Tetranuclear Cr-Ln ferrocenecarboxylate complexes with a defect-dicubane structure: synthesis, magnetism, and thermolysis

Using ferrocenecarboxylic acid (FcCO(2)H) and triethanolamine (H(3)tea) as ligands, the isostructural heterotrimetallic complexes [Ln(2)(III)Cr(2)(III)(OH)(2)(FcCO(2))(4)(NO3)(2)(Htea)(2)]center dot 2MePh center dot 2THF (Ln = Tb (1), Dy (2), Ho (3), Er (4), and Y (5); Fc = (eta(5)-C5H4)(eta(5)-C5H5)Fe; H(3)tea = N(CH2CH2OH)(3)) were obtained. In all of the complexes which possess a defective dicubane structure, two doubly deprotonated triethanolamine ligands chelate the chromium ions. However, during the synthesis of 1, an isomeric complex 1a in which Tb3+ is chelated by triethanolamine as a tetradentate ligand, was also isolated as a few single crystals. Magnetic susceptibility measurements revealed dominant antiferromagnetic interactions in the {Ln(2)(III)Cr(2)(III)} cores of 1-4 leading to the formation of complexes with an uncompensated magnetic moment, while weak Cr-Cr ferromagnetic interactions were detected in the Y analogue. Complexes 1, 2, and 3 exhibit single-molecule magnet properties dominated by an Orbach-type relaxation mechanism with magnetization reversal barriers (Delta/k(B)) estimated around 54, 75, and 47 K, respectively. The Dy complex exhibits a magnetization hysteresis in an applied magnetic field at temperatures below 4 K. Thermolysis of the complexes was studied by TGA and DSC techniques; the final products obtained under an air atmosphere contain mixed oxide Cr0.75Fe1.25O3 and heterotrimetallic oxide LnCr(1-x)Fe(x)O(3) (with x approximate to 0.75) phases.

Automated summary

By utilizing ferrocenecarboxylic acid and triethanolamine as ligands, a series of isostructural heterotrimetallic complexes were synthesized, exhibiting varying magnetic properties and single-molecule magnet behaviors among the terbium, dysprosium, holmium, erbium, and yttrium complexes.