Magnetic properties and EPR spectra of [Cu(L-arginine)(2)](NO3)(2)center dot 3H(2)O

GERARD, M. F.; AIASSA, C.; CASADO, N. M. C.; SANTANA, R. C.; PEREC, M.; RAPP, R. E.; CALVO, R.

Journal of Physics and Chemistry of Solids

Elsevier

Año: 2007 vol. 68 p. 1533 - 1539

0022-3697

Magnetic and EPR data have been collected for complex [Cu(L-Arg)(2)](NO3)(2).3H(2)O (Arg = arginine). Magnetic susceptibility chi in the temperature range 2-160 K, and a magnetization isotherm at T = 2.29(l) K with magnetic fields between 0 and 9 T were measured. The observed variation of chi T with T indicates predominant anti ferromagnetic interactions between Cu(II) ions coupled in ID chains along the h axis. Fitting a molecular field model to the susceptibility data allows to evaluate g = 2.10(l) for the average g-factor and J = -0.42(6) cm(-1) for the nearest neighbor exchange coupling (defined as H-ex = -Sigma J(ij)S(i) . S-j). This coupling is assigned to syn-anti equatorial-apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682 A, with a total bond length of 6.989 angstrom and is consistent with the magnetization isotherm results. It is discussed and compared with couplings observed in other compounds with similar exchange bridges. EPR spectra at 9.77 were obtained in powder samples and at 9.77 and at 34.1 GHz in the three orthogonal planes of single crystals. At both microwave frequencies, and for all magnetic field orientations a single signal arising from the collapse due to exchange interaction of resonances corresponding to two rotated Cu(II) sites is observed. From the EPR results the molecular g-tensors corresponding to the two copper sites in the unit cell were evaluated, allowing an estimated lower limit J > 0. 1 cm(-1) for the exchange interaction between Cu(II) neighbors, consistent with the magnetic measurements. The observed angular variation of the line width is attributed to dipolar coupling between Cu(II) ions in the lattice.