[Amino(iminio)methyl]phosphonate

The title compound, CH5N2O3P, exists as a zwitterion. The N atom of the imino group is protonated and the phosphonic acid group is deprotonated. The molecular geometry about the central C atom of this zwitterionic species was found to be strictly planar with the sum of the three angles about C being precisely 360°. In the crystal, the molecules are interlinked by O—H⋯O and N—H⋯O hydrogen-bonding interactions, forming a three-dimensional supramolecular network structure.

The title compound, CH 5 N 2 O 3 P, exists as a zwitterion. The N atom of the imino group is protonated and the phosphonic acid group is deprotonated. The molecular geometry about the central C atom of this zwitterionic species was found to be strictly planar with the sum of the three angles about C being precisely 360 . In the crystal, the molecules are interlinked by O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen-bonding interactions, forming a three-dimensional supramolecular network structure.

Comment
In the last decade considerable attention has been afforded to the synthesis of metal phosphonates due to their potential applications in ion-exchange and sorption, catalysis, magnetism and sensors (Ayyappan et al., 2001;Clearfield, 1998;Haga et al., 2007;Vivani et al., 2008;Bao et al., 2007;Cave et al., 2006;Cao et al., 1992;Ma et al., 2006Ma et al., , 2008. In order to synthseize metal phosphonates with novel structures and properties, many kinds of phosphonic acid ligands have been used. In order to study the crystal structure of phosphonic acid, we synthesized and determined the structure of the title compound ( Fig. 1). As shown in Scheme 1, the molecular exists as a zwitterion, the imino group being protonated and the phosphonic acid group being deprotonated. The molecular geometry about the central C atom is strictly planar with the sum of the three angles about C being precisely 360°. The three bonds about the central carbon atom consist of two nearly equivalent C-N1 and C-N2 distances of 1.299 (5) Å and 1.314 (5) Å, respectively, and a C-P bond distance of 1.845 (3) Å. These two C-N bonds are considerably shorter than a typical C-N single bond distance of 1.47 Å, Similar zwitterions have been formed by other aminoiminomethanesulfonic acids (Makarov et al.,1999). The P-O distances in these compounds range from 1.4872 (2) Å to 1.5872 (2) (Table 1). Thus the molecules are interlinked by these intermolecular hydrogen bonds, forming a three-dimensional supramolecular network structure (Fig.2).

Experimental
All solvents and chemicals were of analytical grade and were used without further purification. The title compound was prepared by the following reaction: A sample of 2,4,6-tri-(phosphonate ethyl)-1,3,5-triazine (9.8 g, 20 mmol) was dissolved in 6 mol/ ml HCl (20 ml), The mixture was heated (100 °C, 10 h) and then evaporated to dryness leaving a white solid.
Crystallization was carried out by dissolution of 0.62 g of the title compound (about 0.5 mmol) in 10 ml water, followed by evaporation at room temperature. After two weeks, colorless block crystals obtained.

Refinement
All non-hydrogen atoms were refined anisotropically, whereas the positions of all H atoms bonded to nitrogen were fixed geometrically (N-H = 0.86 Å), and included in the refinement in the riding mode, with Uĩso~(H) = 1.2U~eq~(N). The    (12)