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 · nH2O and one [Ni2(HL2)L2]2(PF6)2 · 7H2O. 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 · 11H2O crystallized as [Ni(HL1)]4(PF6)4 · 0.5 CH3CH2OH · 2.8H2O 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.

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-benzoyl pyridine) carbohydrazone (H2L4). Three complexes were given a general formula of [Ni(HL)]4[PF6]4 · nH2O and one [Ni2(HL2)L2]2(PF6)2 · 7H2O. 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 · 11H2O crystallized as [Ni(HL1)]4(PF6)4 · 0.5 CH3CH2OH · 2.8H2O 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.Figure optionsDownload as PowerPoint slide