Heterometallic cubane-like {M2Ln2} ( M = Ni, Zn; Ln =, Gd, Dy) and {Ni2Y2} aggregates. Synthesis, structures and magnetic properties

The syntheses, structural determinations and magnetic studies of tetranuclear M(II)Ln(III) complexes (M = Ni, Zn; Ln = Y, Gd, Dy) involving an in situ compartmentalized schiff base ligand HL derived from the condensation of o-vanillin and 2-hydrazinopyridine as main ligand are described. Single-crystal X-ray diffraction reveals that all complexes are closely isostructural, with the central core composed of distorted {M(2)Ln(2)O(4)} cubes of the formulas [Ni(2)Ln(2)(mu(3)-OH)(2)(L)(2)(OAc)(4)(H2O)(3.5)](ClO4)(2)center dot 3H(2)O (Ln = Y 1 and Gd 2), [Ni2Dy2(mu(3)-OH)(2)(L)(2)(OAc)(5)(EtOH)(H2O)(1.5)](ClO4)center dot EtOH center dot H2O (3) and [Zn(2)Ln(2)(mu(3)-OH)(2)(L)(2)(OAc)(5)(EtOH)(H2O)](ClO4)center dot 2EtOH center dot 1.5H(2)O (Gd 4 and Dy 5). The Ln(III) ions are linked by two hydroxo bridges and each M-II ion is also involved in a double phenoxo-hydroxo bridge with the two Ln(III) ions, so that each hydroxo group is triply linked to the two Ln(III) and one M-II ions. The magnetic properties of all complexes have been investigated. Ni2Y2 (1) has a ferromagnetic Ni-II center dot center dot center dot Ni-II interaction. A weak ferromagnetic Ni-II center dot center dot center dot Ln(III) interaction is observed in the Ni(2)Ln(2) complexes (Ln = Gd 2, Dy 3), along with a weak antiferromagnetic Ln(III)center dot center dot center dot Ln(III) interaction, a D zero-field splitting term for the nickel ion and a ferromagnetic Ni-II center dot center dot center dot NiII interaction. The isomorphous Zn(2)Ln(2) (Ln = Gd 4, Dy 5) does confirm the presence of a weak antiferromagnetic Ln(III)center dot center dot center dot Ln(III) interaction. The Ni2Dy2 complex (3) does not behave as a SMM, which could result from a subtractive combination of the Dy and Ni anisotropies and an increased transverse anisotropy, leading to large tunnel splittings and quantum tunneling of magnetization. On the other hand, Zn2Dy2 (5) exhibits a possible SMM behavior, where its slow relaxation of magnetization is probably attributed to the presence of the anisotropic Dy-III ions.