Crystal structures of two 4H-chromene derivatives: 2-amino-3-cyano-4-(3,4-dichlorophenyl)-7-hydroxy-4H-benzo[1,2-b]pyran 1,4-dioxane monosolvate and 2-amino-3-cyano-4-(2,6-dichlorophenyl)-7-hydroxy-4H-benzo[1,2-b]pyran

In the structures of two title compounds, the 4H-chromene derivative molecules are linked by N—H⋯O and N—H⋯N hydrogen bonds, forming double layers or ribbons.


Structural commentary
The asymmetric units of the title compounds are illustrated in Figs. 1 and 2. The molecules of the two 4H-chromene derivatives differ only in the positions of the chlorine atoms attached to the phenyl ring, and the key bond dimensions in (I) and (II) essentially coincide. The bicyclic chromene cores in the two structures are nearly planar, with the largest deviation from the mean plane being observed for the sp 3 -hybridized C7 atom in both cases [0.081 (2) and 0.087 (2) Å in (I) and (II), respectively]. The interatomic distances in the pyran rings indicate a strong -conjugation of the electron-donating atoms O2 and N2 with the cyano acceptor groups. As a result of this conjugation, the C8 C9 bonds [1.349 (3) Å in (I) and 1.354 (2) Å in (II)] are longer than the typical double bonds (Allen et al., 1987), whereas the C9-N2 bonds are shortened [1.335 (3) and 1.342 (2) Å for (I) and (II), respectively], thus the amino groups in the studied structures were assumed to be planar and treated with the AFIX 43 instruction. Besides this, the O-C distances in the pyran rings are asymmetric [1.393 (2) and 1.393 (2) Å for O2-C10 vs. 1.357 (3) and 1.353 (2) Å for O2-C9 in (I) and (II), respectively]. The observed planarity of the bicyclic chromene units is also a consequence of -conjugation. The dihedral angle between the mean planes of the 4H-chromene ring system and the phenyl ring attached to C7 is 80.82 (9) in (I) and 85.36 (8) in (II). In (II), the o-chlorine atom Cl1 forms short intramolecular contacts with atoms C8 and C9 of the pyran ring of 3.111 (2) and 3.193 (2) Å , respectively.

Figure 1
The asymmetric unit of (I), with atom labelling and 50% probability displacement ellipsoids. The hydrogen bond is represented by a dashed line.  (Table 2) also contribute to the stability of crystal structure.

Synthesis and crystallization
Both studied compounds were prepared by the same procedure. Mixtures of 3,4-chlorobenzaldehyde (8.75 g, 0.05 mol) [for (I)] or 2,4-dichlorobenzaldehyde (8.75 g, 0.05 mol) [for (II)], malononitrile (3.3 ml, 0.05 mol) and resorcinol (5.5 g, 0.05 mol) in 150 ml of water were refluxed for about 10-20 minutes in 250 ml round-bottom flasks. The progress of the reaction was monitored by thin layer chromatography using silica gel-G plates. After the product had formed, the reaction mixtures were kept in the refrigerator overnight. The solid mass that settled was filtered using a suction pump, washed well with a mixture of methanol and water and dried in air. The crude products were recrystallized from methanol giving white powders. Single crystals were grown by slow evaporation of solutions in 1,4-dioxane (I) or acetonitrile (II). The melting points are 518-523 K for (I) and 513-515 K for (II).

Refinement
Crystal data, diffraction data and structure refinement details for (I) and (II) are summarized in Table 3. All hydrogen atoms bound to C and N were located from the difference-Fourier maps and refined isotropically using a riding model, with U iso (H) = 1.2U eq (C,N) and C-H = 0.98 Å for methine, 0.97 Å for methylene and 0.93 Å for aromatic C atoms, and N-H = 0.86 Å . In (I), the hydroxy H atom was constrained with AFIX 147, but its U iso value was allowed to refine freely. In (II), the OH hydrogen atom was freely refined. Double layers of hydrogen-bonded molecules in (I). The 1,4-dioxane molecules are omitted for clarity.

Figure 4
A view of the hydrogen-bonding interactions in (II), showing the formation of centrosymmetric dimers and ribbons. The C-bound hydrogen atoms are omitted for clarity. [Symmetry codes:  program(s) used to refine structure: SHELXL2014/6 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2007) and Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON (Spek, 2009).

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. 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 > 2sigma(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.

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.