Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6IINiIII} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Abstract

Three polynuclear complexes, [NiNa(μ_1,1,1-N₃)(μ-hmb)₂(DMF)]₂, (1), [Ni₄(μ₃-OMe)₄(heb)₄(MeOH)_1.05(H₂O)_2.95], (2) and [Ni^III(OH)₆(hmb)₆Ni^II₆]·(ClO₄)₃ (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni₂Na₂N₂O₄}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni^III(OH)₆(hmb)₆Ni^II₆]³⁺ subunits and it represents the first nickel {Ni^II₆Ni^III} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1–3 in the 300–2 K have been discussed. The {Ni₂Na₂} (1) and {Ni₄} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ₃-N₃⁻ or μ₃-OCH₃⁻, while {Ni^II₆Ni^III} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ₃-OH⁻.