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

Abstract

Abstract We report an electron paramagnetic resonance (EPR) study at 33.9 GHz and room temperature of oriented single crystal samples of bis( l -asparaginato)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 *= b × c ). These spectra display two groups of four peaks arising from the hyperfine interaction with the I Cu =3/2 nuclear spins of copper. They were assigned to Cu(II) ions in two lattice sites related by a 180° 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 g 1 =2.060(1), g 2 =2.068(2), g 3 =2.283(2), and A 1 ≈0.1×10 −4 , A 2 =13×10 −4 and A 3 =165×10 −4 cm −1 . The eigenvectors corresponding to g 3 and A 3 are coincident within the experimental error; the other eigenvectors are rotated 5.6° 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.