Modulating the relaxation dynamics of the Na2Mn3 system via an auxiliary anion change.

Abstract

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.