Triclinic and orthorhombic polymorphs of 2-iodo-4-nitro­aniline: interplay of hydrogen bonds, nitro...I interactions and aromatic [pi]-[pi]-stacking interactions

In the triclinic polymorph of 2-iodo-4-nitro­aniline, C₆H₅IN₂O₂, space group P, the mol­ecules are linked by paired N-­H...O hydrogen bonds into C(8)[R(6)] chains of rings. These chains are linked into sheets by nitro...I interactions, and the sheets are pairwise linked by aromatic [pi]-[pi]-stacking interactions. In the orthorhombic polymorph, space group Pbca, the mol­ecules are linked by single N-H...O hydrogen bonds into spiral C(8) chains; the chains are linked by nitro...O interactions into sheets, each of which is linked to its two immediate neighbours by aromatic [pi]-[pi]-stacking inter­actions, so producing a continuous three-dimensional ­structure.

Hydro­gen-bonded chains in N-(2-nitrophenyl)phenylamine

Molecules of the title compound, C₁₂H₁₀N₂O₂, are markedly non-planar. There is an intramolecular N-H...O hydrogen bond, and the mol­ecules are linked into zigzag chains by a single C-H...O hydrogen bond. Comparisons are made with the supramolecular aggregation in isomeric amino-nitro derivatives, and in some N-methylnitro­anilines.

N,N′-Bis­[tris­(hydroxy­methyl)­methyl]­ethanedi­amide: six O—H...O hydrogen bonds generate only a two-­dimensional structure

Molecules of the title compound, C₁₀H₂₀N₂O₈, adopt a conformation which is almost centrosymmetric. The mol­ecules are disordered over two sets of sites with an occupancy ratio of 0.94:0.06. In the major form, there are two intramolecular O—H...O hydrogen bonds [O...O 2.756 (4) and 2.765 (4) Å; O—H...O 144 and 146°], in which the two amidic O atoms act as acceptors. In addition, there are four intermolecular O—H...O hydrogen bonds [O...O 2.650 (3)–2.666 (3) Å; O—H...O 158–171°]; these link each mol­ecule to six others in a continuous sheet structure which contains five distinct ring motifs, two of the S(7) type, two of the R(10) type and one of the R(22) type.