Anisotropic exchange in linear chain complexes of copper(II)

An improved formula for the second moment of the electron paramagnetic resonance line is found for the case of both anisotropic exchange (a.e.) and magnetic dipole interactions between localized spins. The width Γ of the exchange-narrowed EPR line is then obtained by using the Blume–Hubbard result for spin dynamics and by preferentially weighting the secular a.e. and dipolar terms in one-dimensional systems. The angular and temperature dependence of Γ for copper(II) pyrazine nitrate are reported. The linewidth is adequately described in this linear chain system once the a.e. interaction and the one-dimensional linewidth correction are included. The EPR data confirm the postulated direction for strong exchange and provide a convenient method for evaluating the a.e. term. Previously reported single crystal EPR linewidths data for two other linear chain complexes, copper(II) benzoate trihydrate and copper(II) pyridine chloride, are also analyzed in terms of a.e. along the chain. In all three crystals, a.e. is comparable to the magnetic dipole–dipole interaction.