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.