Crystal structure of 3-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacen-3-yl)propanoic acid

The crystal structure of the title compound has been determined at 100 K. In the crystal, O—H⋯O, C—H⋯On and C—H⋯F hydrogen bonds, and C—H⋯π and π–π interactions connect neighbouring molecules.


Chemical context
Boron-dipyrromethene (BODIPY) dyes have promising applications in material sciences for labeling biomolecules such as peptides, proteins, lipids and nucleic acids. BODIPY dyes have many advantages over other dyes, such as robustness against light and chemicals, high absorption coefficients and fluorescence quantum yields, narrow emission bandwidths, and so on (Boens et al., 2012). Moreover, their spectroscopic and photophysical properties are easy to tune by attachment of some residues at the appropriate positions of the difluoroboron dipyrromethene moiety (Loudet & Burgess, 2007;Ulrich et al., 2008). Herein we report the crystal structure of the title compound ( Fig. 1) having the BODIPY fragment.

Structural commentary
The title compound is composed of a boron-dipyrromethene (BODIPY) backbone and a propionic acid group. The BODIPY fused-ring system is nearly planar, with a maximum deviation from the mean plane of 0.032 (2) Å for atom N4.

Figure 1
The molecular structure of the title compound, showing the atomnumbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

Synthesis and crystallization
The title compound was synthesized according to a previously described method (Giessler et al., 2010;Bihovsky & Pendrak, 1996). The compound was purified by column chromatography. Single crystals were obtained by slow evaporation from a mixed solution of cyclohexane/dichloromethane (1:1 vv) at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atom of the carboxyl group was refined freely, while the other H atoms were placed in geometrically idealized positions (C-H = 0.93-0.97 Å ) and treated as riding on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for methylene and aromatic H atoms.   SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics:

Funding information
PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.20 e Å −3 Δρ min = −0.19 e Å −3 sup-2 . E73, 1974-1976 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.