2-[3,5-Dioxo-4-(pyridin-3-yl)piperazin-1-yl]acetic acid

In the title compound, C11H11N3O4, the 3,5-dioxopiperazine ring adopts an envelope conformation, with the N atom connecting to the –CH2COOH group on the flap. In the crystal, molecules are linked by O—H⋯N hydrogen bonds to produce a linear chain running along the c axis. π–π stacking is observed between parallel pyridine rings of adjacent molecules, the centroid–centroid distance being 3.834 (2) Å.

In this molecule, the six membered piperazine-2,6-dionering has an envelope conformation with the N3 atom out of plane. The dihedral angle between the pyridine ring and the five-atom planar portion of the piperazine-2,6-dione ring is 77.9 (9)°. Also, the angle between mean plane containing acetic acid moiety and pyridine ring is 15.7 (8)°. As it is clear from figure 2, in the crystal packing of title molecule, the intermolecular O-H···N hydrogen bonds (Table 1) seem to be effective in the stabilization of the crystal structure.

Experimental
A solution of 3-aminopyridine (0.94 gr, 0.01 mole) in 20 ml pyridine was added to a solution of 1.91 gr (0.01 mole) nitrilotriacetic acid in 20 ml pyridine. The resulting solution was stirred at 313 K for 1 h, then 2.6 ml triphenyl phosphite was added dropwise, and the reaction mixture was stirred at 373 K for 10 h and at ambient temperature for 48 h. the product was obtained by addition of cold water to oyridine solution. X-ray quality crystals were obtained by slow diffusion of diethyl ether into a CH 2 Cl 2 solution at room temperature.

Refinement
The carboxyl H atom was located in a difference Fourier map and refined isotropically. Other H atoms were positioned geometrically with C-H = 0.93 and 0.97 Å for aromatic H and methylene H atoms, respectively, and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C).  The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Unit-cell packing diagram for (I). 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.6306 (