2-(Aminocarbonyl)hydrazin-1-ium 6-carboxypicolinate

In the crystal structure of the title proton-transfer compound, CH6N3O+·C7H4NO4 −, O—H⋯O and N—H⋯O hydrogen bonds are formed respectively between the cations and the anions, each component affording a supramolecular chain along the c axis. The cation and anion chains are further linked by N—H⋯O and N—H⋯N hydrogen bonds. A π–π interaction is also observed between the pyridine rings; the interplanar separation and the centroid–centroid distance are 3.3425 (6) and 4.6256 (11) Å, respectively.


Comment
In the synthesis of crystal structure by design, the assembly of molecule unit in predefined arrangement is a key goal (Desiraju, 1997;Braga et al. 1998). The water soluble, proton transfer compounds can function as suitable ligands in the synthesis of metal complexes. In general, molecular association between carboxylic acid and a Lewis base results in more hydrogen bonding association with considerable stability upon a structure making process. This is because functionalized carboxylic acids and amines can enhance the intermolecular forces between the obtained cationic and anionic fragments, and these interactions can provide a large part of the stabilization energy of resulting self assembly systems (Moghimi et al., 2003(Moghimi et al., , 2007. Proton transfer from carboxylic acid to different amines has been reported (Moghimi et al. 2002;Aghabozorg et al., 2008;Soleimannejad et al., 2008). Herein, we report a novel PTC that have been synthesized using pyridine-2,6-dicarboxylic acid and hydrazinecarboxamide at room temperature and its crystal structure.
In the crystal structure of the compound, intermolecular hydrogen bonds link the molecules to form a proton transfer supramolecular framework. These hydrogen bonds help in the stabilization of the resulting supramolecular structure of the compound ( Table 1). The molecular structure of the title compound is shown in (Fig. 1). The crystal structure shows that a single proton from each of the carboxyl groups was transferred to the hydrazinecarboxamide. Thus, the negative charges of monoanionic pyridine-2,6-dicarboxylate groups, (pyH)-, are neutralized by a mono protonated hydraziniumcarboxamide fragment. The C-O distances for this compound support the existence of both ionic (COO) and non-ionic COOH group in the crystal structure of a new proton transfer system. The distance of ionic C-O in carboxylate ion is in the range of 1.250 Å due to resonance but in carboxylic acid group of pyridine-2,6-dicarboxylic acid has a deviation of 0.  (Fig. 2). The carboxylate group of one pyridine-2,6-dicarboxylic acid are bonded to OH of another pyridine-2,6-dicarboxylic acid through hydrogen bonding ( Fig. 3) with distance of 1.791 Å. In the packing diagram, crystal structure shows hydrogen bonding, ion pairing, π-π stacking and van der Waals interactions. The π-π stacking interactions exist between the two pyridine rings and between the pyridine ring and the NH 2 group of the cation with a centroid-centroid distance of 4.626 Å and a π-HN distance of 3.693 Å, respectively (Fig. 4). These interactions result in the formation of a supramolecular structure.

Experimental
Pyridine-2,6-dicarboxylic acid was purchased from Merck and used as received. Solvents dimethyl formamide (Loba-Chemie) and methanol (Qualigens) were used as received. Pyridine-2,6-dicarboxylic acid (11.69 g, 70 mmol) dissolved in methanol-water (100:175 ml) in hot condition over a period of 1 h 30 min. Semicarbazide hydrochloride (7.81 g, 70 mmol) dissolved in DMF-methanol (150:100 ml) was added to the pyridine-2,6-dicarboxylic acid solution in portions with continuous stirring. The reaction mixture was allowed to cool at RT with continuous stirring. The reaction mixture was supplementary materials sup-2 stirred for 48 h. However, no precipitation was seen. Subsequently, it was allowed to stand for 24 h. Transparent crystalline compound was seen at the bottom of the flask, which was separated by decanting the solution. Crystals were washed with methanol and dried in desiccator. The crystals are stable at room temperature.

Refinement
H atoms attached to atoms N3, N4 and O3 were refined freely. Other H atoms were introduced in calculated positions (C-H = 0.93 and N-H = 0.89 Å) and treated as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (N). Fig. 1. ORTEP diagram of the title compound, showing displacement ellipsoids at the 50% probability level for non-hydrogen atoms.     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 > σ(F 2 ) is used only for calculating Rfactors(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.

Figures
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )