EPR study of Cu(II) dopant ions in single crystals of bis(L-asparaginato)Zn(II)

Abstract

We report an electron paramagnetic resonance (EPR) study at 33.9 GHz and room temperature of oriented single crystal samples of bis(Lasparaginato) Zn(II) doped with Cu(II). The variation of the spectra with magnetic field orientation was measured in three crystal planes (a*b, bc and a*c, with a*Zb!c). These spectra display two groups of four peaks arising from the hyperfine interaction with the ICuZ3/2 nuclear spins of copper. They were assigned to Cu(II) ions in two lattice sites related by a 1808 rotation around the b-crystal axis. The g and hyperfine coupling (A) tensors of the Cu(II) ions were evaluated from the single crystal data. Some indeterminacy in the assignment of the signals was avoided measuring the EPR spectrum of a powder sample. Their principal values are g1Z2.060(1), g2Z2.068(2), g3Z2.283(2), and A1z0.1!10K4, A2Z13!10K4 and A3Z165!10K4 cmK1. The eigenvectors corresponding to g3 and A3 are coincident within the experimental error; the other eigenvectors are rotated 5.68 in the perpendicular plane. Considering the crystal structure of bis(L-asparaginato)Zn(II), our EPR results indicate that the Cu(II) impurities replace Zn(II) ions in the host crystal. We propose a molecular model based on the EPR data and the structural information, and analyse the results comparing the measured values with those obtained in similar systems. q 2005 Elsevier Ltd. All rights reserved.