Gravar-mail: 16-[(E)-4-Bromo­benzyl­idene]-13-(4-bromo­phen­yl)-2-hy­droxy-11-methyl-1,11-diaza­penta­cyclo­[12.3.1.0(2,10).0(3,8).0(10,14)]octa­deca-3(8),4,6-triene-9,15-dione