(Z)-4-(2-Hydroxybenzylidene)-1-methyl-2-phenyl-1H-imidazol-5(4H)-one

In the title compound, C17H14N2O2, the asymmetric unit comprises two molecules that are comformationally similar [the dihedral angles between the phenyl rings in each are 46.35 (2) and 48.04 (3)°], with the conformation stabilized by intramolecular O—H⋯N hydrogen bonds, which generate S(7) rings. In the crystal, inversion-related molecules are linked by pairs of weak C—H⋯O hydrogen bonds, forming dimers with an R 2 2(16) graph-set motif. Weak inter-ring π–π stacking is observed in the structure, the shortest centroid-to-centroid distance being 3.7480 (13) Å.

In the title compound, C 17 H 14 N 2 O 2 , the asymmetric unit comprises two molecules that are comformationally similar [the dihedral angles between the phenyl rings in each are 46.35 (2) and 48.04 (3) ], with the conformation stabilized by intramolecular O-HÁ Á ÁN hydrogen bonds, which generate S(7) rings. In the crystal, inversion-related molecules are linked by pairs of weak C-HÁ Á ÁO hydrogen bonds, forming dimers with an R 2 2 (16) graph-set motif. Weak inter-ringstacking is observed in the structure, the shortest centroid-tocentroid distance being 3.7480 (13) Å .

Related literature
For the spectroscopy and preparation of the title compound, see: Chuang et al. (2011). For the applications of protontransfer dyes, see: Chen & Pang (2010) Tang et al. (2011). For a related structure, see: Chen et al. (2007). For graph-set theory of hydrogen bonds, see: Bernstein et al. (1995).

Comment
The excited-state intramolecular proton transfer (ESIPT) reaction of the title compound has been investigated recently (Chuang et al., 2011), which involves transfer of a hydroxy proton to the imine nitrogen through an intramolecular sevenmembered ring hydrogen-bonding system. The proton-transfer dyes have found many important applications.
The molecular structure of the title compound, C 17 H 14 N 2 O 2 is shown in Fig. 1. The asymmetric unit comprises two symmetry-independent molecules (A and B) which are comformationally similar [dihedral angles between the phenyl rings in each are 46.35 (2) and 48.04 (3)°]. The conformation stabilized in each by intramolecular O-H···N hydrogen bonds which generate S(7) rings (Chen et al., 2007). Present also are intramolecular C-H···O interactions between the methyl group and the ketone O-atom, generating S(5) rings (Table 1). In the crystal (Fig. 2), inversion-related molecules are linked by pairs of weak hydrogen bonds (Table 1), forming cyclic dimers with an R 2 2 (16) graph-set motif (Bernstein et al., 1995). Weak π-π stacking is also observed in the crystal structure, the shortest centroid-centroid distance being 3.7480 (13) Å [symmetry code: x, y -1, z].

Experimental
The title compound was synthesized according to the literature procedure (Chuang et al., 2011). Yellow needle-shaped crystals suitable for the crystallographic studies reported here were isolated over a period of six weeks by slow evaporation from a chloroform solution.

Refinement
The C-bound H atoms were positioned geometrically (C-H = 0.93-0.96 Å) and allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (C)]. The O-bound H atoms were positioned geometrically (O-H = 0.82 Å) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (O)].

Figure 2
A section of the crystal packing of the title compound, viewed along the b axis. Green and blue dashed lines denote the intermolecular C10-H10···O1 i and C30-H30···O3 ii hydrogen bonds, respectively. For symmetry codes (i) and (ii), see Table 1.

(Z)-4-(2-Hydroxybenzylidene)-1-methyl-2-phenyl-1H-imidazol-5(4H)-one
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.36 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.037 (2) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.   Symmetry codes: (i) −x+1, −y, −z; (ii) −x+1, −y+1, −z.