Crystal structure of fluroxypyr

The title compound {systematic name: 2-[(4-amino-3,5-dichloro-6-fluoropyridin-2-yl)oxy]acetic acid}, C7H5Cl2FN2O3, is a pyridine herbicide. In the crystal, N—H⋯O, O—H⋯O and N—H⋯F hydrogen bonds and weak π–π interactions connect chains of molecules into a three-dimensional network.


Chemical context
Fluroxypyr belongs to the pyridine family of herbicides. It is widely used on cereal crops, olive trees and fallow croplands to control broad-leaf weeds (Moreno-Castilla et al., 2012;Wang et al., 2011). Pyridine herbicides such as fluroxypyr are effective and popular chemicals for post-emergence broad-leaf weed control, particularly in turf during cool seasons. The efficacy of this herbicide may be affected by environmental conditions including the relative humidity, temperature and soil moisture. Because of this, its application often provides inconsistent broad-leaf weed control in winter or early spring (Reed & McCullough, 2012). Until now, its crystal structure had not been reported and we describe it herein.

Structural commentary
The structure of fluroxypyr is shown in Fig. 1. The dihedral angle between the mean plane of the carboxylic acid group (C6/C7/O2/O3) and the pyridyl ring (N1/C1-C5) is 77.5 (1) . All bond lengths and bond angles are normal and comparable to those observed in the crystal structure of a related pyridinecontaining herbicide (Cho et al., 2015). ISSN 2056-9890

Figure 2
A view along the b axis of the crystal packing of the title compound. The chains are formed through intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds (yellow dashed lines). H atoms not involved in these interactions have been omitted for clarity.

Figure 3
The two-dimensional network formed through intermolecular N-HÁ Á ÁF hydrogen bonds (red dashed lines). Intermolecular O/N-HÁ Á ÁO hydrogen bonds within a chain are shown as yellow dashed lines. H atoms not involved in these interactions have been omitted for clarity.

Figure 1
The structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radius.

Synthesis and crystallization
The title compound was purchased from Dr. Ehrenstorfer GmbH. Colorless single crystals suitable for X-ray diffraction were obtained from a CH 3 CN solution by slow evaporation at room temperature.

2-[(4-Amino-3,5-dichloro-6-fluoropyridin-2-yl)oxy]acetic acid
Crystal data 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 )