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

摘要

Six Mn(III) quadridentate Schiff base compounds of 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(saltman)(H_2O)]ClO_4 (1), [Mn(naphtmen)(H_2O)]ClO_4 (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) A, 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)A for 3, 3,758(3) A for 4 and 3.505.(5)A 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 drmatically according to equatorial ligands, saltmen~(2-) or naphtmen~(2-), and axial ligands, H_2O, NCS~- and Cl~-. The relation between substitution of the ligands and strutural 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.