Insight into ferromagnetic interactions in Cu-Ln dimers with a compartmental ligand.

In the last two decades, efforts have been devoted to obtaining insight into the magnetic interactions between Cu and Ln utilizing experimental and theoretical means. Experimentally, it has been observed that the exchange coupling () in Cu-Ln systems is often found to be ferromagnetic for ≥4f metal ions. However, exchange interactions at sub-Kelvin temperatures between Cu and the anisotropic/isotropic Ln ions are not often explored. In this report, we have synthesized a series of heterobimetallic [CuLn(HL)(μ-piv)(piv)] complexes (Ln = Gd (1), Tb (2), Dy (3) and Er (4)) from a new compartmental Schiff base ligand, ,-bis(3-methoxy-5-methylsalicylidene)-1,3-diamino-2-propanol (HL). X-ray crystallographic analysis reveals that all four complexes are isostructural and isomorphous. Magnetic susceptibility measurements reveal a ferromagnetic coupling between the Cu ion and its respective Ln ion for all the complexes, as often observed. Moreover, μ-SQUID studies, at sub-Kelvin temperatures, show S-shaped hysteresis loops indicating the presence of antiferromagnetic coupling in complexes 1-3. The antiferromagnetic interaction is explained by considering the shortest Cu⋯Cu distance in the crystal structure. The nearly closed loops for 1-3 highlight their fast relaxation characteristics, while the opened loops for 4 might arise from intermolecular ordering. CASSCF calculations allow the quantitative assessment of the interactions, which are further supported by BS-DFT calculations.