4-[(1-Benzyl-1H-1,2,3-triazol-4-yl)methoxy]benzene-1,2-dicarbonitrile: crystal structure, Hirshfeld surface analysis and energy-minimization calculations

The terminal rings in the title compound have an anti disposition in contrast to a syn conformation calculated in the energy-minimized structure. Supramolecular layers in the ab plane and sustained by methylene-C—H⋯N(triazolyl) and carbonitrile-N⋯π(benzene) interactions feature in the molecular packing.

In the solid state, the title compound, C 18 H 13 N 5 O, adopts a conformation whereby the phenyl ring and methoxy-benzene-1,2-dicarbonitrile residue (r.m.s. deviation of the 12 non-H atoms = 0.041 Å ) lie to opposite sides of the central triazolyl ring, forming dihedral angles of 79.30 (13) and 64.59 (10) , respectively; the dihedral angle between the outer rings is 14.88 (9) . This conformation is nearly 7 kcal mol À1 higher in energy than the energy-minimized structure which has a syn disposition of the outer rings, enabling intramolecularinteractions. In the crystal, methylene-C-HÁ Á ÁN(triazolyl) and carbonitrile-NÁ Á Á(benzene) interactions lead to supramolecular chains along the a axis. Supramolecular layers in the ab plane arise as the chains are connected by benzene-C-HÁ Á ÁN(carbonitrile) interactions; layers stack with no directional interactions between them. The specified intermolecular contacts along with other, weaker contributions to the supramolecular stabilization are analysed in a Hirshfeld surface analysis.

Chemical context
We have previously reported the crystal structure of bis[(phenylmethanamine-N)-(phthalocyaninato-4 N)zinc] phenylmethanamine trisolvate (Shamsudin et al., 2015) for use as a light-harvesting dye in dye-sensitized solar cells (DSSCs) (Kitamura et al., 2004, Nazeeruddin et al., 2001. Benzylamine was investigated as a solvent to assist coating TiO 2 nanoparticles with the highly insoluble zinc phthalocyanine. Another strategy for solubilizing phthalocyanine dyes is to append solubilizing groups to these large, aromatic structures (Mack et al., 2006). Phthalocyanines are somewhat unreactive and so this is most easily done by modifying the precursor phthalonitriles. Unsymmetrical phthalocyanines (e.g. tetrarather than octa-substituted) can yield constitutional isomers, but are more soluble (Eberhart & Hanack, 1997) and have a greater dipole moment which can make attractive molecules for non-linear optical applications (Tian et al., 1997). A particularly versatile and reliable reaction for the synthesis of analogues is the azide-alkyne Huisgen cycloaddition -the best known and most widely used reaction in the 'click chemistry' stable (Kolb et al., 2001). We therefore prepared 3-(prop-2-yn-1-yloxy)phthalonitrile by the S N Ar reaction of propagyl alcohol and 4-nitrophthalonitrile (Jan et al., 2013) and used this as a precursor for the synthesis of the title molecule (I), the structure of which is described herein along with a Hirshfeld surface analysis and the results of energy-minimization calculations.

Structural commentary
The central five-membered triazolyl ring in (I), Fig. 1, is strictly planar with the r.m.s. deviation for the five atoms being 0.003 Å . The phenyl ring of the N-bound benzyl group is almost perpendicular to this plane, forming a dihedral angle of 79.30 (13) . The 12 atoms comprising the methoxy-benzene-1,2-dicarbonitrile residue are almost co-planar with a r.m.s. deviation of 0.041 Å ; the maximum and minimum deviations are À0.085 (2) and 0.038 (2) Å for atoms C10 and C12, respectively. Within the triazolyl ring, the N2-N3 and C1-C2 bond lengths of 1.322 (3) and 1.367 (3) Å , respectively, are consistent with considerable double-bond character in each of these bonds, i.e. consistent with the electronic structure shown in the Scheme. The methoxy-benzene-1,2-dicarbonitrile residue lies to the opposite side of the central ring to the benzyl residue and forms a dihedral angle of 64.59 (10) with the triazolyl ring. The overall shape of the molecule is thus best described as a step with a dihedral angle between the outer rings of 14.62 (12) , consistent with these groups being approximately parallel.

Supramolecular features
The molecular packing in the crystal leads to supramolecular chains along the a axis, formed through the agency of methylene-C10-HÁ Á ÁN3(triazolyl) interactions involving both methylene-H atoms, which both link to N3 (Table 1). Encompassed within the chains are carbonitrile-N5Á Á Á(benzene) interactions, Table 1. The chains are connected into supramolecular layers in the ab plane by benzene-C12-HÁ Á ÁN4(carbonitrile) interactions across a centre of inversion so that ten-membered {Á Á ÁHC 3 N} 2 synthons are formed, Fig. 2 and Table 1. Layers inter-digitate along the c axis but do not form contacts within the standard distance criteria (Spek, 2009) The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the supramolecular layer in the ab plane in (I). The layer is sustained by C-HÁ Á ÁN and C-HÁ Á ÁN interactions shown as orange and purple dashed lines, respectively.

Hirshfeld surface analysis
The program Crystal Explorer 3.1 (Wolff et al., 2012) was used to generate Hirshfeld surfaces mapped over d norm , d e , curvedness and electrostatic potential. The electrostatic potential was calculated with TONTO (Spackman et al., 2008;Jayatilaka et al., 2005), integrated in Crystal Explorer, using the experimental geometry as the input. The electrostatic potentials were mapped on the Hirshfeld surface using the STO-3G basis set at the Hartree-Fock level of theory over a range AE0.075 au. The contact distances d i and d e from the Hirshfeld surface to the nearest atom inside and outside, respectively, enables the analysis of the intermolecular interactions through the mapping of d norm . The combination of d e and d i in the form of a two-dimensional fingerprint plot (Rohl et al., 2008) provides a summary of the intermolecular contacts in the crystal.
The intermolecular interactions of the C-HÁ Á ÁN type involving triazolyl-N3 and carbonitrile-N4 atoms as hydrogenbond acceptors, and the H10A, H10B and H12 hydrogen atoms as donors dominate the molecular packing. These interactions are easily recognized as bright-red spots, and are designated as 1, 2 and 3 in a square box, respectively, on the Hirshfeld surface mapped with d norm in Fig. 4. The surface mapped with electrostatic potential, Fig. 5, highlights these interactions as blue and red regions corresponding to positive (donor) and negative (acceptor) electrostatic potentials. The presence of such dominating interactions are also evident from the two dimensional fingerprint (FP) plots, Fig. 6; relative contributions to the overall surface are given in Table 2.
The prominent pair of sharp spikes of equal lengths (d e + d i $ 2.25 Å ) in the FP plot delineated into NÁ Á ÁH/HÁ Á ÁN contacts, Fig. 6d

Figure 4
Two views of the Hirshfeld surfaces for (I) mapped over d norm .

Figure 5
Hirshfeld surface for (I) mapped over the electrostatic potential.
the distinct pair of wings corresponding to CÁ Á ÁH/HÁ Á ÁC contacts, Fig. 6c, with a 25.8% contribution, combined, have a greater effect on the molecular packing than the dispersive HÁ Á ÁH contacts, Fig. 6b. The diminutive red spots on the surface mapped with d norm , designated as 4 in a square box of Fig. 4, at the phenyl-C9 and methylene-H3B atoms, reflect the presence of short intermolecular CÁ Á ÁH contacts [C9Á Á ÁH3B i = 2.79 Å for symmetry code: (i) À1 + x, y, z]. The short intramolecular HÁ Á ÁH contact between the benzene-H16 and Omethylene-H10A atoms (H10AÁ Á ÁH16 = 2.09 Å ) can be recognized from two neighbouring blue regions on the surface mapped with electrostatic potential in Fig. 5. The presence of a comparatively weak C-NÁ Á Á interaction can be viewed from the negative potential around the carbonitrile-N5 atom (red region) and the light-blue region around the phenyl ring in Fig. 5; the strength of this interaction is quantified as 3.7 and 3.5% relative contribution from CÁ Á ÁC and CÁ Á ÁN contacts to the surface. The small flat segments delineated by a blue outline in the surface mapped with curvedness, Fig. 7, and the small contribution from CÁ Á ÁC contacts, i.e. 3.5%, to the surface is consistent with the absence of significantstacking interactions in the structure.

Database survey
There are four closely related structures to (I) in the crystallographic literature (Groom & Allen, 2014). The chemical structures of (II)-(V) are shown in Scheme 2, salient dihedral angles are given in Table 3 and a comparison between molecules is shown in Fig. 8. The similarity in the structures is seen in the relationship between the central triazolyl ring and pendent phenyl rings. By contrast to the conformation observed in (I), which was described above as anti with respect to the relative orientation of the N-and C-bound residues to the central ring, a syn disposition is observed in each of (II) (Rostovtsev et al., 2002), (III) (Garcia et al., 2011)

Figure 6
The two-dimensional fingerprint plots for (  Hirshfeld surface for (I) mapped over curvedness.

Energy-minimization calculations
The structure of (I) was subjected to energy-minimization calculations with Density-Functional Theory (DFT) using the LC-wPBE functional (Vydrov & Scuseria, 2006;Vydrov et al., 2006), as implemented in the Gaussian program (Frisch et al., 2009), and the exchange-hole dipole moment (XDM) dispersion correction (Becke & Johnson, 2007;Otero-de-la-Roza & Johnson, 2013) with the 6-31+G* basis set. Fig. 9 shows an energy profile as the 1,2-dicarbonitrile residue is rotated (30 steps) about the O-C bond with respect to the rest of the molecule. The energy profile shown in Fig. 9 reveals the observed anti conformation of (I) is in fact a high-energy conformation, being nearly 7 kcal mol À1 higher in energy than the low-energy conformation which, as shown in Fig. 10, has a syn conformation of the aromatic rings. In the energy-mini-mized structure, the dihedral angles between the fivemembered ring and the dinitrile-and benzyl-benzene rings are 73.6 and 85.2 , respectively, i.e. differing by ca 9 and 6 , respectively, from the comparable angles in the experimental  Energy profile (kcal mol À1 ) for conformations of (I) differing by a rotation (30 steps) about the O-C bond.

Figure 10
Overlay diagram of the experimental (red image) and energy-minimized (blue) structures of (I). The molecules have been overlapped so that the five-membered rings are coincident.
structure. The dihedral angles between the aromatic rings is 23.4 . While the dihedral angles do not differ significantly between the experimental and gas-phase, energy-minimized structures, the relative conformations are quite distinct. The syn orientation of the terminal rings is most likely stabilized by intramolecularinteractions, the shortest intramolecular CÁ Á ÁC contact between rings being 3.62 Å . The adoption of a different conformation in the experimental structure no doubt relates to the dictates of global crystal packing considerations.

Synthesis and crystallization
3-(Prop-2-yn-1-yloxy)phthalonitrile (Jan et al., 2013; 0.10 g, 0.55 mmol), CuSO 4 (0.032 g), sodium ascorbate (0.13 g) and benzyl azide (0.074 g) were dissolved in 75% aqueous acetone (20 ml) and stirred for 48 h at room temperature. The reaction was poured into ice-water and the resulting off-white solid was collected by vacuum filtration and was recrystallized as light-brown prisms from a solvent mixture of dichloromethane and hexane (

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 4. Carbon-bound H atoms were placed in calculated positions (C-H = 0.95-0.99 Å ) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U eq (C).   PRO (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), QMol (Gans & Shalloway, 2001) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010). 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.