Zwitterionic 6-methyl-2-oxo-3-[1-(ureidoiminio)ethyl]-2H-pyran-4-olate monohydrate

The title compound, C9H11N3O4·H2O, was prepared by the reaction of dehydroacetic acid and semicarbazide hydrochloride. It crystallizes in a zwitterionic form with cationic iminium and anionic enolate groups. In the crystal structure, the almost planar molecules are held together by N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, some of them involving the water molecules.

Data collection: COLLECT (Nonius, 1997); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 1999) and PARST (Nardelli, 1995). Comment NLO materials play an important role in the field of fibre optic communications and optical signal processing. In the last two decades, extensive research has shown that organic crystals can exhibit nonlinear optical efficiencies which are two orders of magnitude higher than those of inorganic materials. Semicarbazones of substituted benzaldehydes and acetophenones were reported to be some of the potential organic NLO materials.

Structure Reports Online
In this paper, the structure of the title compound (I), C 9 H 13 N 3 O 5 is reported. The asymmetric unit of (I) contains one Dehydroacetic acid semicarbazide molecule and one water molecule (Fig. 1).
The bond distances shown in Table 1 indicate that the C2-N3 iminium bond length of 1.303 (2) Å agree with similar bond in related compounds (Girija & Begum, 2004a;Girija et al., 2004b). This distance is slightly longer than a typical C=N bond (1.269 Å); but much shorter than the single carbon-nitrogen (1.409 Å) (Gowda et al. 2007), because of the resonance.  (Wojciechowski et al. 2003). The molecular configuration is determined by the presence of the intramolecular hydrogen bond O -···H-N + ( Table 2).
The main molecule in (I) is essentially planar, with a maximum deviation from the mean plane for the non-hydrogen atoms of 0.022 (2) Å. The iminium atom H3, participates in a strong intramolecular hydrogen bond with the enolate atom, O1 (Table 1), which generates an S(6) ring motif (Bernstein et al. 1995). Similar intramolecular hydrogen bonds were reported in the above-mentioned zwitterionic phenolates (Huang et al. 2006). This six-membered pseudocycle is almost planar, the maximum deviation from the mean plane being 0.012 Å for atom C2. The bond lengths and angles are in usual ranges (E)-1-(4-Hydroxybenzylidene) semicarbazide hemihydrate (Tai et al., 2007) and (E)-1-(4-Methoxybenzylidene) -semicarbazide .

Experimental
A mixture of dehydroacetic acid (0.01 mol) and semicarbazide hydrochloride (0.01 mol), in ethanol (20 ml) was refluxed for 1 h. After cooling, filtration and drying, the compound dehydroacetic acid semicarbazide was obtained. A small quantity supplementary materials sup-2 of this compound (10 mg) was dissolved in aqueous ethanol (95 / 12 ml), and the solution was then allowed to evaporate at room temperature. Prismatic yellow single crystals of the title compound were formed after 8 days.

Refinement
The O-H distances of the water molecules were restrained to 0.85 (1) Å, to ensure chemically reasonable geometry, with U iso fixed at 1.5Ueq(O). The iminium and ammino H atoms was located in a difference Fourier map and were refined isotropically. The methyl H atoms were constrained to an ideal geometry (C-H = 0.96 Å) with U iso (H) = 1.2U eq (C), but were allowed to rotate freely about the C-C bonds. H7 atom was placed in a geometrically idealized position (C-H = 0.93 Å) and constrained to ride on its parent atom with U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.   (7) 0.0036 (7) −0.0023 (7)  C2 0.0258 (9) 0.0274 (9) 0.0222 (8) 0.0011 (7) 0.0049 (7) 0.0004 (7)