Ethane-1,1,2-tris­phospho­nic acid hemihydrate

Ethane-1,1,2-tris­phosphonic acid crystallizes as a hemihydrate, C₂H₉O₉P₃·0.5H₂O, in which the water O atom lies on an inversion centre in the space group P2₁/c. The acid com­ponent, which contains a short but noncentred O—H...O hydrogen bond, adopts a gauche conformation. The acid components are linked by an extensive series of O—H...O hydrogen bonds to form layers, which are linked into pairs by the water mol­ecules.

S1. Comment

The elaboration of new materials based on the supramolecular assembly of organic molecules constitutes a dynamic field of research (Desiraju, 1995 or???1998). Potential applications of such materials are diverse and include, as examples, materials for optics (Muthuraman et al., 1999) or for analytical purposes (Morin et al., 2005; Russell et al., 1997). Moreover, knowledge of supramolecular interactions can give crucial information to understand chemical transformations taking place in biochemical systems. Our first results in this area concern the study of the auto-assembly of mesitylene trisphosphonic acid (A), which forms dimer in the solid state (Jaffrès et al., 2002) characterized by the three methylenephosphic groups localized on the same side of the benzene ring. A second study has reported the cocrystallization of A with guanidinium chloride (Sopkova-de Oliveira Santos et al., 2004). More recently, we have reported the crystal structure of benzenetrisphosphonic acid (B), which was characterized by a packing involving both strong hydrogen bonds and π-stacking (Hix et al., 2007). These three studies contribute to show the potential of the phosphonic acid group to build supramolecular networks.

In order to study further the self-assembly of polyphosphonic derivatives, we have synthesized ethane-1,1,2-trisphosphonic acid (ETP1) from hexaethyl-1,1,2-tris(phosphonate), previously prepared following a method recently published (Delain-Bioton et al., 2005). ETP1 has a great potential to form supramolecular networks in view of the number of hydrogen-bond donor and acceptor sites. It is of note that ETP1 has been identified to be, among two other polyphosphonic compounds, highly effective for its covalent grafting on titanium oxide and for inducing calcium phosphate growth on its surface (Viornery et al., 2002). Therefore this molecule has a double interest: (1) it has a great potential to form supramolecular interactions by auto-assembly and (2) this compound is a good candidate for coating inorganic supports.

Crystals of ETP1.0.5H₂O suitable for diffraction were obtained after leaving ETP1 (initially a very viscous oil) for several weeks at room temperature. The asymmetric unit contains one molecule of ETP1 and one-half of a water molecule (Fig. 1). The water molecule is in special position on an inversion centre in the crystal structure, and the H atoms on the water molecule were difficult to locate from difference density map. The structure solution obtained from the refinement has two H atoms placed on the water atom O40 (the occupancy factor for each H atom being 1/2), two further H atoms with an occupancy of 0.50 being generated by the symmetry operation. Hence, four H atoms with an occupancy of 0.50 are present on the water O atom, illustrating the disorder associated with the exact position of H atoms in the structure in the solid state.

The acid component adopts a gauche conformation in the solid state, with a P2—C1—C2—P3 torsion angle of 78.88 (11)°. One internal hydrogen bond engaging two O atoms (O21 and H33/O33) bonded to P2 and P3, respectively, is observed, in which the O21···O33 contact distance corresponds to a strong hydrogen bond.

The P═O bond lengths are about 1.49 Å, and P—O bond lengths are between 1.5353 (14) and 1.5571 (10) Å, with the exception of the P2—O22 bond which is shorter [1.5160 (11) Å]. In the crystal structure, the P2—O22 bond is oriented face-to-face with another symmetric P2—O22 bond, and the two neighbouring O22 atoms are bound together by a hydrogen bond. The difference density map showed two peaks in proximity to atom O22, and so two positions for atom H22 have been attributed and refined, each position having an occupancy of 0.5. The nine O atoms of phosphonic groups are engaged in one or two hydrogen bonds with neighbouring ETP1 molecules or with the water molecules, thus completing the crystal packing. Molecules of ETP1 are packed along the crystallographic b axis by two hydrogen bonds (O11^v···H32—O32 and O31ⁱ···H12—O12; see Table 1 for symmetry codes) involving the phosphonic acid groups P1 and P3 of two symmetric molecules (Fig. 2). The O···O contact distances of these hydrogen bonds correspond to the normal range for this type of hydrogen bonding between phosphonic acid groups (Jaffrès et al., 2002). These chains formed along the b-axis direction are connected to another chain along the c axis (Fig. 3) via a hydrogen bond involving atoms O11 and O31 [no such bond in table] (Table 1).

Along the a-axis direction, the previously described layer in the bc plane is hydrogen bonded to another such layer (Fig. 3). The main bonding contribution to the cohesion of these double layers is the presence of a strong hydrogen bond occurring between the symmetrically related O22 atoms. The O22···H22—O22 distance is about 2.468 (2) Å. Additionally, there are weak hydrogen bonds involving the water molecule. Hence the packing is best described as two-dimensional (the a axis is the stacking direction).

In conclusion, ETP1.0.5H₂O adopts a gauche conformation in the solid state. The packing of this compound reveals the presence of chains running along the b axis involving intermolecular symmetrical O···H—O hydrogen bonds similar to those frequently observed for carboxylic acid. The chains are packed together via hydrogen bonds involving one molecule of water to finally define a two-dimensional structure. Furthermore, one intramolecular hydrogen bond, which certainly increases the stability of the observed gauche conformation, is noted. For the future, it will be interesting to study replacement of the molecule of water, which has a great importance in the packing, by other organic molecules to design new supramolecular networks.

Related literature

For related literature, see: Delain-Bioton, Turner, Lejeune, Villemin, Hix & Jaffrès (2005); Hix et al. (2007); Jaffrès et al. (2002); Morin et al. (2005); Muthuraman et al. (1999); Russell et al. (1997); Viornery et al. (2002).

S2. Experimental

Hexaethyl-1,1,2-triphosphonate (Delain-Bioton et al., 2005) (2.12 g, 4.84 mmol) and 60 ml of concentrated HCl (37% in water) were heated at reflux for 16 h. The resulting solution was concentrated in vacuo to dryness to produce a very viscous oil (1.72 g). Propylene oxide (1 ml) was added and the resulting mixture was again concentrated in vacuo. High vacuum pumping for 6 h led to the formation of a white powder (1.40 g). Dissolution in a mixture of methanol/acetone (2:1 v/v) gave a homogeneous solution. After slow evaporation at room temperature, a viscous oil was first obtained, which crystallized after five weeks. These crystals were collected by filtration and washed with methanol (yield 1.15 g, 88%). ¹H NMR (D₂O): 2.05 (m, 2H, CH₂P), 2.35 (m, 1H, PCCHP₂) p.p.m.; ³¹P NMR (D₂O): 21.2 (d, ³J_PP = 27 Hz, PCHP), 27.1 (t, ³J_PP = 27 Hz, PCH₂) p.p.m.; ¹³C NMR (D₂O): 22.8 (dt, ²J_CP = 130 Hz, ³J_CP < 1 Hz, PCH₂), 32.8 (dt, ²J_CP = 133 Hz, ³J_CP = 4 Hz, PCH₂) p.p.m.

S3. Refinement

H atoms bonded to C atoms were refined freely, giving C—H distances in the range 0.96 (2)–1.01 (2) Å. H atoms bonded to O atoms in the acid component were treated as riding atoms, with O—H distances 0.82 Å and U_iso(H) values of 1.5U_eq(O), with the exception of the H atom bonded to O22. The disorder in hydrogen occupancy on this O atom, was refined using two H-atom sites, H22A and H22B, each with an occupancy of 1/2, and the correct geometry was induced using DFIX and DANG restraints. A DFIX restraint was also used to refine the H atoms of water atom O40.

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXTL (Sheldrick, 1997b); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997a).

Figures

	Fig. 1. A displacement ellipsoid plot of the asymmetric unit of the crystal structure of (I) (with ellipsoids at the 50% probability level).
	Fig. 2. The packing of molecules of ETP1 along b axis. Dashed lines indicate hydrogen bonds. [Symmetry codes: (#) x, y + 1, z; (*) x, -y + 1/2, z - 1/2; (') x, -y - 1/2, z - 1/2.]
	Fig. 3. The packing of ETP1.0.5H2O, viewed down the c axis.

Ethane-1,1,2-trisphosphonic acid hemihydrate

Crystal data

C2H9O9P3·0.5H2O	F(000) = 572
Mr = 279.01	Dx = 1.944 Mg m^−3
Monoclinic, P21/c	Melting point = 443–445 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 12.5239 (3) Å	Cell parameters from 6782 reflections
b = 7.7987 (2) Å	θ = 3.1–37.6°
c = 10.3585 (3) Å	µ = 0.66 mm^−1
β = 109.523 (2)°	T = 273 K
V = 953.55 (4) Å^3	Prism, colourless
Z = 4	0.28 × 0.16 × 0.10 mm

Data collection

Bruker KAPPA APEXII CCD area-detector diffractometer	3691 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.032
Graphite monochromator	θmax = 37.6°, θmin = 3.1°
phi and ω scans	h = −21→20
40386 measured reflections	k = −13→13
5036 independent reflections	l = −17→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.095	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0376P)^2 + 0.659P] where P = (Fo^2 + 2Fc^2)/3
5036 reflections	(Δ/σ)max = 0.001
163 parameters	Δρmax = 0.58 e Å^−3
6 restraints	Δρmin = −0.60 e Å^−3

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	Occ. (<1)
P1	0.35630 (3)	−0.15959 (4)	1.14075 (3)	0.01782 (7)
O11	0.28892 (10)	−0.28971 (13)	1.18637 (11)	0.0254 (2)
O12	0.42406 (9)	−0.23325 (13)	1.05349 (11)	0.02425 (19)
H12	0.3972	−0.3261	1.0216	0.036*
O13	0.44966 (10)	−0.06870 (15)	1.25838 (11)	0.0277 (2)
H13	0.4228	−0.0349	1.3159	0.042*
P2	0.14130 (3)	−0.07597 (4)	0.90751 (4)	0.01949 (7)
O21	0.10554 (10)	0.04958 (14)	0.79166 (11)	0.0299 (2)
O22	0.05368 (10)	−0.12125 (15)	0.97354 (13)	0.0297 (2)
H22A	0.085 (3)	−0.134 (6)	1.0555 (19)	0.045*	0.50
H22B	0.021 (4)	−0.034 (4)	0.984 (5)	0.045*	0.50
O23	0.17534 (10)	−0.25116 (13)	0.86048 (11)	0.0268 (2)
H23	0.2074	−0.2345	0.8043	0.040*
P3	0.28276 (3)	0.35066 (4)	0.96192 (4)	0.02229 (8)
O31	0.36808 (10)	0.47252 (12)	0.94221 (11)	0.0256 (2)
O32	0.25165 (13)	0.39835 (15)	1.09043 (15)	0.0405 (3)
H32	0.2708	0.4976	1.1126	0.061*
O33	0.17315 (13)	0.34834 (16)	0.83786 (18)	0.0522 (4)
H33	0.1529	0.2489	0.8184	0.078*
C1	0.26544 (11)	0.00902 (15)	1.04236 (13)	0.0182 (2)
H1	0.2343 (18)	0.067 (3)	1.109 (2)	0.034 (6)*
C2	0.33800 (12)	0.13700 (16)	0.99285 (15)	0.0217 (2)
H2A	0.3464 (17)	0.095 (3)	0.908 (2)	0.031 (5)*
H2B	0.411 (2)	0.149 (3)	1.063 (2)	0.044 (6)*
O40	0.0000	0.0000	0.5000	0.0756 (9)
H40A	0.059 (5)	0.025 (11)	0.458 (8)	0.113*	0.50
H40B	0.046 (6)	0.022 (11)	0.597 (3)	0.113*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.02338 (16)	0.01356 (12)	0.01926 (13)	−0.00020 (10)	0.01075 (11)	0.00031 (10)
O11	0.0368 (6)	0.0176 (4)	0.0289 (5)	−0.0020 (4)	0.0204 (4)	0.0021 (3)
O12	0.0287 (5)	0.0193 (4)	0.0306 (5)	−0.0005 (4)	0.0177 (4)	−0.0035 (3)
O13	0.0298 (5)	0.0302 (5)	0.0222 (4)	−0.0031 (4)	0.0074 (4)	−0.0051 (4)
P2	0.02006 (15)	0.01592 (13)	0.02458 (15)	−0.00113 (11)	0.01022 (12)	−0.00247 (11)
O21	0.0346 (6)	0.0233 (5)	0.0268 (5)	−0.0038 (4)	0.0033 (4)	0.0019 (4)
O22	0.0266 (5)	0.0286 (5)	0.0413 (6)	−0.0024 (4)	0.0212 (5)	−0.0027 (5)
O23	0.0338 (5)	0.0191 (4)	0.0330 (5)	−0.0016 (4)	0.0181 (4)	−0.0070 (4)
P3	0.02675 (17)	0.01228 (12)	0.02906 (17)	−0.00093 (11)	0.01095 (13)	0.00018 (11)
O31	0.0374 (6)	0.0154 (4)	0.0304 (5)	−0.0029 (4)	0.0197 (4)	−0.0001 (3)
O32	0.0602 (9)	0.0212 (5)	0.0594 (8)	−0.0109 (5)	0.0455 (7)	−0.0089 (5)
O33	0.0443 (8)	0.0190 (5)	0.0675 (10)	0.0017 (5)	−0.0158 (7)	−0.0010 (5)
C1	0.0224 (5)	0.0129 (4)	0.0222 (5)	−0.0013 (4)	0.0113 (4)	−0.0011 (4)
C2	0.0238 (6)	0.0145 (5)	0.0295 (6)	−0.0008 (4)	0.0125 (5)	0.0025 (4)
O40	0.0630 (17)	0.114 (2)	0.0435 (13)	−0.0343 (18)	0.0094 (12)	−0.0088 (15)

Geometric parameters (Å, º)

P1—O11	1.4939 (10)	P3—O31	1.4942 (11)
P1—O12	1.5427 (10)	P3—O33	1.5353 (14)
P1—O13	1.5498 (11)	P3—O32	1.5519 (12)
P1—C1	1.8132 (13)	P3—C2	1.7916 (13)
O12—H12	0.8200	O32—H32	0.8200
O13—H13	0.8200	O33—H33	0.8200
P2—O21	1.4967 (11)	C1—C2	1.5480 (17)
P2—O22	1.5160 (11)	C1—H1	1.01 (2)
P2—O23	1.5571 (10)	C2—H2A	0.97 (2)
P2—C1	1.8320 (13)	C2—H2B	0.96 (2)
O22—H22A	0.814 (18)	O40—H40A	1.00 (2)
O22—H22B	0.818 (18)	O40—H40B	0.99 (2)
O23—H23	0.8200
O11—P1—O12	114.33 (6)	O33—P3—O32	108.08 (10)
O11—P1—O13	114.80 (6)	O31—P3—C2	111.40 (6)
O12—P1—O13	102.29 (6)	O33—P3—C2	108.82 (7)
O11—P1—C1	110.83 (6)	O32—P3—C2	105.20 (7)
O12—P1—C1	107.79 (6)	P3—O32—H32	109.5
O13—P1—C1	106.09 (6)	P3—O33—H33	109.5
P1—O12—H12	109.5	C2—C1—P1	109.04 (9)
P1—O13—H13	109.5	C2—C1—P2	115.04 (9)
O21—P2—O22	116.51 (7)	P1—C1—P2	112.30 (6)
O21—P2—O23	111.28 (6)	C2—C1—H1	110.1 (12)
O22—P2—O23	104.59 (6)	P1—C1—H1	104.6 (12)
O21—P2—C1	108.96 (6)	P2—C1—H1	105.1 (12)
O22—P2—C1	107.34 (7)	C1—C2—P3	115.12 (9)
O23—P2—C1	107.74 (6)	C1—C2—H2A	109.6 (12)
P2—O22—H22A	109.2 (19)	P3—C2—H2A	107.5 (12)
P2—O22—H22B	110 (2)	C1—C2—H2B	108.8 (14)
H22A—O22—H22B	93 (5)	P3—C2—H2B	104.8 (14)
P2—O23—H23	109.5	H2A—C2—H2B	110.9 (18)
O31—P3—O33	111.92 (8)	H40A—O40—H40B	98 (5)
O31—P3—O32	111.15 (6)
P2—C1—C2—P3	78.88 (11)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O12—H12···O31^i	0.82	1.75	2.5584 (14)	167
O13—H13···O31^ii	0.82	1.74	2.5559 (15)	177
O22—H22B···O22^iii	0.82 (2)	1.68 (2)	2.486 (2)	169 (3)
O23—H23···O11^iv	0.82	1.85	2.6632 (14)	175
O32—H32···O11^v	0.82	1.81	2.6103 (15)	165
O33—H33···O21	0.82	1.65	2.4706 (16)	174
O40—H40A···O33^vi	1.00 (2)	2.40 (3)	3.370 (2)	165 (7)
O40—H40A···O32^vi	1.00 (2)	2.42 (7)	3.0767 (16)	123 (6)
O40—H40B···O21	0.99 (2)	1.92 (3)	2.8905 (11)	167 (8)

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