Different packing motifs mediated by hydrogen bonds in the hydrochloride salts of two pyridoxal N-acylhydrazone derivatives

The crystal structures of two hydrochloride salts of pyridoxal– N -acylhydrazone–Q (Q = heterocyclic aromatic ring) derivatives, viz . ( E )-3-hydroxy-5-(hydroxymethyl)-2-methyl-4-{[(pyridin-4-ylformamido)imino]methyl}pyridin-1-ium chloride dihydrate, C 14 H 15 N 4 O 3 + ·Cl − ·2H 2 O, ( I ), and ( E )-3-hydroxy-5-(hydroxymethyl)-2-methyl-4-{[(pyrimidin-2-ylformamido)imino]methyl}pyridin-1-ium chloride dihydrate, C 13 H 14 N 5 O 3 + ·Cl − ·2H 2 O, ( II ) are described. The cations, which are protonated at the pyridine N atom of the pyridoxal ring, have similar overall conformations: the dihedral angles between the pyridoxal ring and the terminal aromatic ring are 12.63 (12) and 6.11 (15)° for ( I ) and ( II ), respectively. Each cation features an intramolecular O—H...N hydrogen bond, which closes an S (6) ring, but a difference arises in the conformation of the C—C—C—O fragment terminated by the the ring carbon atom bonded to the side chain and the O atom of the hydroxymethyl group: gauche for ( I ) and anti for ( II ). The extended structures of ( I ) and ( II ) feature numerous strong (N—H and O—H donors) and weak (C—H donor) hydrogen bonds. In ( I ), the NH p (pyridine) grouping links to the terminal N atom of the pendant unprotonated pyridine ring of an adjacent cation to generate [010] chains, whereas the NH h (hydrazide) and OH hm (hydroxymethyl) moieties link to chloride ion acceptors. In ( II ), the NH p and OH hm groupings bond to chloride anions whereas NH h bonds to a water molecule. Hydrogen-bonded chains of water molecules occur in ( I ) and centrosymmetric tetramers in ( II ). The Hirshfeld surfaces of ( I ) and ( II ) are computed and the structures of related compounds are briefly compared.