\approximate to\J(B)\=0.20(3) K, where J(C) is the exchange parameter associated with the chemical path involving the carboxylate bridge and the hydrogen bond, and J(B) is that associated with the stacking of the bipyridyl ligands. There is a reasonable agreement between the exchange parameters obtained from susceptibility and EPR measurements. The J(B) value indicates that the stacking of the aromatic rings may act as a sizeable exchange interaction path.