(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.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.025
• wR factor = 0.070
• Data-to-parameter ratio = 32.9

checkCIF/PLATON results

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Alert level C
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           36.29
           From the CIF: _reflns_number_total               2535
           Count of symmetry unique reflns         1486
           Completeness (_total/calc)            170.59%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1049
           Fraction of Friedel pairs measured     0.706
           Are heavy atom types Z>Si present        yes

Author Response: A total number of 1051 estimated Friedel pairs have not been merged and were used as independent data for the overall structure refinement.

PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          7

Author Response: Please see the dedicated experimental section in the main paper for further details on the structure solution and refinement.

PLAT791_ALERT_4_G Note: The Model has Chirality at C1     (Verify)          R

Author Response: The chirality of the indicated carbon atoms is correct.

PLAT850_ALERT_4_G Check Flack Parameter Exact Value 0.00 and su ..       0.08

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   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
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Author Response: This crystallographic communication results from a research effort which involves three distinct research groups from two Research Units. Thus, all researchers contribute either with their work and/or financial support, hence the presence of more than five authors, of which four are supervisors. All authors contributed actively in the exchange of ideas and in the writing up of this short crystallographic communication.

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S1. Comment

The title compound, R-1-aminoethylphosphonic acid (C₂H₈NO₃P), 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). Following our interest in the use of phosphonic acid molecules in the construction of multi-dimensional coordination polymers (Cunha-Silva, Ananias et al., 2009; Cunha-Silva, Lima et al., 2009; Shi, Cunha-Silva et al., 2008; Shi, Trindade et al., 2008), herein we wish to describe the crystal structure of the title compound.

The title compound crystallises in its zwitterionic form in which the acidic phosphonate moiety donates one proton to the amino group (Fig. 1). Individual molecular units are disposed in a zigzag fashion along the [100] direction of the unit cell, leading to the formation of a supramolecular chain held together by a combination of the inner ···O1···H1—N1⁺—H3··· hydrogen bonds [graph set motif C¹₂(4), Grell et al. (1999) - green dashed bonds in 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 —CH₃ groups which point toward each other.

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. (2009); Cunha-Silva, Lima et al. (2009); Shi, Cunha-Silva et al. (2008); Shi, Trindade et al. (2008).

S2. 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.

¹H-NMR (300.13 MHz, D₂O) δ: 1.27 (dd, 3H, J(¹H-¹H) = 7.3 Hz and J(¹H-³¹P)= 14.8 Hz, CH₃) and 3.19 (dq, 1H, J(¹H-¹H)= 7.3 Hz and J(¹H-³¹P) = 12.7 Hz, CH).

¹³C-NMR (75.47 MHz, D₂O) δ: 16.4 (d, J(¹³C-³¹P) = 2.6 Hz,CH₃) and 47.6 (d, J(¹³C-³¹P) = 145.1 Hz,CH).

³¹P-NMR (121.49 MHz, D₂O) δ: 14.8 (dq, J(³¹P-¹H) = 13.8 and 14.6 Hz).

S3. Refinement

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 (–CH₃). 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 —NH₃⁺ 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 —NH₃⁺ terminal group were further restrained to 1.55 (1) Å in order to ensure a chemically reasonable geometry for this moiety.

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2006); data reduction: SAINT-Plus (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2009); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. Molecular structure of the title compound. Displacement ellipsoids are drawn at the 80% probability level and the atomic labeling is provided for all non-hydrogen atoms.
	Fig. 2. Supramolecular one-dimensional zigzag chain running parallel to the [100] direction of the unit cell. The inner N—H···O interactions composing the graph set motif C^12(4) are represented as dashed green lines, while the outer O—H···O bonds as violet dashed green lines. For hydrogen bonding geometrical details see Table 1. Symmetry operations used to generate equivalent atoms have been omitted for simplicity.
	Fig. 3. Crystal packing of the title compound viewed in perspective along the [100] direction of the unit cell. Hydrogen bonds are represented as dashed green (intra-chain N—H···O type), violet (O—H···O) or orange (inter-chain N—H···O interactions) lines.

(R)-(1-Ammonioethyl)phosphonate

Crystal data

C2H8NO3P	F(000) = 264
Mr = 125.06	Dx = 1.583 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 3869 reflections
a = 4.8256 (1) Å	θ = 2.8–35.9°
b = 10.3928 (3) Å	µ = 0.42 mm^−1
c = 10.4668 (3) Å	T = 150 K
V = 524.93 (2) Å^3	Prism, colourless
Z = 4	0.12 × 0.08 × 0.04 mm

Data collection

Bruker X8 Kappa CCD APEXII diffractometer	2535 independent reflections
Radiation source: fine-focus sealed tube	2362 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
ω and phi scans	θmax = 36.3°, θmin = 3.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1997)	h = −7→8
Tmin = 0.951, Tmax = 0.983	k = −16→17
7972 measured reflections	l = −17→16

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.025	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.070	w = 1/[σ^2(Fo^2) + (0.0415P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
2535 reflections	Δρmax = 0.50 e Å^−3
77 parameters	Δρmin = −0.26 e Å^−3
7 restraints	Absolute structure: Flack (1983), 1051 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.00 (8)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
P1	0.12299 (5)	0.08570 (2)	0.11153 (2)	0.01023 (6)
O1	0.15178 (17)	0.13133 (7)	−0.02404 (7)	0.01436 (13)
O2	0.33072 (15)	−0.02579 (7)	0.14607 (8)	0.01551 (14)
H4	0.512 (2)	0.0009 (18)	0.1437 (15)	0.023*
O3	−0.16015 (15)	0.03922 (8)	0.15035 (8)	0.01671 (15)
N1	0.15332 (19)	0.34471 (8)	0.15951 (8)	0.01264 (14)
H1	0.290 (2)	0.3648 (15)	0.0983 (11)	0.019*
H2	0.152 (3)	0.4080 (12)	0.2239 (10)	0.019*
H3	−0.0211 (19)	0.3439 (15)	0.1171 (13)	0.019*
C1	0.2286 (2)	0.21731 (10)	0.21766 (9)	0.01326 (17)
H1A	0.4352	0.2143	0.2248	0.016*
C2	0.1111 (4)	0.20387 (11)	0.35212 (10)	0.0253 (2)
H2A	0.1924	0.2698	0.4075	0.038*
H2B	0.1557	0.1184	0.3858	0.038*
H2C	−0.0906	0.2148	0.3495	0.038*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.00725 (9)	0.01088 (9)	0.01254 (9)	−0.00054 (8)	−0.00037 (8)	0.00118 (8)
O1	0.0141 (3)	0.0168 (3)	0.0121 (3)	−0.0005 (3)	−0.0003 (3)	0.0012 (2)
O2	0.0087 (3)	0.0130 (3)	0.0248 (4)	0.0004 (2)	−0.0024 (2)	0.0025 (3)
O3	0.0076 (3)	0.0195 (3)	0.0229 (3)	−0.0017 (2)	0.0002 (3)	0.0051 (3)
N1	0.0126 (3)	0.0122 (3)	0.0132 (3)	0.0000 (3)	0.0000 (3)	−0.0004 (3)
C1	0.0134 (4)	0.0137 (4)	0.0126 (4)	−0.0001 (3)	−0.0025 (3)	0.0011 (3)
C2	0.0425 (7)	0.0216 (5)	0.0118 (4)	0.0001 (5)	0.0004 (5)	0.0019 (4)

Geometric parameters (Å, º)

P1—O1	1.5025 (8)	N1—H2	0.942 (7)
P1—O3	1.5051 (8)	N1—H3	0.951 (7)
P1—O2	1.5742 (8)	C1—C2	1.5238 (16)
P1—C1	1.8344 (10)	C1—H1A	1.0000
O2—H4	0.918 (9)	C2—H2A	0.9800
N1—C1	1.5018 (13)	C2—H2B	0.9800
N1—H1	0.943 (8)	C2—H2C	0.9800
O1—P1—O3	116.12 (4)	N1—C1—C2	111.41 (9)
O1—P1—O2	112.98 (4)	N1—C1—P1	110.17 (6)
O3—P1—O2	106.25 (4)	C2—C1—P1	112.80 (8)
O1—P1—C1	108.11 (5)	N1—C1—H1A	107.4
O3—P1—C1	109.15 (5)	C2—C1—H1A	107.4
O2—P1—C1	103.46 (4)	P1—C1—H1A	107.4
P1—O2—H4	112.2 (12)	C1—C2—H2A	109.5
C1—N1—H1	107.5 (10)	C1—C2—H2B	109.5
C1—N1—H2	109.1 (9)	H2A—C2—H2B	109.5
H1—N1—H2	109.6 (9)	C1—C2—H2C	109.5
C1—N1—H3	113.3 (10)	H2A—C2—H2C	109.5
H1—N1—H3	107.7 (9)	H2B—C2—H2C	109.5
H2—N1—H3	109.5 (10)
O1—P1—C1—N1	33.30 (8)	O1—P1—C1—C2	158.48 (8)
O3—P1—C1—N1	−93.86 (7)	O3—P1—C1—C2	31.32 (10)
O2—P1—C1—N1	153.33 (7)	O2—P1—C1—C2	−81.49 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H4···O3^i	0.92 (1)	1.63 (1)	2.5484 (10)	175 (2)
N1—H1···O1^ii	0.94 (1)	1.91 (1)	2.8033 (11)	157 (1)
N1—H2···O3^iii	0.94 (1)	1.90 (1)	2.8369 (12)	178 (1)
N1—H3···O1^iv	0.95 (1)	1.87 (1)	2.8160 (12)	171 (1)

Symmetry codes: (i) x+1, y, z; (ii) x+1/2, −y+1/2, −z; (iii) −x, y+1/2, −z+1/2; (iv) x−1/2, −y+1/2, −z.