Construction of Metallosupramolecular Coordination Complexes: From Lanthanide Helicates to Octahedral Cages Showing Single-Molecule Magnet Behavior

Abstract

The construction of metallosupramolecular complexes toward interesting topological structures is a critical challenge for chemists. The fluctuation in the synthetic strategy, by keeping the same metal-ligand combination, has proved a very significant approach to construct metallosupramolecular architectures. Herein, by varying the reaction conditions four new Dy^III-supramolecular complexes based on a flexible dihydrazone ligand H₂L (H₂L = bis(2-hydroxy-3-methoxybenzylidene)adipohydrazide) in cooperation with different anions and solvents having formulas [Dy₄L₄(μ₂-N₃)₂](NO₃)₂·6CH₃OH·2H₂O (1), [Dy₈L₈(μ₂-CH₃OH)₄]Cl₈·6CH₃OH·14H₂O (2), [Dy₁₂L₁₂(μ₂-OH)₂(OH)₆(CH₃O)₂](NO₃)₂·2CH₃OH·14H₂O (3), and [Dy₁₂L₁₂(μ₂-OH)₂(NO₃)₂(OH)₃(CH₃O)](NO₃)₄·22H₂O (4), have been successfully synthesized and their crystal structures confirmed by single crystal X-ray diffraction studies. The structural study reveals that 1 and 2 have quadruple-stranded helicate and dual triple-stranded helicate supramolecular structures, respectively, while 3 and 4 display "octahedron" cagelike supramolecular structures. The magnetic studies reveal that complexes 1-3 exhibit slow magnetic relaxation behavior, while complex 4 displays a series of typical frequency-dependent relaxation signals at 0 Oe applied dc field which is a rare case in polynuclear 4f single-molecule magnet (SMM) family to date. Interestingly, the distinct magnetic dynamic behavior was noticed for nearly isoskeletal complexes 3 and 4, which can be attributed to the modification of the coordination environment around Dy^III ions.