Crystal structure of 1,3-bis[(E)-4-methoxybenzylideneamino]propan-2-ol

In the crystal of 1,3-bis[(E)-4-methoxybenzylideneamino]propan-2-ol, molecules are linked by O—H⋯N hydrogen bonds into C(5) supramolecular chains propagating along the a-axis direction.


Chemical context
Compounds containing the -C N-(azomethine group) structure are known as Schiff bases, usually synthesized from the condensation of primary amines and active carbonyl groups (Bekdemir & Efil, 2014). Imines are one class of the most important and fundamental unsaturated organic compounds with a C N double bond as their characteristic chemical bond and are extensively present in natural products and many drugs (Zhu et al., 2010). The formation of imines underlies a discipline known as dynamic covalent chemistry (DCC), which is now used widely in the construction of exotic molecules and extended structures such as rotaxanes, catenanes, and so on (Patil & Adimurthy, 2013). Schiff base compounds derived from 1,n-diamines play an important role in coordination chemistry and have been studied extensively for their broad range of biological activities (Sahu et al. 2012;da Silva et al., 2011;Przybylski et al. 2009;Dhar & Taploo, 1982). The common structural feature of these compounds is the presence of two azomethine groups linked by an n-methylene bridge, which can act as hydrogen-bond acceptors.
The title compound is interesting in that the presence of an OH group in the 1,3-diamine molecule is situated in a favorable position towards the azomethine groups to form an intramolecular hydrogen bond. Thus, one may expect that the charge distribution around the azomethine nitrogen atoms may be visibly perturbed by the presence of this type of interaction. Hence, 1,3-diaminepropan-2ol was chosen with the expectation that the presence of an OH group would result ISSN 2056-9890 in an intramolecular hydrogen bond. The title compound was synthesized quickly and efficiently by condensation of 1,3-diamine-2-propanol and p-methoxybenzaldehyde using a simple water-mediated procedure that requires neither a catalyst nor any additive (Rivera, et al., 2016). To the best of our knowledge, no X-ray crystal structure of either the uncoordinated or the coordinated title compound has been reported previously.

Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1. The title compound exists in an E,E conformation with respect to the N1 C1 and N2 C5 azomethine bonds and the C2-N1 C1-C11 and C4-N2 C5-C21 torsion angles are 175.6 (3) and À178.3 (3) respectively. The N1 C1 and N2 C5 distances of 1.265 (4) and 1.271 (4) Å , respectively, are consistent with C=N double bonding. The bond angles of 117.0 (3) and 117.7 (3) around the N1 and N2 atoms confirm their sp 2 character. The slight differences between N C distances and C-N C angles are due to the significant effect of the hydrogen bond on the geometric parameters of the nitrogen atom (N2) involved in the intermolecular hydrogen bond (see below).

Supramolecular features
Rather than the proposed intramolecular O-HÁ Á ÁN hydrogen bond, adjacent molecules in the crystal of the title compound are linked by intermolecular O-HÁ Á ÁN hydrogen bonds (Table 1, Fig. 2), forming an infinite zigzag C(5) chains extending along the a-axis direction. The chains are further linked to neighbouring chains through a pair of weak C-HÁ Á ÁO hydrogen bonds (Table 1). Furthermore, C12-H12 and C22-H22 form weaker C-HÁ Á ÁCg (-ring) interactions (Table 1), which connect the chains of consecutive layers, thus forming a three-dimensional supramolecular network ( The molecular structure of the title compound, Displacement ellipsoids are drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Partial packing diagram of the title compound, showing an extended hydrogen-bonded network. H atoms not involved in hydrogen bonds have been omitted for clarity.

Database survey
No comparable structure of either the uncoordinated or the coordinated title compound has been found in the Cambridge Crystallographic Database.

Synthesis and crystallization
The title compound was prepared according to our published method (Rivera et al., 2016). The crude product was dissolved in benzene and acetonitrile was added to the solution: upon slow evaporation of the solvent, colorless plates of the title compound arose. M.p. 403 K, yield 88%.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.