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], C(13)H(10)N(4)O(6).C(3)H(7)NO, (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), C(14)H(12)N(4)O(6).C(3)H(7)NO, (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), C(19)H(14)N(4)O(6).C(4)H(9)NO, (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.