Magnetic properties of a europium(III) complex - possible multiplet crossover

A dinuclear complex [(H2O)Zn(LH)Eu(NO3)(3)] containing a hexadentate Schiff-base {N2O4}-donor ligand LH2- was prepared and characterized by X-ray structural analysis and IR, electronic and fluorescence spectroscopy. DC magnetic data show that upon heating the diamagnetic complex with the ground state Eu(III)-F-7(0) and Zn(II)-S-1 switches to paramagnetic species due to the population of F-7(J) (J = 1 to 6) magnetic multiplets. The magnetic susceptibility increases from zero, passes through a maximum, and then decreases upon heating. This behaviour can be explained using a spin-orbit Hamiltonian with an axial distortion term. There is an alternative interpretation of the susceptibility data based on a two-level model similar to that used in the spin crossover theory.