Crystal structure and DFT study of (E)-4-[({4-[(pyridin-2-ylmethylidene)amino]phenyl}amino)methyl]phenol

The title Schiff base compound is considerably non-planar, with the outer phenol and pyridine rings being inclined to each other by 70.21 (3)°.


Chemical context
Schiff bases often exhibit various biological activities and, in many cases, have been shown to have antibacterial, anticancer, anti-inflammatory and antitoxic properties (Lozier et al., 1975). Hydroxy Schiff bases have been studied extensively for their biological, photochromic and thermochromic properties (Garnovskii et al., 1993;Hadjoudis et al., 2004). They can be used as potential materials for optical memory and switch devices (Zhao et al., 2007). Schiff bases derived from pyridinecarbaldehydes have also attracted considerable interest in synthetic chemistry. This category covers a diverse range of bidentate or polydentate bridging (Wu & Liang, 2008;Dong et al., 2000;Knö dler et al., 2000), which played a significant role in coordination chemistry (Faizi & Hussain, 2014). Transition metal complexes of pyridyl Schiff bases have found applications in laser dyes (Genady et al., 2008), catalysis (Wang et al., 2008) and in crystal engineering, as they form coordination polymers (Huh & Lee, 2007) or grid-type complexes (Nitschke et al., 2004). The present work is part of an ongoing structural study of Schiff bases (Faizi et al., 2016) and their utilization in the synthesis of metal complexes (Faizi & Prisyazhnaya, 2015). We report herein on the crystal structure and DFT computational calculation of the title Schiff base compound.

Figure 2
A view along the b axis of the inversion dimers, formed via. pairs of O-HÁ Á ÁN hydrogen bonds (thin blue lines), enclosing an R 2 2 (32) ring motif. The dimers are linked by N-HÁ Á ÁO hydrogen bonds (see Table 1 for details).

Figure 3
A view along the a axis of the layer-like structure in the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (Table 1) and only the H atoms involved in hydrogen bonding have been included.

Figure 1
A view of the molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 40% probability level. gave a number of hits for the principal moiety of the title compound, i.e. N-(2-pyridylmethylene)benzene-1,4-diamine (CSD refcode EXOQAK; Marjani et al., 2011), and its metal complexes. The pyridine ring in EXOQAK is inclined to the benzene ring by 24.69 (13) and the adjacent amine and pyridine N atoms are trans to each another. In the title compound, the pyridine ring is inclined to the benzene ring by 15.13 (14) and the N atoms are also trans to each another. This is in contrast to the situation in the metal complexes of EXOQAK, e.g. dichloro{N-[(pyridin-2-yl)methylene]benzene-1,4-diamine}zinc(II) (CSD refcode TUJXIG; Marjani et al., 2009), where on coordination, the pyridine ring rotates and the adjacent amine and pyridine N atoms are then cis to each other.

DFT study
The DFT quantum-chemical calculations were performed at the B3LYP/6-311 G(d,p) level (Becke, 1993) as implemented in GAUSSIAN09 (Frisch et al., 2009). DFT structure optimization of (I) was performed starting from the X-ray geometry and the values compared with experimental values (see Table 2). In general, the calculated values are in good agreement with the experimental data.
The highest occupied molecular orbitals (HOMO) and lowest unoccupied orbitals (LUMO) are named frontier orbitals (FMOs). The LUMO and HOMO orbital energy parameters are considerably answerable for the charge transfer, chemical reactivity and kinetic/thermodynamic stability of a molecule 1. The DFT study of the title compound revealed that the HOMO and LUMO are localized in the plane extending from the whole phenol ring to the pyridine ring and electron distribution of the HOMO-1, HOMO, LUMO and the LUMO+1 energy levels are shown in Fig. 4. Molecular orbitals of HOMO contain both and character, whereas HOMO-1 is dominated by -orbital density. The LUMO is mainly composed of -density, while LUMO+1 is composed of both and electron density. The HOMO-LUMO energy gap is very important for the chemical activity and explains the eventual charge transfer interaction within the molecule. The HOMO-LUMO gap was found to be 0.128907 a.u. and the frontier molecular orbital energies, E HOMO and E LUMO were found to be as À0.19367 and À0.06476 a.u., respectively.

Synthesis and crystallization
The title compound was prepared from an equimolar mixture of 4-aminophenylaminomethylphenol (0.50 g, 2.3 mmol) and pyridine-2-carbaldehyde (0.20 g, 2.30 mmol) in (50 ml) methanol. The yellow reaction mixture was stirred for 3 h at room temperature and solvent was evaporated to 5 ml. The resulting yellow solid was isolated by filtration, washed successively with a cold water and methanol mixture (10 ml) and hexane (20 ml). The compound was recrystallized from hot methanol, giving yellow plate-like crystals. Finally, the yellow solid was dried in a vacuum desiccator (yield 0.50 g, 70%; m.p. 446-448 K). Spectroscopic

Refinement
Crystal data, data collection and structure refinement details are summarized in Electron distribution of the HOMO-1, HOMO, LUMO and LUMO+1 energy levels for the title molecule.   Data collection: SMART (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.14 e Å −3 Δρ min = −0.15 e Å −3 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.