A ferromagnetically coupled single hydroxido bridged tetranuclear nickel(II) Schiff base complex incorporating a Ni₄O₄ cubane core: crystal structure and magnetic study

The new tetranuclear nickel(II) complex [Ni-4(OH)(L)(HL)(2)(CH3OH)(1.5)(H2O)(1.5)]center dot 9H(2)O (1) has been synthesised by the reaction of NiCl2 center dot 6H(2)O and the Schiff base ligand H3L (H3L = (CH3O)(OH)C6H3CH=N-C(CH3) (CH2OH)(2)), prepared by the 1:1 condensation of 2-amino-2-methyl-1,3-propanediol and o-vanillin, and characterized by different physicochemical methods. Single crystal X-ray structural determination identifies a Ni4O4 cubane moiety as the central part of the complex unit. The presence of a single mu(3)-hydroxido bridged oxygen occupying only one vertex of the Ni4O4 cubane core is rare in Ni4O4 cubanes (ca. 5% of occurrence). Structural analysis also reveals two similar alkoxido oxygen atoms of the Schiff base coordinating the metals in two different modes; one in the mu(3)-bridging mode whilst the other binds in a monodentate fashion. The metal centers display distorted octahedral geometries with two different coordination environments. The magnetic properties reveal the presence of ferromagnetic nickel(II)-nickel(II) interactions in the cluster with two different exchange pathways. The magnetic data can be fitted to a Ni4O4 cubane model with g = 2.058, J(1) = +17.2 cm(-1) and J(2) = +6.6 cm(-1). Isothermal magnetization measurements confirm the S = 4 spin ground state. Both J values agree with previous magneto-structural correlations in doubly oxido-bridged nickel(II) complexes. (C) 2013 Elsevier Ltd. All rights reserved.