In Situ Ligand Transformation in the Synthesis of Manganese Complexes: Mono-, Tri- and a Barrel-shaped Tetradeca-nuclear Mn^II₁₄ 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[Mn^III₂Mn^II(μ-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^II₁₄(μ₆-CO₃)(μ₃-OH)₆(HLig-III)₆(HLig-IV)₃(OH₂)₃]·92MeCN (3), was isolated and characterized. Magnetic measurements on 2 indicate the presence of intramolecular and intermolecular antiferromagnetic interactions (J₁/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.