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

Three polynuclear complexes, [NiNa(mu(1,1,1)-N-3)(mu-hmb)(2)(DMF)](2), (1), [Ni-4 mu(3)-OMe)(4)(heb)(4)-(MeOH)(1.05)(H2O)(2.95)], (2) and [N-iIII(OH)(6)(hmb)(6)Ni-6(II)]center dot(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)(6)Ni (II)(6)](3+) subunits and it represents the first nickel {Ni-6(II) Ni-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 {Ni-4} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through mu(3)-N-3(-) -or mu(3)-OCH3-, while {Ni-II (6NiI)-I-II} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through mu(3)-OH-.