Two tetranuclear 3d–4f complexes: Syntheses, structures and magnetic properties

Heterometallic 3d-4f Complexes as Air-Stable Molecular Precursors in Low Temperature Syntheses of Stoichiometric Rare-Earth Orthoferrite Powders

Four 3d-4f hetero-polymetallic complexes [Fe₂Ln₂((OCH₂)₃CR)₂(O₂C^tBu)₆(H₂O)₄] (where Ln = La (1 and 2) and Gd (3 and 4); and R = Me (1 and 3) and Et (2 and 4)) are synthesized and analyzed using elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and SQUID magnetometry. Crystal structures are obtained for both methyl derivatives and show that the complexes are isostructural and adopt a defective dicubane topology. The four heavy metals are connected with two alkoxide bridges. These four precursors are used as single-source precursors to prepare rare-earth orthoferrite pervoskites of the form LnFeO₃. Thermal decomposition in a ceramic boat in a tube furnace gives orthorhombic LnFeO₃ powders using optimized temperatures and decomposition times: LaFeO₃ formed at 650 °C over 30 min, whereas GdFeO₃ formed at 750 °C over 18 h. These materials are structurally characterized using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray map spectroscopy, and SQUID magnetometry. EDX spectroscopy mapping reveals a homogeneous spatial distribution of elements for all four materials consistent with LnFeO₃. Magnetic measurements on complexes 1-4 confirm the presence of weak antiferromagnetic coupling between the central Fe(III) ions of the clusters and negligible ferromagnetic interaction with peripheral Gd(III) ions in 3 and 4. Zero-field-cooled and field-cooled measurements of magnetization of LaFeO₃ and GdFeO₃ in the solid-state suggest that both materials are ferromagnetic, and both materials show open magnetic hysteresis loops at 5 and 300 K, with M_sat higher than previously reported for these nanomaterials. We conclude that this is a new and facile low temperature route to these important magnetic materials that is potentially universal, limited only by what metals can be programmed into the precursor complexes.

Three 3d–4f Tetranuclear Complexes Based on 2,3,5-Trichlorobenzoic Acid: Syntheses, Structures, and Magnetic Properties

The solvothermal reactions of 2,3,5-trichlorobenzoic acid (HL) 2,2′-bipyridine (bipy), CoCl2·6H2O, and Ln2O3 afforded three novel 3d–4f tetranuclear complexes Co2Ln2(L)10(bipy)2 (Ln = Dy 1, Ho 2, and Er 3), which have been characterized by single-crystal X-ray diffraction, infrared spectroscopy, and element analyses. Complexes 1–3 crystallize in the triclinic space group P1, and the completely deprotonated L ligands possess μ2 : η2, η1 and μ2 : η1, η1 coordination modes to bridge adjacent metal ions, which further connect into 2D layers by hydrogen bonds. Magnetic studies indicate ferromagnetic interactions between adjacent metal ions in complexes 1 and 3.