Towards a Series of Lanthanide-Bromides-Based Single Chain Magnets

In the field of molecular magnetism, experimentalists have focused their attention on Single Molecular Magnets (SMM) and Single Chains Magnets (SCM) because of their promising applications as memory devices. The efforts of synthesizing SMMs and SCMs have been mostly focused on high-spin molecules. In this endeavor, lanthanide-based molecules offer a rich field due to their capability of possessing a large number of unpaired electrons. However, molecules containing lanthanides in their 3+ oxidation state possess a weak interionic coupling and show poor magnetic properties. The highly contracted 4f orbitals preclude any appreciable f-f coupling between contiguous ions. In spite of the limitations of the lanthanide 3+ ions, magnetic coupling is greatly enhanced in reduced lanthanide clusters. The present research aims at the general exploratory synthesis of the lanthanide bromides beginning with the compounds adopting the Y₆I₁₀Ru-type structure. Experimental results show that reactions of LnBr₃ with metallic Ln turnings and metallic Z in Nb tubes at 850 – 900°C yield Ln₆Br₁₀Z (Ln = Gd, Tb, Ho and Z = Co, Ni). In this kind of cluster-linked chain compounds, Gd₆Br₁₀Co with 17e^- per cluster is expected to lead to ferromagnetic coupling; in contrast, Ni centered clusters, with 18e^- closed-shell configuration, is expected to show a weaker antiferromagnetic 4f-4f coupling. Phase identification is performed by X-ray powder diffraction and structural determination by single crystal X-ray. Theoretical studies are performed on Gd-based clusters using DFT and tight-binding calculations. Gadolinium-based compounds are the least complicated systems because Gd ions f⁷ configuration are without spin-orbit coupling effects.