Orthorhombic and monoclinic polymorphs of 1,3,5-triphenylperhydro-1,3,5-triazine-2,4,6-trione at 120 K: chains and sheets formed by C-H center dot center dot center dot pi(arene) hydrogen bonds

The title compound, C21H15N3O3, crystallizes in two polymorphic forms. In the orthorhombic polymorph, (I), in space group Fdd2 with Z' = 1, the molecules lie in general positions, while in the monoclinic polymorph, (II), in space group C2/c with Z' = 1 2, the molecules lie across twofold rotation axes. In each polymorph, the molecules are linked by a single C-H...pi(arene) hydrogen bond, forming chains in polymorph (I) and sheets in (II).