In Situ Ligand Transformation in the Synthesis of Manganese Complexes: Mono-, Tri- and a Barrel-shaped Tetradeca-nuclear Mn14II Aggregate

Three one-pot syntheses leading to four examples of in situ ligand transformations are presented. These in situ reactions involve various transformations of 2 -(N'-dicyanomethylene-hydrazino)-benzoic acid (DHB). The resulting ligands enabled the preparation of three new coordination compounds, which were fully, characterized by infrared spectroscopy, elemental analysis, and single crystal X-ray diffraction. The complex, [Mn-III(Lig-I)(CH3OH)Cl] (1), was prepared in a one-pot synthesis in which the aryl hydrazone ligand, (Lig-I)(2-), was formed by the amination of DHB resulting from the nucleophilic attack of an amino group of ethylenediamine. The linear, mixed-valence trinuclear complex, (Et3NH)(4)[(Mn2MnII)-Mn-III(mu-OH)(2)(Lig-II)(2)(HLig-II)(2)] (2), was synthesized using a preparation involving the in situ reaction of azide and a nitrile of DHB. Larger species can also be prepared using this technique. In a reaction involving two different in situ ligand formations, the cyclocondensation of two DHB molecules and the partial hydrolysis of a nitrile of DHB, the first example of a tetradecanuclear Mn(II) aggregate, (H3O)(4)[Mn-14(II)(mu(6)-CO3)(mu(3)-OH)(6)(HLig-III)(6)(HLig-IV)(3)(OH2)(3)]center dot 92MeCN (3), was isolated and characterized. Magnetic measurements on 2 indicate the presence of intramolecular and intermolecular antiferromagnetic interactions (J(1)/k(B) = -9.5(1) K, g = 1.95(2), and zJ'/k(B) = -0.37(5) K) while those on 3 suggest the presence of dominating antiferromagnetic interactions.