Exchange Interaction Between Copper(II) Ions Through Glutamic Acid Molecules

C. D. BRONDINO,; N. M. C. CASADO; M. C. G. PASSEGGI, ; R. CALVO

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Año: 1993 vol. 32 p. 2078 - 2084

0020-1669

EPR measurements at wo = 9.7 and 33.3 GHz microwave frequencies in single crystals of the copper complex of glutamic acid [Cu(glu)] and at 9.8 GHz in the zinc complex of glutamic acid [Zn(glu)] doped with 63Cu have been performed at room temperature. A single EPR line was observed in Cu(g1u) for any orientation of the magnetic field B at both frequencies. The gyromagnetic tensor exhibits axial symmetry, and the line width AB,,(&$) is strongly dependent on 00. We calculate the dependence of the line width with wo in terms of the exchange interactionsbetween the copper ions. This is achieved with a model based on Kubo and Tomita’s theory, which allows us to evaluate selectively the exchange coupling constants 14 between nonequivalent copper ions in the unit cell. Pathways for superexchange between copper ions in Cu(g1u) are provided by carboxylate bridges and hydrogen bonds, as well as by glutamic acid units. From the data we estimate IJ,I = 0.19 K between copper ions in a distorted octahedral coordination, connected equatorially through the u skeleton of a glutamic acid molecule. This bridge involves sixdiamagnetic atoms. A lower limit for the exchange parameter assigned to the carboxylate paths is estimated as JJ,I > 1 K. The results obtained for Zn(g1u) doped with 63Cu are used to study the electronic properties of the isolated copper ions, which in turn allow one to understand the overall axial symmetry of the g2 tensor, and the line width data obtained in Cu(g1u).