Cooperative effect of multiple hydrogen bonding involving the nitro group: solid state dimeric self-assembly of o-, m- and p-hydroxyphenyl-2,4-dinitrophenylhydrazones

Abstract

Solid state studies of o-, m-, and p-hydroxyphenyl-2,4-dinitrophenylhydrazones: 1, 2, 3 and 4 (3·0.5 MeCN) revealed dimeric self-assembly of molecules. A pattern of two NH⋯O₂N and up to six CH⋯O₂N intermolecular hydrogen bonds creates cohesive forces between two molecules of the dimer. Push–pull effects of numerous weak interactions generate non-bonding contacts between negatively charged O atoms of the o-NO₂ groups in the range 2.683(2)–2.894(3) Å, far below the sum of van der Waals radii. Both the presence of OH groups and MeCN molecules in the crystals does not interfere much with dimer formation. Low temperature X-ray data collected for compound 1 provided evidence that due to the involvement of the o-NO₂ group oxygen in a new type of intramolecular, resonance-assisted hydrogen-bonded system (RAHB), the phenyl ring has a 2,5-diene geometry. The packing patterns observed in crystals of compounds 1–4 are explained as a result of competition between in-plane hydrogen bonding and inter-planar interactions dominated by π–π stacking and dipole–dipole overlap. FT-IR data confirm aggregation in solution. Another examples of short contacts between nitro group oxygens found in the Cambridge Crystallographic Database are discussed.