Crystal structure, DFT and MEP study of (E)-2-{[(3-chlorophenyl)imino]methyl}-6-methylphenol

In the crystal structure of the title compound, molecules are linked through C—H⋯O hydrogen bonds and C—H⋯π interactions, forming chains parallel to the [010] direction. The molecular geometry in the ground state was been calculated using DFT. Additionally, frontier molecular orbital and molecular electrostatic potential map analyses were performed.


Chemical context
Schiff bases, known as anils, imines or azomethines, have recently received considerable attention because of their good performance in coordination chemistry and anti-bacterial, anti-cancer and herbicidal applications (Piotr et al., 2009;Schiff, 1864). The presence of a lone pair of electrons in an sp 2hybridized orbital on the nitrogen atom of the azomethine group is of considerable chemical and biological importance (Sinha et al., 2008). In a continuation of our interest in the chemical, herbicidal and biological properties of Schiff bases we synthesized the title compound, (I), as a potential antibacterial agent (Yılmaz et al., 2012).
We report herein the synthesis, crystal structure and quantum chemical computational studies of the Schiff base compound, (I).

Structural commentary
The structure of the title compound (I) is shown in Fig. 1. It crystallizes in the orthorhombic space group Pbca with eight molecules in the unit cell. The molecular structure has two planar rings. The whole molecule is approximately planar, with a maximum deviation of À0.0236 (12) Å from planarity for the C8 atom of Schiff base. The title compound displays an E configuration with respect to the C8 N double bond. The dihedral angle between the two phenyl ring planes is 0.34 (9) and the C5-C8-N1-C9 torsion angle is À179.81 (15) . The planar molecular conformation is stabilized by the intramolecular O1-H1Á Á ÁN1 hydrogen bond, which forms an S(6) motif.

Figure 1
A view of the molecular structure of (I) with the atom labelling. The dotted line indicates the intramolecular O-HÁ Á ÁN hydrogen bond. Displacement ellipsoids are shown at the 40% probability level. ties of a molecular system (Koepnick et al., 2010;Solomon et al., 2012;Jafari et al., 2013). A molecule with a small frontier orbital gap is more polarizable than one with a large gap and is considered a soft molecule because of its high chemical reactivity and low kinetic stability (Prabavathi et al., 2015). The energy levels of the HOMO (highest occupied molecular orbital), HOMO-1, LUMO (lowest occupied molecular orbital) and LUMO+1 orbitals calculated at the B3LYP/6-311++G(2d,2p) level (Frisch et al., 2009;Dennington et al., 2007) for (I) are shown in Fig. 4. The HOMO, HOMO-1 and LUMO orbitals are delocalized over the two phenyl rings connected by a Schiff base bridge and HOMO and HOMO-1 can be said to be -bonding orbitals. The LUMO+1 orbitals are delocalized on the chlorophenyl ring and the C atom of the Schiff base. LUMO and LUMO+1 orbitals exhibit * antibonding character. The energy gap of (I) is 4.069 eV. The other molecular orbital energies are shown in Fig. 4. Electron affinity (A) and ionization potential (IP) can be defined as A = ÀE LUMO and IP = ÀE HOMO . Additionally, these values can also be used calculate the electronegativity (), chemical hardness () and chemical softness (S) (Prabavathi et al., 2015;Karunakaran & Balachandran, 2014). For the title compound (I), A = 2.201 eV, IP = 6.270 eV, = 4.236 eV, = 2.035 eV, and S = 0.246 eV.

Molecular electrostatic potential surface analysis
The analysis of a three-dimensional plot of the molecular electrostatic potential (MEP) surface is a technique for mapping the electrostatic potential onto the isoelectronic density surface, providing information about the reactive sites. The surface simultaneously displays molecular size and shape and the electrostatic potential value. In the colour scheme adopted, red indicates an electron-rich region with a partial negative charge and blue an electron-deficient region with partial positive charge, light blue indicates a slightly electrondeficient region, yellow a slightly electron-rich region and green a neutral region (Politzer et al., 2002). The MEP map of (I) was obtained by the B3LYP/6-311++G(2d,2p) method. In Fig. 5, it is shown that (I) has two possible sites of electrophilic attack. The negative region is localized on the protonated oxygen atom of methylphenol ring, O1, with a minimum value of À0.031 a.u. Positive potential sites of the compound are around hydrogen atoms. However, the maximum positive region is localized on the hydrogen atom bonded to the C atom forming the Schiff base, which can be considered as one possible site for nucleophilic attack, with a maximum value of 0.027 a.u. Molecular electrostatic potential (MEP) map calculated at the B3LYP/6-311++G(2d,2p) level.

Figure 4
Plots of the frontier orbitals and the energy gap for (I).
crystals suitable for X-ray measurements were obtained by recrystallization from methanol at room temperature.

(E)-2-{[(3-Chlorophenyl)imino]methyl}-6-methylphenol
Crystal data 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.