Magnetic interactions in aqua( l-aspartato)-(2,2′-bipyridine)copper(II) trihydrate

Abstract

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-aspartato)(2,2′-bipyridine)copper(II) 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 tensor is nearly diagonal and axially symmetric, in agreement with the crystal structure. The linewidth ΔB PP(≡, φ) 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∥ ≈ ∥ J c∥ ≈ ∥ 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.