Structural and magnetic properties of a copper–amino acid salt: Copper (II) bis (α-amino isobutyrato)

Abstract

The copper salt of the amino acid α-amino isobutyric acid was synthesized and the crystal structure was determined by x-ray techniques. The crystals are monoclinic, space group P21/c (Z=2) with a=10.470(3) Å, b=5.335(1) Å, c=10.201(3) Å, and β=115.6(2)°. The magnetic susceptibility, measured between 1.4 and 12 K, shows a Curie–Weiss behavior with antiferromagnetic Curie temperature Tc =0.66 K. These data and a simple mean field argument which assumes equal superexchange pathways between Cu nearest neighbors gives J≂0.22 K (antiferromagnetic) for the exchange coupling constant between copper ions. The gyromagnetic factor g and the linewidth ΔH of the single exchange narrowed EPR line were measured as a function of the orientation of the applied magnetic field at room temperature. The gyromagnetic tensor reflects the molecular properties of the square planar Cu(II) complex and the orientation of these molecules within the unit cell of the crystal. The observed magnitude and angles variation of ΔH is analyzed in terms of the exchange narrowed dipolar and hyperfine linewidth. An estimate of the exchange coupling constant from the observed narrowing of the hyperfine broadening support the value obtained from the susceptibility data. Since the exchange parameter J obtained by assuming exchange narrowing of the dipolar linewidth is three times smaller than that obtained from the susceptibility data, we suggest the possibility of a quasi-two-dimensional magnetic behavior, which is supported by our crystallographic data.