Ferromagnetically coupled tetranuclear Ni(ii)-2-oxy-aceto- or benzo-phenonate complexes.

Reaction of 2-hydroxy-acetophenone (HL) or 2-hydroxy-benzophenone (HL') with nickel(ii) acetate provides the tetrakis-[(μ3-methanolato-κ3 O:O:O)(methanol-κO)(2-oxyacetophenone-κ2 O,O')nickel(ii)], [Ni(L)(μ3-CH3O)(CH3OH)]4 (1) or tetrakis-[(μ3-methanolato-κ3 O:O:O)(aqua-κO)(2-oxybenzophenone-κ2 O,O')nickel(ii)] monohydrate, [Ni(L')(μ3-CH3O)(H2O)]4·H2O (2). Molecular structure determination demonstrates each nickel(ii) ion is six-coordinate with a distorted octahedral geometry defined by three oxygen atoms from three methoxide fragments, a methanol (1) or water (2) molecule, and two oxygen atoms from the acetophenonate (L-) or benzophenonate (L'-) ligand, such that the four nickel atoms and four methoxide groups represent a cubane-type structural topology with each methoxide fragment bridging three of the metal centers. Stabilization of the cubane core occurs via intramolecular O-H⋯O hydrogen bonds. Solid-state magnetic measurements along with computational modeling confirm dominant ferromagnetic interactions for the compounds, attributed to their cubane topology and the Ni-O-Ni angles adopting values lower than 100°. Thermogravimetric analysis (TGA) suggests thermal decomposition of the complexes with successive release of the lattice water, coordinated solvents (MeOH or H2O), OCH3 groups and fragmented ligand species, supported by differential scanning calorimetry (DSC) studies. Cyclic voltammetry reveals a quasi-reversible two electrons charge transfer process in N,N-dimethylformamide.