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

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) Angstrom, 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 pi-pi 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.