Dichlorido{(E)-4-dimethylamino-N′-[(pyridin-2-yl)methylidene-κN]benzohydrazide-κO}zinc

In the mononuclear title complex, [ZnCl2(C15H16N4O)], the ZnII cation is five-coordinated in a strongly distorted square-pyramidal environment by two Cl− anions and a neutral tridentate Schiff base ligand. The ZnII cation is chelated by the carbonyl O atom, the imine N atom and the pyridine N atom, which causes a slight loss of planarity for the ligand; the dihedral angle between the aromatic rings is 4.61 (8)°.

In the mononuclear title complex, [ZnCl 2 (C 15 H 16 N 4 O)], the Zn II cation is five-coordinated in a strongly distorted squarepyramidal environment by two Cl À anions and a neutral tridentate Schiff base ligand. The Zn II cation is chelated by the carbonyl O atom, the imine N atom and the pyridine N atom, which causes a slight loss of planarity for the ligand; the dihedral angle between the aromatic rings is 4.61 (8) .  Ma et al. (2011). For the structure of the ligand and its complex with CuCl 2 , see: ; Sangeetha, Pal, Anson et al. (2000). For the design of molecular dynamic systems, see: Hirose (2010); Lehn (2006). For the synthetic principles of compounds exhibiting dynamic properties, see Kay et al. (2007). For information storage, see: Kandel (2001).
The author is grateful to the Service de radiocristallographie de l'Institut de Chimie (Strasbourg) and to the Universidad del Valle in Cali, Colombia, for partial financial support.

Comment
Similar to bis-pyridyl hydrazones derivatives, pyridine-2-carboxaldehyde acyl (aroyl) hydrazones are able to undergo configurational (E/Z) isomerization and constitutional changes as well as their structure allows them to coordinate to metallic centers by a tridentade NNO binding site (Chaur et al., 2011). Therefore, the C=N bond of these hydrazones can be used in double dynamic processes of interest for information storage (Lehn, 2006;Kay et al., 2007). The configurational dynamics of these compounds give access to short term photoactivated metastable states. On the other hand, they can undergo constitutional dynamics by constituent exchange allowing long term storage of information (Kandel, 2001).
Thus the pyridyl-acyl hydrazones are appealing compounds for the design of systems exhibiting multiple states and interconversion processes that involve configurational/constitutional changes, as well as metal coordination (Ma et al., 2011). These features together with increasing time scales being of interest for the development of both short-term and long-term molecular information storage and processing devices that may be addressed by orthogonal transformations involving either physical stimuli (light, heat; see Hirose, 2010) or chemical effectors (amino components or metal cations).
In this regard our group focuses on the design of bis-pyridyl and pyridyl-acyl hydrazones, as the title compound ( Fig.   1), for the implementation of dynamic systems exhibiting reversible multiplex states for information storage (Moreno-Fuquen et al., 2012). The new complex is based on a ligand for which the structure has been previously established , as well as a Cu(II) complex (Sangeetha, Pal, Anson et al., 2000).
The title complex exhibits a distorted five-coordinated square-pyramidal disposition (Fig. 2). The Schiff base ligand is not planar (Fig. 3), resulting in a dihedral angle between the planes of the aromatic and pyridyl rings of 4.61 (8)°, while the free ligand is planar . The molecules stack forming columns along the [001] direction by intermolecular hydrogen bonds with a distance N3-H3···Cl2 = 3.199 (2) Å. Also it is observed a weak π-π slipped stacking interaction between the aromatic rings, with separations between ring centroids of 3.8075 (1) Å (Fig. 4).
The reaction mixture was refluxed for three hours, then the precipitate was collected in a Büchner funnel and recrystallized from ethanol affording the ligand in a 90% yield. DMSO solution of the zinc complex.

Refinement
All H atoms were placed in idealized positions, with C-H bond lengths fixed to 0.93 (aromatic CH) or 0.96 Å (methyl), and refined as riding with displacement parameters calculated as U iso (H) = xU eq (carrier C) where x = 1.2 (aromatic CH) or 1.5 (methyl).

Figure 1
The synthetic route for the title complex.

Figure 2
The structure of the title compound with displacement ellipsoids drawn at the 50% probability level.   Stacking of the molecules forming a column along the [001] direction.