Search

This paper reports two closely related heteropentanuclear manganese complexes, namely, {Na2Mn3(opch)3(μ4-O)(μ2-N3) (μ2-AcO)(μ2-MeO)}·6CH3OH·0.5H2O (1) and {Na2Mn3(opch)3(μ4-O)(μ2-N3)2(μ2-AcO)}·2.5CH3OH·2H2O (2), where H2opch is (E)-N′-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide. Single-crystal X-ray diffraction analysis reveals that the trigonal bipyramidal skeletons in both complexes are comparable, where a perfect triangular Mn3 motif occupies the equatorial plane. Magnetic investigations suggest that overall antiferromagnetic coupling is present within the triangles of 1 and 2. However, their dynamic magnetic properties are drastically distinct. Indeed, complexes 1 and 2 show two kinds of dual slow magnetic relaxation processes that correspond to anisotropy barriers (Δ) of 9.2 cm−1 (11.4 cm−1 for 2) and 12.8 cm−1 (30.0 cm−1 for 2) for the low- and high-frequency domains, respectively. More importantly, a further comparative study of the structure and magnetism indicates that the coordination sphere of these two model complexes with the homologous hydrazone-based coordination sites undergoes an alteration from methoxide-O to azide-N upon a subtle change of the auxiliary anion accompanied by modulating octahedron geometries, leading to a further influence on different relaxation dynamics.

{Dy16(μ6-C10H7PO3)2(μ5-C10H7PO3)8(spch)8(μ3-OH)2(μ2-OH)2(μ2-AcO)6(μ3-COO)2(DMF)2(H2O)6}·0.5CH3OH·4.5H2O (1) and {Dy16(μ5-C10H7PO3)4(μ3-C10H7PO3)12(μ2-C10H7PO3H)8(opch)4(DMF)8(MeOH)4}·2.5CH3OH·3H2O (2), where H2spch is ((E)-N'-(2-hydroxybenzylidene)pyrazine-2-carbohydrazide, C10H7PO3H2 is 1-naphthylphosphonic acid and H2opch is (E)-N'-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide, were successfully synthesized by varying the hydrazone ligands in the Dy-phosphonate system. It is important that the ellipsoidal core experiences a ring forming structural transformation to the supramolecular square motif upon the incorporation of an ortho-methoxy substituent into the hydrazone. Alternating-current (ac) magnetic susceptibility studies of 1 and 2 suggest that similar single molecule magnet behaviors occur for these two complexes. The result represents an effective molecular assembly tactic to develop highly complicated lanthanide coordination clusters through the multicomponent self-assembly of the coalescence of phosphonate- and hydrazone-based ligands and metal salts.