A re-examination of supra­molecular aggregation in two polymorphs of acetone 2,4-dinitro­phenyl­hydrazone

The structure of the triclinic polymorph of acetone 2,4-dinitrophenylhydrazone, C₉H₁₀N₄O₄, has been redetermined from diffraction data collected at 120 (2) K; the mol­ecules are linked by C-H...O hydrogen bonds into centrosymmetric R₂²(10) dimers which are themselves linked into a chain by an aromatic [pi]-[pi] stacking inter­action. In the monoclinic polymorph, which crystallizes with Z' = 2 in the space group P2₁/n, one type of mol­ecule forms dimers exactly as in the triclinic polymorph, while the other forms C(6) chains.