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 crystal has four chemically identical but magnetically non-equivalent copper ions per unit cell. The EPR data al both microwave frequencies show two partially resolved EPR lines for some of the field directions in the ab plane, while only a single line is observed along any direction in the other two crystallographic planes. This indicates that the four copper ions are arranged in two weakly coupled and symmetry-related subsets, each involving two non-equivalent and interacting copper sites. 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 Anderson's model and the Kubo and Tomita's theory, allow to evaluate the exchange interaction parameters between the magnetically non-equivalent copper ions. The Anderson's model and the observed EPR line positions data lead to \J'/k\ = 19(3) mK for the intersubset exchange coupling. The 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 compound and compared with the results obtained by other authors.