Different packing motifs mediated by hydrogen bonds in the hydro-chloride salts of two pyridoxal N-acyl-hydrazone derivatives.

The crystal structures of two hydro-chloride salts of pyridoxal-N-acyl-hydrazone-Q (Q = heterocyclic aromatic ring) derivatives, viz. (E)-3-hy-droxy-5-(hy-droxy-meth-yl)-2-methyl-4-{[(pyridin-4-ylformamido)-imino]-meth-yl}pyridin-1-ium chloride dihydrate, C14H15N4O3 +·Cl-·2H2O, (I), and (E)-3-hy-droxy-5-(hy-droxy-meth-yl)-2-methyl-4-{[(pyrimidin-2-ylformamido)-imino]-meth-yl}pyridin-1-ium chloride dihydrate, C13H14N5O3 +·Cl-·2H2O, (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 intra-molecular 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 hy-droxy-methyl 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 NHp (pyridine) grouping links to the terminal N atom of the pendant unprotonated pyridine ring of an adjacent cation to generate [010] chains, whereas the NHh (hydrazide) and OHhm (hy-droxy-meth-yl) moieties link to chloride ion acceptors. In (II), the NHp and OHhm groupings bond to chloride anions whereas NHh bonds to a water mol-ecule. Hydrogen-bonded chains of water mol-ecules occur in (I) and centrosymmetric tetra-mers in (II). The Hirshfeld surfaces of (I) and (II) are computed and the structures of related compounds are briefly compared.