Gravar-mail: Bis{μ(2)-2-[(2-hy­droxy­eth­yl)(meth­yl)amino]­ethano­lato}bis­(μ(3)-N-methyl-2,2′-aza­nediyldiethano­lato)tetra­kis­(thio­cyan­atato-κN)dichromium(III)dimanganese(II) dimethyl­formamide tetra­solvate