• 𝑆 ̂𝑗 (1) where the first term corresponds to the single ion axial anisotropy of the Re IV ion, the second term is the Zeeman effect of the applied magnetic field, and the third term the exchange interaction between the constituent (Cu II , Re IV ) metal centres. The χT product and the variable temperature variable field magnetisation data for 1-3 were simultaneously fitted to spin-Hamiltonian ( ), affording the best fit parameters collected in Table . 1). See the main text and Table for the best-fit parameters.