2,4‐Di­nitro­phenyl­hydrazones of 2,4‐di­hydroxy­benz­aldehyde, 2,4‐di­hydroxy­aceto­phenone and 2,4‐di­hydroxy­benzo­phenone

In 2,4‐di­hydroxy­benz­aldehyde 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­amide solvate {or 4‐(2,4‐di­nitro­phenyl)­hydrazono­methyl]­benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate}, C₁₃H₁₀N₄O₆·C₃H₇NO, (X), 2,4‐di­hydroxy­aceto­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­am­ide solvate (or 4‐{1‐(2,4‐di­nitro­phenyl)hydrazono]ethyl}benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate), C₁₄H₁₂N₄O₆·C₃H₇NO, (XI), and 2,4‐di­hydroxy­benzo­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­acet­amide solvate (or 4‐­{(2,4‐di­nitro­phenyl)hydrazono]phenyl­methyl}benzene‐1,3‐diol N,N‐di­methyl­acet­amide solvate), C₁₉H₁₄N₄O₆·C₄H₉NO, (XII), the molecules all lack a center of symmetry, crystallize in centrosymmetric space groups and have been observed to exhibit non‐linear optical activity. In each case, the hydrazone skeleton is fairly planar, facilitated by the presence of two intramolecular hydrogen bonds and some partial N—N double‐bond character. Each molecule is hydrogen bonded to one solvent mol­ecule.