Out-of-plane dimers of Mn(III) quadridentate Schiff-base complexes with saltmen^2- and naphtmen^2- ligands: Structure analysis and ferromagnetic exchange

Six Mn(III) quadridentate Schiff base compounds with N,N′-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion (saltmen^2-) and N,N′-(1,1,2,2-tetramethylethylene)bis(naphthylideneiminato) dianion (naphtmen^2-) 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-O_phenolate 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-O_phenolate 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, saltmen^2- or naphtmen^2-, 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.