Gravar-mail: A tetra­nuclear cubane-like nickel(II) complex with a tridentate salicyl­idene­imine Schiff base ligand: tetra­kis­[μ(3)-4-methyl-N-(2-oxidophen­yl)salicylideneiminato]tetra­kis­[methano­lnickel(II)] methanol 0.8-solvate