Vanishing exchange coupling between dissimilar copper ions in CuK 2(SO 4) 2·6H 2O as evidenced by X-band electron paramagnetic resonance

Abstract

We have studied the electron paramagnetic resonance (EPR) of a single crystal of the CuK 2(SO 4) 2·6H 2O Tutton salt when rotated around a and c ∗ axes, and around β(≡ b) and γ axes at X-band and room temperature. When the static magnetic field lies in the ( a, c) plane, both Cu 2+ ions are magnetically equivalent and EPR spectrum reduces to a singlet whose shape varies considerably, from a quasi-Lorentzian lineshape following the c axis, to an intermediate (between Gaussian and Lorentzian) lineshape following the a axis. For other orientations of the static magnetic field, the two Cu 2+ ions are magnetically unequivalent and the EPR spectrum is a moreorless resolved doublet. When the static magnetic field is parallel to a tetragonal axis, the EPR spectrum is a perfectly resolved doublet, revealing a very weak exchange interaction ( J′) between dissimilar ions. For the compound under study, the computer simulation of the EPR spectrum was carried out by adopting a convolution for the shape of the elementary line. This reveals that the exchange interaction between dissimilar ions is vanishingly small at room temperature at an accuracy of 0.0002 cm −1.