Ab initio study of the antiferromagnetic coupling in the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25– anion

Abstract

The most stable spin configuration in the Cu₂₀ unit embedded in the P₈W₄₈O₁₈₄ POM framework has been analyzed with ab initio computational methods. Because of the large size of the Cu₂₀ unit, a fragment approach has been adopted to compute the four possible magnetic interactions. Difference Dedicated Configuration Interaction results reveal that the magnetic coupling between unpaired copper electrons ranges from ferromagnetic (J = 14.8 cm⁻¹) to antiferromagnetic (J = −72.6 cm⁻¹). With the four calculated J-values we have performed a simulation of the magnetic susceptibility vs. temperature by using the Ising model and a Monte Carlo algorithm to sample the spin configurations. The most stable spin alignment, governed by the most intense antiferromagnetic interaction, features 12 up and 8 down spins. There is no full cancellation of spins that can comply with the magnetic interactions found for this molecule.