Magnetic properties and EPR spectra of [Cu(L-arginine)2](NO3)2 3H2O

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

Año: 2007

0022-3697

Abstract Magnetic and EPR data have been collected for complex [Cu(L-Arg)2](NO3)2 3H2O (Arg = arginine). Magnetic susceptibility w in the temperature range 2–160 K, and a magnetization isotherm at T = 2.29(1)K with magnetic fields between 0 and 9 T were measured. The observed variation of wT with T indicates predominant antiferromagnetic interactions between Cu(II) ions coupled in 1D chains along the b axis. Fitting a molecular field model to the susceptibility data allows to evaluate g = 2.10(1) for the average g-factor and J = -0.42(6) cm1 for the nearest neighbor exchange coupling (defined as Hex = PJijSi Sj). This coupling is assigned to syn–anti equatorial–apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682A ˚ , with a total bond length of 6.989A ˚ 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 34.1GHz 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 |40.1 cm1 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. 2007 Published by Elsevier Ltd.2](NO3)2 3H2O (Arg = arginine). Magnetic susceptibility w in the temperature range 2–160 K, and a magnetization isotherm at T = 2.29(1)K with magnetic fields between 0 and 9 T were measured. The observed variation of wT with T indicates predominant antiferromagnetic interactions between Cu(II) ions coupled in 1D chains along the b axis. Fitting a molecular field model to the susceptibility data allows to evaluate g = 2.10(1) for the average g-factor and J = -0.42(6) cm1 for the nearest neighbor exchange coupling (defined as Hex = PJijSi Sj). This coupling is assigned to syn–anti equatorial–apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682A ˚ , with a total bond length of 6.989A ˚ 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 34.1GHz 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 |40.1 cm1 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. 2007 Published by Elsevier Ltd. Keywords: D. Magnetic properties; D. Electron paramagnetic resonanceD. Magnetic properties; D. Electron paramagnetic resonance