Gravar-mail: Di-μ(2)-acetato-di-μ(2)-azido-di-μ(3)-methanol-tetra­kis­{μ-2-[(2-methyl-1-oxidopropan-2-yl)imino­meth­yl]-6-meth­oxy­phenolato}tetra­nickel(II) methanol disolvate