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

We report magnetic susceptibility measurements in polycrystalline samp les and EPR measurements at X-band in single crystal samples of the te rnary complex of copper with aspartic acid and bipyridine, aqua(L-aspa rtaro)(2,2'-bipyridine)copper trihydrate, Cu(asp)bpy. This compound ex hibits a layered structure for the copper ions. Within each layer, the se ions are connected by a chemical path that involves a carboxylate b ridge and a hydrogen bond, and by the stacking of the aromatic rings o f the bipyridyl ligands. They provide the pathways for magnetic supere xchange. Magnetic susceptibility data indicate a weakly ferromagnetic Curie-Weiss behavior in the studied temperature range (2-300 K), and m olecular 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 held. The g tenser is nearly diagonal and axially symmetric, in agreem ent with the crystal structure. The linewidth Delta B-pp(theta,phi) ex hibits a behavior characteristic of a two-dimensional system, which or iginates 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 che mical path involving the carboxylate bridge and the hydrogen bond, and J(B) is that associated with the stacking of the bipyridyl ligands. T here is a reasonable agreement between the exchange parameters obtaine d from susceptibility and EPR measurements. The J(B) value indicates t hat the stacking of the aromatic rings may act as a sizeable exchange interaction path.