Insight into ferromagnetic interactions in Cu II –Ln III dimers with a compartmental ligand

In the last two decades, efforts have been devoted to obtaining insight into the magnetic interactions between Cu$^{II}$ and Ln$^{III}$ utilizing experimental and theoretical means. Experimentally, it has been observed that the exchange coupling (J) in Cu$^{II}$–Ln$^{III}$ systems is often found to be ferromagnetic for ≥4f$^7$ metal ions. However, exchange interactions at sub-Kelvin temperatures between Cu$^{II}$ and the anisotropic/isotropic Ln$^{III}$ ions are not often explored. In this report, we have synthesized a series of heterobimetallic [CuLn(HL)(μ-piv)(piv)$_2$] complexes (Ln$^{III}$ = Gd (1), Tb (2), Dy (3) and Er (4)) from a new compartmental Schiff base ligand, N,N’-bis(3-methoxy-5-methylsalicylidene)-1,3-diamino-2-propanol (H$_3$L). X-ray crystallographic analysis reveals that all four complexes are isostructural and isomorphous. Magnetic susceptibility measurements reveal a ferromagnetic coupling between the Cu$^{II}$ ion and its respective Ln$^{III}$ 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. ... mehrThe 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.