Syntheses, structures, and magnetic properties of three new MnII–[MoIII(CN)7]4− molecular magnets

Abstract

By reaction of K₄[Mo^III(CN)₇]·2H₂O, Mn(ClO₄)₂·6H₂O and bidentate chelating ligands, three new cyano-bridged compounds, namely Mn₂(3-pypz)(H₂O)(CH₃CN)[Mo(CN)₇] (1), Mn₂(1-pypz)(H₂O)(CH₃CN)[Mo(CN)₇] (2) and Mn₂(pyim)(H₂O)(CH₃CN)[Mo(CN)₇] (3) (3-pypz = 2-(1H-pyrazol-3-yl)pyridine, 1-pypz = 2-(1H-pyrazol-1-yl)pyridine, pyim = 2-(1H-imidazol-2-yl)pyridine), have been synthesized and characterized structurally and magnetically. Single crystal X-ray analyses revealed that although the chelating ligands are different, compounds 1 to 3 are isomorphous and crystallize in the same monoclinic space group C2/m. Connected by the bridging cyano groups, one crystallographically unique [Mo(CN)₇]⁴⁻ unit and three crystallographically unique Mn^II ions of different coordination environments form similar three-dimensional frameworks, which have a four-nodal 3,4,4,7-connecting topological net with a vertex symbol of {4³}{4⁴·6²}₂{4¹⁰·6¹¹}. Magnetic measurements revealed that compounds 1–3 display long-range magnetic ordering with critical temperatures of 64, 66 and 62 K, respectively. These compounds are rare examples of a small number of chelating co-ligand coordinated [Mo(CN)₇]⁴⁻-based magnetic materials. Specifically, the bidentate chelating ligands were successfully introduced into the heptacyanomolybdate system for the first time.