Nickel(II) complexes of tridentate anthracene based Schiff bases: syntheses, properties and crystal structures

The crystal and molecular structures of Ni(II) complexes with two tridentate anthracene-containing Schiff bases are reported. The Schiff bases were prepared by condensation of 9-anthraldehyde with diethylenetriamine (adien) and with dipropylenetriamine (adipn). Complexes synthesized from Ni(O2CCH3)(2) center dot 4H(2)O and the ligands (1 : 1 mol ratio) crystallize from methanol as [Ni(adien)(O2CCH3)(2)(H2O)] (1) and [Ni(adipn)(O2CCH3)(2)] center dot 2CH(3)OH (2 center dot 2CH(3)OH) in space groups P2(1)/n and P2(1)2(1)2(1), respectively. In 1, the distorted octahedral N3O3 coordination sphere around the metal ion is formed by the meridional N-3-donor adien, two mutually trans unidentate acetates and one water molecule. The N3O3 coordination sphere constituted by the N-3-donor adipn, one unidentate acetate and one bidentate acetate in 2 can be best described as trigonal bipyramidal. The secondary amine-N of adipn, the O-atom of the unidentate acetate and the midpoint of the two O-atoms of the bidentate acetate occupy the three equatorial positions and two imine-N atoms of adipn lie in axial sites. In the crystal lattice, molecules of 1 exist as discrete dimers due to intermolecular hydrogen bonding and pi-pi interactions. In contrast, self-assembly of 2 via intermolecular pi-pi interactions leads to a one-dimensional supramolecular structure.