Out-of-plane dimers of Mn(iii) quadridentate Schiff-base complexes with saltmen2– and naphtmen2– ligands: structure analysis and ferromagnetic exchange

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Abstract
Six Mn(III) quadridentate Schiff base compounds with N,N′-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion (saltmen2−) and N,N′-(1,1,2,2-tetramethylethylene)bis(naphthylideneiminato) dianion (naphtmen2−) have been prepared and structurally characterized: [Mn(saltmen)(H2O)]ClO4 (1), [Mn(naphtmen)(H2O)]ClO4 (2), [Mn(saltmen)(NCS)] (3), [Mn(naphtmen)(NCS)] (4), [Mn(saltmen)(Cl)] (5) and [Mn(naphtmen)(Cl)] (6). Among them, 1 and 2 form phenolate-bridged out-of-plane dimers with Mn–Ophenolate bond distances of 2.434(2) and 2.662(3) Å, respectively. X-Ray diffraction analysis shows that compounds 3, 4 and 6 can also be considered as out-of-plane dimers in spite of long Mn–Ophenolate interacting distances (3.441(2) Å for 3, 3.758(3) Å for 4 and 3.505(5) Å for 6). In contrast with the above compounds, 5 is a discrete Mn(III) mononuclear complex with a square-pyramidal geometry. In the dimer series (compounds 1–4 and 6), the out-of-plane intermolecular distance varies dramatically according to equatorial ligands, saltmen2− or naphtmen2−, and axial ligands, H2O, NCS− and Cl−. The relation between substitution of the ligands and structural parameters of the dimeric molecules are discussed. Magnetic susceptibility studies reveal interesting intra-dimer ferromagnetic interactions between Mn(III) ions. Our work reports on these new S = 4 building blocks that open new possibilities in the design of magnetic molecule-based materials.

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