EPR SPECTROSCOPY AND EXCHANGE INTERACTION PARAMETERS IN CU(GLYCINE)(2)CENTER-DOT-H2O

EPR measurements have been performed in single crystals of Cu(glycine) . H2O, at 9.7 and 33 GHz and at room temperature. This orthorhombic cr ystal has four chemically identical but magnetically non-equivalent co pper ions per unit cell. The EPR data al both microwave frequencies sh ow two partially resolved EPR lines for some of the field directions i n the ab plane, while only a single line is observed along any directi on in the other two crystallographic planes. This indicates that the f our copper ions are arranged in two weakly coupled and symmetry-relate d subsets, each involving two non-equivalent and interacting copper si tes. The decoupling of the spectra leads to g(1) = 2.256(2), g(2) = 2. 071(2) and g(3) = 2.061(2) for the principal values of the molecular g -factors. The EPR data, used in conjunction with the classical Anderso n's model and the Kubo and Tomita's theory, allow to evaluate the exch ange interaction parameters between the magnetically non-equivalent co pper ions. The Anderson's model and the observed EPR line positions da ta lead to \J'/k\ = 19(3) mK for the intersubset exchange coupling. Th e analysis of the angular variation of the line width in terms of the Kubo and Tomita's theory, gives \J'/k\ = 21(2) mK and \J/k\ = 57(1) mK for the intersubset and intrasubset exchange couplings, respectively. These values are discussed in terms of the crystal structure of the c ompound and compared with the results obtained by other authors.