4-Fluoro-2-(phospho­no­methyl)­benzene­sulfonic acid monohydrate

The title compound, C₇H₈FO₆PS·H₂O, contains both phospho­nic and sulfonic acid functionalities. An extensive network of O—H...O hydrogen bonds is present in the crystal structure. The three acidic protons are associated with the phospho­nate group. Two protons experience typical hydrogen-bond contacts with the sulfonate-O atoms, while the third has a longer covalent bond of 1.05 (3) Å to the phospho­nate-O atom and a short hydrogen-bond contact of 1.38 (3) Å to the water O atom (all O—H...O angles are in the range 162–175°). The sulfonate group is positioned so that one S—O bond is nearly coplanar with the phenyl ring [torsion angle O—S—C—C −8.6 (2)°]. The phospho­nate group is oriented approximately perpendicular to the ring [torsion angle P—C—C—C 99.2 (2)°] with one P—O bond anti to the benzyl C—C bond. The mol­ecules pack in layers in the b–c plane with the water mol­ecules in between adjacent pairs of inverted layers.

S1. Comment

The title compound, (I), was prepared as part of a study of fluorinated arylphosphonic acids and aryl sulfophosphonic acids (Montoneri, Savarino et al., 1994; Montoneri, Viscardi et al., 1994) and their metal salts (Langley et al., 1996; Benedetto et al., 1997). Compounds of this type are of interest, in part, for their ion exchange and proton-conducting potential (Alberti, Casciola et al., 1992; Alberti, Casciola, Palombari & Peraio, 1992). \sch

The central portion of the molecule (Fig. 1) is flat with the atoms of the ring showing an average deviation of 0.006 (2) Å from the least-squares plane and appended atoms all within 0.11 Å of the plane. The C1–C7 bond is rotated so that the phosphonic acid group is pointing away from the ring [torsion angle P–C7–C1–C6 - 76.9 (3)°] and one P–O bond is anti to the C1–C7 bond while the other two are gauche [torsion angle O4–P–C7–C1 - 59.9 (2)°]. The sulfonate group has one S–O bond almost eclipsing the ring, while the other two are in gauche positions [torsion angle O2–S–C2–C1 - 66.5 (2)°] and the methylene carbon is bent away from the sulfonate group by approximately 4° as is the methyl group in o-toluenesulfonic acid (Taga & Kobayashi, 1990). The three acidic protons are distributed in a manner which is consistent with the acid strengths of the functional groups. The phosphonate group retains two acidic protons, H4 and H5, with covalent O–H bonds of approximately 0.85 Å. The third acidic proton (H6) is located between one of the phosphonate O atoms and the water molecule, O–H 1.05 (3) Å, H···O 1.38 (3) Å. This arrangement fits on the continuum of O–H···O distances obtained in a recent study of such interactions (Steiner & Saenger, 1994). The lengths of the P–O bonds (Table 1) suggest that the O4–H4 and O5–H5 bonds are stronger than the O6–H6 bond. These data, together with the nearly equivalent S–O distances suggest a complete proton transfer from the stronger sulfonic acid to the weaker phosphonic acid, and a partial proton transfer from the latter function to the water molecule. Thus, the molecule actually exists in the solid state as a zwitterion that is intermediate between the two extremes ^-O₃SC₆H₃FCH₂PO₃H₃⁺·H₂O and ^-O₃SC₆H₃FCH₂PO₃H₂·H₃O⁺. This arrangement is consistent with the structure of o-toluenesulfonic acid dihydrate (Taga & Kobayashi, 1990) in which the acidic proton is fully transferred from the SO₃^- group to one of the water molecules to produce H₃O⁺. In the presence of the more basic phosphonate group in (I), the proton transfer is not complete and a symmetrical hydronium ion is not formed.

The molecules of (I) can be viewed as forming layers (Fig. 2) in the b-c plane which then stack in the a direction. The sulfonate and phosphonic acid groups are directed to opposite faces of the layer and the water molecules are located between every other pair of layers, closely associated with the phosphonic acid functionality. This packing scheme is somewhat different from what is observed for the isomeric 4-fluoro-3-sulfonatobenzylphosphonic acid hydrate (Benedetto et al., 1997). That structure also contains layers with the acidic groups on opposite faces, however the water molecules are associated with the sulfonate groups in between every pair of layers.

S2. Experimental

The procedure for the synthesis of (I) has been reported (Montoneri et al., 1994a).

S3. Refinement

The H atoms were located on difference electron-density maps and their positions refined with isotropic displacement parameters set at 1.2 times that of the attached atom at the time of their inclusion: C—H range: 0.90 (2)–0.99 (2) Å. Several of the O–H bond lengths refined to unrealistically short values (i.e. less than 0.8 Å) and were subsequently placed in fixed positions along the same O–H vector.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1991); program(s) used to solve structure: MITHRIL (Gilmore, 1983); program(s) used to refine structure: TEXSAN; molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures

	Fig. 1. An ORTEPII diagram (Johnson, 1976) showing the molecular structure and atom-labelling scheme of (I). Hydrogen bonds are shown by narrow lines. The displacement ellipsoids of the non-H atoms are shown at the 50% probability level.
	Fig. 2. An ORTEPII diagram (Johnson, 1976) showing the crystal packing of (I). The S and P atoms are shown with octant shading. Hydrogen bonds are shown by narrow lines. The displacement ellipsoids of the non-H atoms are shown at the 50% probability level.

(I)

Crystal data

C7H8FO6PS·H2O	Z = 2
Mr = 288.18	F(000) = 296
Triclinic, P1	Dx = 1.746 Mg m^−3
a = 8.486 (1) Å	Mo Kα radiation, λ = 0.7107 Å
b = 9.247 (3) Å	Cell parameters from 21 reflections
c = 7.917 (2) Å	θ = 19.7–22.6°
α = 104.84 (2)°	µ = 0.46 mm^−1
β = 110.00 (1)°	T = 296 K
γ = 97.37 (2)°	Slab, colorless
V = 548.1 (2) Å^3	0.30 × 0.30 × 0.10 mm

Data collection

Rigaku AFC6S diffractometer	1907 reflections with I > 0
Radiation source: X-ray tube	Rint = 0.021
Graphite monochromator	θmax = 25.0°
ω scans	h = 0→10
Absorption correction: ψ scan (North et al., 1968)	k = −10→10
Tmin = 0.908, Tmax = 0.955	l = −9→8
2051 measured reflections	3 standard reflections every 150 reflections
1909 independent reflections	intensity decay: −0.9%

Refinement

Refinement on F^2	0 constraints
Least-squares matrix: full	Only H-atom coordinates refined
R[F^2 > 2σ(F^2)] = 0.044	Weighting scheme based on measured s.u.'s w = 4Fo^2/σ^2(Fo^2)
wR(F^2) = 0.064	(Δ/σ)max = 0.016
S = 1.98	Δρmax = 0.40 e Å^−3
1907 reflections	Δρmin = −0.36 e Å^−3
173 parameters	Extinction correction: Zachariasen (1968) type 2 Gaussian isotropic
0 restraints	Extinction coefficient: 0.00000072 (22)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S	0.16148 (7)	0.36547 (7)	0.79116 (9)	0.0266 (2)
P	−0.36292 (8)	0.27677 (8)	0.63042 (9)	0.0285 (2)
F	−0.2588 (2)	0.0121 (2)	−0.0076 (2)	0.0488 (5)
O1	0.3305 (2)	0.4283 (2)	0.7930 (2)	0.0348 (5)
O2	0.0756 (2)	0.4859 (2)	0.8389 (3)	0.0401 (5)
O3	0.1784 (2)	0.2670 (2)	0.9095 (2)	0.0383 (5)
O4	−0.2632 (2)	0.4439 (2)	0.6785 (3)	0.0411 (6)
O5	−0.4344 (2)	0.2625 (2)	0.7823 (3)	0.0423 (6)
O6	−0.5080 (2)	0.2300 (2)	0.4394 (3)	0.0383 (5)
O7	−0.5051 (2)	0.2898 (2)	0.1603 (3)	0.0408 (5)
C1	−0.1330 (3)	0.1589 (3)	0.5020 (3)	0.0237 (6)
C2	0.0336 (3)	0.2490 (3)	0.5529 (3)	0.0242 (7)
C3	0.0991 (3)	0.2541 (3)	0.4160 (4)	0.0323 (8)
C4	0.0019 (3)	0.1738 (3)	0.2262 (4)	0.0362 (8)
C5	−0.1598 (3)	0.0890 (3)	0.1785 (3)	0.0328 (7)
C6	−0.2284 (3)	0.0777 (3)	0.3098 (4)	0.0304 (7)
C7	−0.2165 (3)	0.1538 (3)	0.6419 (4)	0.0274 (7)
H1	0.204 (3)	0.312 (3)	0.448 (3)	0.0381
H2	0.044 (3)	0.177 (3)	0.136 (4)	0.0429
H3	−0.341 (3)	0.022 (3)	0.273 (3)	0.0364
H4	−0.158	0.466	0.751	0.0496
H5	−0.507	0.316	0.792	0.0519
H6	−0.497 (3)	0.264 (3)	0.326 (4)	0.0459
H7A	−0.443	0.377	0.178	0.0495
H7B	−0.609	0.278	0.086	0.0495
H8	−0.139 (3)	0.185 (3)	0.778 (3)	0.0321
H9	−0.279 (3)	0.059 (3)	0.614 (3)	0.0321

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S	0.0181 (3)	0.0316 (4)	0.0273 (3)	0.0045 (3)	0.0068 (3)	0.0084 (3)
P	0.0202 (3)	0.0395 (4)	0.0284 (4)	0.0077 (3)	0.0104 (3)	0.0136 (3)
F	0.056 (1)	0.049 (1)	0.0262 (9)	0.0030 (8)	0.0078 (8)	0.0021 (7)
O1	0.0194 (9)	0.038 (1)	0.041 (1)	0.0008 (8)	0.0099 (8)	0.0088 (9)
O2	0.0281 (10)	0.038 (1)	0.043 (1)	0.0113 (9)	0.0100 (9)	−0.0011 (9)
O3	0.0303 (10)	0.048 (1)	0.031 (1)	0.0030 (9)	0.0030 (8)	0.0188 (9)
O4	0.0255 (10)	0.037 (1)	0.056 (1)	0.0092 (8)	0.0088 (9)	0.0160 (10)
O5	0.035 (1)	0.067 (1)	0.042 (1)	0.0232 (10)	0.0251 (9)	0.026 (1)
O6	0.0230 (10)	0.061 (1)	0.031 (1)	0.0087 (9)	0.0084 (8)	0.0196 (10)
O7	0.030 (1)	0.046 (1)	0.038 (1)	−0.0016 (9)	0.0028 (9)	0.0193 (9)
C1	0.022 (1)	0.024 (1)	0.027 (1)	0.009 (1)	0.010 (1)	0.010 (1)
C2	0.021 (1)	0.026 (1)	0.026 (1)	0.008 (1)	0.009 (1)	0.010 (1)
C3	0.025 (1)	0.039 (2)	0.036 (2)	0.007 (1)	0.014 (1)	0.015 (1)
C4	0.040 (2)	0.045 (2)	0.031 (2)	0.014 (1)	0.020 (1)	0.014 (1)
C5	0.038 (2)	0.031 (1)	0.023 (1)	0.010 (1)	0.007 (1)	0.004 (1)
C6	0.025 (1)	0.028 (1)	0.033 (2)	0.003 (1)	0.009 (1)	0.007 (1)
C7	0.022 (1)	0.029 (1)	0.031 (1)	0.004 (1)	0.010 (1)	0.012 (1)

Geometric parameters (Å, º)

S—O1	1.471 (2)	C3—C4	1.383 (4)
S—O2	1.447 (2)	C4—C5	1.363 (4)
S—O3	1.451 (2)	C5—C6	1.372 (3)
S—C2	1.776 (2)	O4—H4	0.84
P—O4	1.547 (2)	O5—H5	0.85
P—O5	1.546 (2)	O6—H6	1.05 (3)
P—O6	1.498 (2)	O7—H7A	0.85
P—C7	1.784 (3)	O7—H7B	0.85
F—C5	1.359 (3)	C3—H1	0.90 (2)
C1—C2	1.411 (3)	C4—H2	0.90 (2)
C1—C6	1.397 (3)	C6—H3	0.93 (2)
C1—C7	1.512 (3)	C7—H8	0.99 (2)
C2—C3	1.385 (3)	C7—H9	0.90 (2)
O1—S—O2	111.7 (1)	C1—C6—C5	119.8 (2)
O1—S—O3	110.5 (1)	P—C7—C1	110.6 (2)
O1—S—C2	105.9 (1)	P—O4—H4	116
O2—S—O3	113.4 (1)	P—O5—H5	115
O2—S—C2	107.1 (1)	P—O6—H6	122 (1)
O3—S—C2	107.9 (1)	H7A—O7—H7B	111
O4—P—O5	111.0 (1)	C2—C3—H1	120 (1)
O4—P—O6	109.0 (1)	C4—C3—H1	118 (1)
O4—P—C7	109.2 (1)	C3—C4—H2	121 (1)
O5—P—O6	110.0 (1)	C5—C4—H2	120 (1)
O5—P—C7	104.7 (1)	C1—C6—H3	118 (1)
O6—P—C7	112.8 (1)	C5—C6—H3	121 (1)
C2—C1—C6	117.5 (2)	P—C7—H8	105 (1)
C2—C1—C7	123.6 (2)	P—C7—H9	106 (1)
C6—C1—C7	118.8 (2)	C1—C7—H8	117 (1)
S—C2—C1	121.4 (2)	C1—C7—H9	111 (1)
S—C2—C3	118.0 (2)	H8—C7—H9	106 (2)
C1—C2—C3	120.6 (2)	O4—H4—O2	163
C2—C3—C4	120.9 (2)	O5—H5—O1	175
C3—C4—C5	117.9 (2)	O6—H6—O7	171 (2)
F—C5—C4	118.8 (2)	O7—H7A—O1	174
F—C5—C6	118.0 (2)	O7—H7B—O3	173
C4—C5—C6	123.2 (2)
S—C2—C1—C6	176.4 (2)	O3—S—C2—C3	−126.9 (2)
S—C2—C1—C7	0.3 (3)	O4—P—C7—C1	−59.9 (2)
S—C2—C3—C4	−175.9 (2)	O5—P—C7—C1	−178.8 (2)
P—C7—C1—C2	99.2 (2)	O6—P—C7—C1	61.5 (2)
P—C7—C1—C6	−76.9 (3)	C1—C2—C3—C4	1.3 (4)
F—C5—C4—C3	178.5 (2)	C1—C6—C5—C4	1.7 (4)
F—C5—C6—C1	−177.9 (2)	C2—C1—C6—C5	−0.7 (4)
O1—S—C2—C1	174.3 (2)	C2—C3—C4—C5	−0.3 (4)
O1—S—C2—C3	−8.6 (2)	C3—C2—C1—C6	−0.7 (3)
O2—S—C2—C1	−66.5 (2)	C3—C2—C1—C7	−176.8 (2)
O2—S—C2—C3	110.7 (2)	C3—C4—C5—C6	−1.2 (4)
O3—S—C2—C1	55.9 (2)	C5—C6—C1—C7	175.6 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O2	0.84	1.83	2.645 (2)	163
O5—H5···O1^i	0.85	1.83	2.678 (3)	175
O6—H6···O7	1.05 (3)	1.38 (3)	2.418 (2)	171 (2)
O7—H7A···O1^ii	0.85	1.85	2.695 (3)	174
O7—H7B···O3^iii	0.85	1.84	2.682 (2)	173

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