Crystal structure of difluorido{2-[(4-hydroxyphenyl)diazenyl]-3,5-dimethylpyrrolido}boron

The asymmetric unit contains two independent molecules, which are linked by an O—H⋯O hydrogen bond. The dimers are further assembled into one-dimensional ladder like structure through O—H⋯F hydrogen bonds and stabilized by π–π interactions. The ladders are further linked by C—H⋯π contacts.

The Hirshfeld surfaces of the two conformers were generated using CrystalExplorer (Turner et al., 2017). Fig. 3 clearly shows that the two conformers are involved in different supramolecular interactions.

Synthesis and crystallization
To a solution of 2-(4-hydroxylphenylazo)-3,5-dimethyl-1-Hpyrrole (2 mmol, 0.43g) and triethylamine (6 mL) in dry dichloromethane (15 mL) was slowly added boron trifluoride ethyl ether (2 mL). The resulting solution was stirred for 40 min, and then saturated potassium carbonate solution was added and stirred for 30 minutes. The resulting solution was extracted with ethyl acetate (10 mL Â 3) and evaporated under vacuum to dryness. The residue was purified by column chromatography, eluting with ethyl acetate and petroleum Hirshfeld surfaces of the two conformers mapped over d norm in the range À0.614 to 1.350 a.u. The intermolecular contacts can be seen in red regions. Table 2 Hydrogen-bond geometry (Å , ).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. OH H atoms were located from difference-Fourier maps and refined freely. Other H atoms were placed in calculated positions (C-H = 0.93 or 0.96 Å ) and refined using a riding model, with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl).

Funding information
Funding for this research was provided by: National Natural Science Foundation of China (No. 21172174).  (Rigaku OD, 2015); cell refinement: CrysAlis PRO (Rigaku OD, 2015); data reduction: CrysAlis PRO (Rigaku OD, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq F1