6-Hydrazinylnicotinic acid: a powder study

The structure of the title compound, C6H7N3O2, is of interest with respect to radiopharmacueticals. The crystal packing is characterized by N—H⋯O and O—H⋯N hydrogen bonds, which form a three-dimensional network. The molecule is planar except for one of the amine H atoms.

The structure of the title compound, C 6 H 7 N 3 O 2 , is of interest with respect to radiopharmacueticals. The crystal packing is characterized by N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, which form a three-dimensional network. The molecule is planar except for one of the amine H atoms.

Related literature
For background on radiopharmacueticals, see: Callahan et al. (1996); Rennen et al. (2000). For general background, see: Abrams et al. (1990). For details of the synthesis, see: Schwartz et al. (1995). For geometric data, see: Allen et al. (1987). For descriptions of the powder diffraction profile, see: Thompson et al. (1987);Finger et al. (1994); Stephens (1999); Von Dreele (1997). For refinement by the LeBail method, see: Le Bail et al. (1988 Table 1 Hydrogen-bond geometry (Å , ). (ii) Àx þ 1; y þ 1 2 ; Àz þ 3 2 ; (iii) x þ 1; Ày þ 1 2 ; z þ 1 2 ; (iv) Àx; y À 1 2 ; Àz þ 3 2 .  Abrams et al., (1990), functions as a bifunctional chelating agent, forming a bridge between biomolecules and technetium (Callahan et al., 1996;Rennen et al., 2000). The (I) conjugated molecules react as monodentate ligands. Compound (I) is often used to synthesize bioconjugates for radiolabelling with 99m Tc and it is capable of efficient capture of technetium at extremely low concentrations. Compound (I) has a tendency to crystallize in the form of very fine pale yellow powder. Since no single-crystal of sufficient thickness and quality could be obtained, a structure determination by powder X-ray diffraction data was attempted. An ORTEP (Farrugia, 1997) view of compound (I) with atomic labeling is shown in Fig. 1. Bond lengths and angles in compound (I) are in their normal ranges (Allen et al., 1987). The crystal packing is characterized by intermolecular hydrogen bonds involving the hydroxyl H atom and the amine H atom (Table 1).The hydrogen bonds form a three dimensional network (Fig. 2).

Experimental
The synthesis of 6-hydrazinylnicotinic acid (I) was achieved according to the reported method (Schwartz et al., 1995). 6-Chloronicotinic acid (8.0 g) was added to 35 ml of 85% hydrazine hydrate. The reaction mixture was heated at 373 K for 4 h. The homogeneous reaction mixture was concentrated to dryness to give a white solid. This solid was dissolved in water and on acidification to pH 5.5 with concentrated hydrochloric acid a precipitate formed. The precipitate was filtered and the solid was washed with 95% ethanol and ether to give 4.52 g of a pale brown solid (I); yield 58%. 1 H and 13 C{1H} NMR spectra were recorded in DMSO-D6 on a Bruker Biospin 400 spectrometer. IR spectrum was recorded on a Jasco FT-IR 300E instrument. estimated to be equal to Z = 4, it can be concluded that the number of molecules in the asymmetric unit is Z′ = 1 for the space group P2 1 /c.
The structure was solved ab initio by direct methods using the program EXPO2009 (Altomare et al., 2009). The model found by this program was introduced in the program GSAS (Larson & Von Dreele, 2004) implemented in EXPGUI (Toby, 2001) for Rietveld refinements. During the Rietveld refinements, the effect of the asymmetry of low-order peaks was corrected using a pseudo-Voigt description of the peak shape (Thompson et al., 1987) which allows for angledependent asymmetry with axial divergence (Finger et al., 1994). The two asymmetry parameters of this function S/L and D/L were both fixed at 0.0225 during the Rietveld refinement. An excluded region from 85 to 95° (2θ) was used, which leads to better molecular geometry.
Non-H atoms were not restrained, but several restraints on bonds lengths and angles were applied to H atoms (see below). A planar group restraints to the aromatic ring and the carboxyl group, including their H atoms were also applied.
The H atoms of the NH, NH 2 , OH groups were located in a difference map. with isotropic displacement parameters (set to 1.2 times of the U eq of the parent atom for aromatic H atoms and to 1.5 times of the U eq of the parent atom for NH, NH 2 , OH groups).
Intensities were corrected from absorption effects with a µ.d value of 0.148. A spherical harmonics correction (Von Dreele, 1997) of intensities for preferred orientation was applied in the final refinement with 12 coefficients. The use of the preferred orientation correction leads to better molecular geometry with better agreement factors. The final Rietveld agreement factors are R p = 0.023, R wp = 0.030 R exp = 0.022, χ 2 = 1.904, and R F 2 = 0.02438. The final Rietveld plot of the X-ray diffraction pattern is given in Fig. 3.  The molecule structure of (I), showing the atom numbering. Displacement ellipsoids are drown at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

Figure 2
View of crystal packing of compound (I). Hydrogen bonds are shown as dashed lines.

Figure 3
Final Rietveld plot of compound (I). Observed data points are indicated by dots, the best-fit profile (upper trace) and the difference pattern (lower trace) are solid lines. The vertical bars indicate the positions of Bragg peaks.