Self-assembled macrocyclic molecular squares of Ni(II) derived from carbohydrazones and thiocarbohydrazones: Structural and magnetic studies

Four novel molecular square grids were achieved by self-assembly using the flexible ligands bis(di-2-pyridyl ketone) thiocarbohydrazone (H2L1), bis(quinoline-2-carbaldehyde) thiocarbohydrazone (H2L2), bis(di-2-pyridyl ketone) carbohydrazone (H2L3) and bis(2-benzoylpyridine) carbohydrazone (H2L4). Three complexes were given a general formula of [Ni(HL)](4)[PF6](4)center dot nH(2)O and one [Ni-2(HL2)L-2](2)(PF6)(2)center dot 7H(2)O. The MALDI-MS spectra reveal the formation of tetranuclear molecular squares. The square grid of the Ni(II) centers in all the complexes were organized by deprotonated ligands. The complex [Ni(HL1)(4)[PF6](4)center dot 11H(2)O crystallized as [Ni(HL1)](4)(PF6)(4)center dot 0.5CH(3)CH(2)OH center dot 2.8H(2)O and X-ray study revealed octahedral geometries around the Ni(II) centers. Variable temperature magnetic studies suggest intramolecular antiferromagnetic coupling between the Ni(II) electrons by a super exchange mechanism through intervening sulfur/oxygen atoms. (c) 2007 Elsevier Ltd. All rights reserved.