(R)-(1-Ammonioethyl)phosphonate

The title compound, C2H8NO3P, crystallizes in its zwitterionic form H3N+CH(CH3)PO(O−)(OH). In the crystal, the molecules are linked by N—H⋯O and O—H⋯O hydrogen bonds.

The title compound, C 2 H 8 NO 3 P, crystallizes in its zwitterionic form H 3 N + CH(CH 3 )PO(O À )(OH). In the crystal, the molecules are linked by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds.

Related literature
For the antibacterial activity of the title compound, see: Allen et al. (1979). For the use of the title compound as a co-crystallizing inhibitor on the X-ray structure of the alanine racemase from Bacillus anthracis, a potential anti-anthrax drug target, see: Au et al. (2008). For examples of coordination compounds of the title compound, see: Cui et al. (2006); Carraro et al. (2008). For a description of the graph-set notation for hydrogen-bonded aggregates, see: Grell et al. (1999). For previous work from our research group on the assembly of coordination polymers using phosphonic-based molecules, see: Cunha-Silva, Ananias et al.  Symmetry codes: (i) x þ 1; y; z; (ii) x þ 1 2 ; Ày þ 1 2 ; Àz; (iii) Àx; y þ 1 2 ; Àz þ 1 2 ; (iv) x À 1 2 ; Ày þ 1 2 ; Àz.

Comment
The title compound, R-1-aminoethylphosphonic acid (C 2 H 8 NO 3 P), is the phosphonic analogue of the amino acid alanine and, therefore, it is commonly represented as L-Ala-P (Au et al., 2008). It presents antibacterial activity (Allen et al., 1979) and it has been employed as inhibitor in the crystallization of the enzyme alanine racemase from Bacillus anthracis (Au et al., 2008). Remarkably, only two coordination compounds containing L-Ala-P as ligand are known, namely a racemic coordination polymer of zinc (Cui et al., 2006) and a chiral molybdenum cluster (Carraro et al., 2008).  Fig. 2], and the outer isolated O2-H4···O3 interactions (violet dashed bonds in Fig. 2). Supramolecular chains are in turn interconnected in the bc plane via the remnant N1 + -H2···O2 hydrogen bonds as depicted in Fig. 3 (orange dashed lines). It is noteworthy that all hydrogen bonding interactions are rather strong and directional: while the internuclear D···A distances range from 2.5484 (10) to 2.8369 (12) Å, the 〈(DHA) are all greater than 157°. As depicted in Fig. 3, the crystal packing promotes a close proximity between the substituent -CH 3 groups which point toward each other.

Experimental
The title compound was purchased from Sigma-Aldrich (>97.0%, Fluka) and was used as received without purification.
Suitable single crystals were grown from an aqueous solution over a period of two weeks.   Hydrogen atoms bound to carbon were located at their idealized positions and were included in the final model in the riding-motion approximation with C-H = 1.00 Å (tertiary C-H) or 0.98 Å (-CH 3 ). The isotropic thermal displacement parameters for these atoms were fixed at 1.2 (for methine-H) or 1.5 (methyl-H) times U eq of the respective parent atom.
Hydrogen atoms associated with the protonated -NH 3 + group or the pendant -OH moiety were located from difference Fourier maps and were included in the final model with the distances restrained to 0.95 (1) Å and U iso =1.5×U eq of the respective parent atom. The H···H distances of the -NH 3 + terminal group were further restrained to 1.55 (1) Å in order to ensure a chemically reasonable geometry for this moiety.   Table 1. Symmetry operations used to generate equivalent atoms have been omitted for simplicity.