(R)-(1-Ammoniopropyl)phosphonate

The title compound, C3H10NO3P, crystallizes in its zwitterionic form, H3N+CH(C2H5)PO(O−)(OH), with the asymmetric unit being composed by two of such entities (Z′ = 2). The crystal packing leads to a sequence of hydrophobic and hydrophilic layers. While the hydrophobic layer comprises the aliphatic substituent groups, the hydrophilic one is held together by a series of strong and rather directional N+—H⋯O and O—H⋯O hydrogen bonds.

The title compound, C 3 H 10 NO 3 P, crystallizes in its zwitterionic form, H 3 N + CH(C 2 H 5 )PO(O À )(OH), with the asymmetric unit being composed by two of such entities (Z 0 = 2). The crystal packing leads to a sequence of hydrophobic and hydrophilic layers. While the hydrophobic layer comprises the aliphatic substituent groups, the hydrophilic one is held together by a series of strong and rather directional N + -HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds.

Related literature
For a description of the graph-set notation for hydrogenbonded aggregates, see: Grell et al. (1999). For basic stereochemistry terminology, see: Moss (1996). For the biological activity of the title compound, see: Hudson & Ismail (2001). For the crystal structure of a racemic mixture containing the title compound, see: Bashall et al. (2010). For previous work from our research group on the assembly of coordination polymers using phosphonic-based molecules, see: Cunha-Silva, Ananias et al.  Rocha et al. (2009) ;Shi, Cunha-Silva et al. (2008); . For a related structure, see: Fernandes et al. (2010). For a description of the TOPOS software, see: Blatov & Proserpio (2009 Table 1 Selected torsion angles ( ).
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2005); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2009); software used to prepare material for publication: SHELXTL.  The racemic mixture of the title compound is known as Ampropylfos and has been the object of several studies for its use as a pesticide (Hudson & Ismail, 2001), and its crystal structure has been very recently reported (Bashall et al., 2010).
The asymmetric unit is composed by two entities of the title compound in their zwitterionic form, in which the acidic phosphonate moiety donates one proton to the amino group ( Figure 1). The geometrical conformations of the two molecules are considerably different: in one unit the two torsion angles O3-P1-C1-C2 and P1-C1-C2-C3 are both +synclinal and in the other the analogous torsion angles (O6-P2-C4-C5 and P2-C4-C5-C6) are -synclinal and antiperiplanar, respectively (see Table 1; Moss, 1996). The two crystallographically unique molecules are organized in the crystal structure into a supramolecular bilayer (in the ab plane) having the hydrophilic portion in the interior (composed by the amino, methyne and phosphonate moieties) and the hydrophobic in the outer position (formed by the pendant -CH 2 CH 3 groups)

(Figures 2 and 3).
Inside the hydrophilic section, individual functional groups are disposed in a zigzag fashion along the [010] direction of the unit cell, leading to the formation of a supramolecular chain held together by a combination of four N + -H···O hydrogen bridges (green dashed bonds in Figure 2; Table 2) -graph set motif R 3 4 (10) (Grell et al., 1999). Supramolecular chains are, in turn, interconnected in the ab plane via the remanant N + -H···O (orange dashed lines in Figure 2) and O-H···O hydrogen bonds (violet dashed lines in Figure 2).
The crystal can be better described by employing a topological approach for the description of the aforementioned hydrogen bonding interactions. Taking the geometrical centre of each molecular unit as a node, and being the hydrogen bonding interactions the connections between nodes, the structure can be simplified into a two-dimensional uninodal 7-connected single-penetrated planar (4,4)IIIb network, with total Schläfli symbol 3 6 .4 12 .5 3 (Blatov & Proserpio, 2009 The title compound was purchased from Sigma-Aldrich (Aldrich, 98%) and was used as received without purification.
Suitable single crystals were grown from an aqueous solution over a period of one month.

Refinement
Hydrogen atoms bound to carbon were included in the final structural model using a riding-motion approximation with C-H = 1.00 Å (tertiary C-H), 0.99 Å (-CH 2 ) or 0.98 Å (terminal -CH 3 ). The isotropic thermal displacement parameters for these atoms were fixed at 1.2 (for the two former families) or 1.5 (for the terminal methyl group) times U eq of the respective parent atom.
Hydrogen atoms associated with the protonated -NH 3 + group or the pendant -OH moiety were directly located in difference Fourier maps and were included in the final structural 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 have been further restrained to 1.55 (1) Å in order to ensure a chemically reasonable geometry.
A total of 1730 estimated Friedel pairs have not been merged and were used as independent data for the structure refinement. The Flack parameter (Flack, 1983) converged to -0.03 (8), ultimately assuring a valid absolute structure determination from the single-crystal data set. Fig. 1. Asymmetric unit of the title compound showing the two crystallographically indenpendent molecular units. Thermal ellipsoids are drawn at the 80% probability level and the atomic labeling is provided for all non-hydrogen atoms. Hydrogen atoms are represented as small spheres with arbitrary radius.  Table 1. 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 )