MAGNETIC-INTERACTIONS IN THE COPPER COMPLEX (L-ASPARTATO)(1,10-PHENANTHROLINE)COPPER HYDRATE - AN EXCHANGE-COUPLED EXTENDED SYSTEM WITH 2 DISSIMILAR COPPER IONS

We report EPR measurements in single-crystal samples at the microwave frequencies 9.8 and 34.3 GHz and magnetic susceptibility measurements in polycrystalline samples for the ternary complex of copper with aspa rtic acid and phenanthroline, (L-aspartato)(1,10-phenanthroline)copper hydrate. The crystal lattice of this compound is composed of two diss imilar copper ions identified as Cu(A) and Cu(B), which are in two typ es of copper chains called A and B, respectively, running parallel to the b crystal axis. The copper ions in the A chains are connected by t he aspartic acid molecule, and those in the B chains by a chemical pat h that involves a carboxylate bridge and a hydrogen bond, Both chains are held together by a complex network of hydrogen bonds and by hydrop hobic interactions between aromatic amines. Magnetic susceptibility da ta indicate a Curie-Weiss behavior in the studied temperature range (2 -300 K). The EPR spectra at 9.8 GHz display a single exchange collapse d resonance for any magnetic field orientation,in the so-called strong exchange regime. Those at 34.3 GHz are within the so-called weak exch ange regime and display two resonances which belong to each type of co pper ion chain. The decoupling of the spectra at 34.3 GHz using a theo ry based on Anderson's model for the case of two weakly exchange coupl ed spins S = 1/2 allows one to obtain the angular variation of the squ ares of the g-factor and the peak-to-peak line width of each resonance . This model also allows one to evaluate the exchange parameter \J(AB) /k\ = 2.7(6) mK associated with the chemical path connecting dissimila r copper ions, The line width data obtained for each component of the spectra at 34.3 GHz are analyzed in terms of a model based on Kubo and Tomita's theory, to obtain the exchange parameters \J(A)/k\ = 0.77(2) K and \J(B)/k\ = 1.44(2) K associated with the chemical paths connect ing the similar copper ions of types A and B, respectively.