rac-1-Phenyl­ethyl­ammonium carboxy­methyl­phospho­nate(1-): hydrogen-bonded anion sheets with pendent cations

In the title compound, C₈H₁₂N⁺·C₂H₄O₅P^-, the anions are linked by two O-H...O hydrogen bonds [H...O both 1.75 Å, O...O = 2.5781 (15) and 2.5834 (15) Å, and O-H...O = 169 and 176°] into sheets built from alternating (8) and (32) rings. Each cation is linked to an anion sheet by three N-H...O hydrogen bonds [H...O = 1.88-2.04 Å, N...O = 2.7603 (16)-2.9334 (17) Å and N-H...O = 162-166°], such that all the cations pendent from one face of the sheet are of the R configuration, while all those pendent from the opposite face are of the S configuration.

S1. Comment

The structures of carboxymethylphosphonic acid [HOOCCH₂P(O)(OH)₂] and its ammonium salt [NH₄]⁺·[C₂H₄O₅P]⁻ were reported several years ago (Lis, 1997), and since then the supramolecular structures have been reported for a number of salts formed by reaction of this acid with a range of organic diamines (Farrell et al., 2001; Videnova-Adrabinska, 2002; Bowes et al., 2003). We report here the supramolecular structure of the salt, (I), formed with a racemic chiral mono-amine, 2-phenylethylamine.

Compound (I) is a salt, [PhCH(CH₃)NH₃]⁺·[HOOCCH₂P(O)₂OH]⁻ (Fig. 1), in which one H atom has been fully transferred to the amine from a POH unit of the acid; in the anion the C—O and P—O distances (Table 1) are fully consistent with the locations of the associated H atoms as deduced from difference maps. The O—P—O angle involving the two unprotonated O atoms (O3 and O4) is significantly larger than the other O—P—O angles, and it is balanced by the correspondingly small O5—P1—C2 angle. The remaining bond distances and interbond angles show no unusual features. The centrosymmetric space group accommodates equal numbers of (R) and (S) cations, and the asymmetric unit was selected to include a cation of (R) configuration.

The two-dimensional anion substructure is readily analysed in terms of the actions of the two independent O—H···O hydrogen bonds (Table 2), and it is convenient to consider these in turn. Phosphonic atom O5 in the anion at (x, y, z) acts as a hydrogen-bond donor to phosphonate atom O3 in the anion at (1 − x, 1 − y, 1 − z), so generating a centrosymmetric R²₂(8) ring, centred at (1/2, 1/2, 1/2). The action of the second O—H···O hydrogen bond is then readily analysed in terms of the linking of the R²₂(8) dimers. Carboxy atoms O1 in the anions at (x, y, z) and (1 − x, 1 − y, 1 − z), which form the (1/2, 1/2, 1/2) dimer, act as hydrogen-bond donors to phosphonate atoms O4 at (x, 0.5 − y, −0.5 + z) and (1 − x, 0.5 + y, 1.5 − z), respectively, which are themselves components of the dimers centred at (1/2, 0, 0) and (1/2, 1, 10), respectively. Similarly, the two O4 atoms in the (1/2, 1/2, 1/2) dimer accept hydrogen bonds from carboxy atoms O1 in the anions at (x, 0.5 − y, 0.5 + z) and (1 − x, 0.5 + y, 0.5 − z), themselves components of the dimers centred at (1/2, 0, 1) and (1/2, 1, 0), respectively.

In this way, the two O—H···O hydrogen bonds generate a (100) sheet of anions built from alternating R²₂(8) and R⁶₆(32) rings, where both ring types are centrosymmetric (Fig. 2). The R²₂(8) rings are centred at (1/2, m, n) and (1/2, m + 1/2, n + 1/2), and the R⁶₆(32) rings are centred at (1/2, m, n + 1/2) and (1/2, m + 1/2, n) (where m and n independently take the value zero or integer). A single sheet of this type passes through each unit cell. The two-dimensional anion substructure of (I) is thus the same as that observed in the imidazolium salt (Videnova-Adrabinska, 2002) but differs from that found in the salt formed with 1,2-bis(4'-pyridyl)ethane, where the anion sheets consist of alternating R²₂(12) and R⁶₆(28) rings (Bowes et al., 2003). A more common occurrence of the R²₂(8) motif in salts with diamines is as a component of one-dimensional anion substructures including chains of spiro-fused rings and chains of edge-fused rings (Bowes et al., 2003).

The cation in (I) is linked to the anion sheet in a multi-point interaction; the acceptors in the three N—H···O hydrogen bonds are provided to three different anions, all lying in the same (100) sheet (Table 2). Because the anion sheet is centrosymmetric, all of the cations pendent from one face of the sheet have the (R) configuration, while all those pendent from the opposite face of the same sheet have the (S) configuration. Two cations, one (R) and one (S), lie over each R⁶₆(32) ring and their effect is to divide this ring into five sectors, viz. one centrosymmetric R⁴₆(16) ring and a pair each of R²₃(10) and R³₃(12) rings (Fig. 2). The (100) sheet is thus tripartite in nature, with a polar central layer between lipophilic outer layers comprising methyl and phenyl groups (Fig. 3). A rather similar overall structure was observed in the imidazolium salt, although with only two-point attachment of the cations to the anion sheet.

Adjacent (100) sheets are linked weakly by a single C—H···π(arene) hydrogen bond (Table 2); atom C2 in the anion at (x, y, z), part of the sheet centred at x = 1/2, acts as a hydrogen-bond donor, via atom H2B, to the phenyl ring of the cation at (-x, 0.5 + y, 0.5 − z), which forms part of the sheet centred at x = −0.5. Propagation by inversion of this interaction links all of the (100) sheets into a single three-dimensional framework structure.

All of the hard (Desiraju & Steiner, 1999) hydrogen bonds in (I) have D—H···A units that are almost linear and the O—H···O hydrogen bonds are short for their type. It remains a moot point whether the formation of the anion substructure is controlled primarily by the short strong O—H···O hydrogen bonds, or whether the cations provide some significant direction to the structure-assembly process; the formation of the same anion substructure in the presence of two very different cations, imidazolium and 2-phenylethylammonium, perhaps argues against the cation-template effect previously suggested (Videnova-Adrabinska, 2002).

S2. Experimental

Equimolar quantities of racemic 2-phenylethylamine and carboxymethylphosphonic acid were dissolved separately in methanol The solutions were mixed and the mixture was then set aside to crystallize, providing analytically pure (I). Analysis found: C 45.9, H 6.6, N 5.7%; C₁₀H₁₆NO₅P requires: C 46.0, H 6.2, N 5.4%. Crystals suitable for single-crystal X-ray diffraction were selected directly from the prepared sample.

S3. Refinement

Space group P2₁/c was uniquely assigned from the systematic absences. All H atoms were located from difference maps and were thereafter treated as riding atoms, with C—H distances of 0.95 (aromatic), 0.98 (CH₃), 0.99 (CH₂) and 1.00 Å (aliphatic CH), N—H distances of 0.91 Å, and O—H distances of 0.84 Å.

Computing details

Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997); data reduction: DENZO–SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997) and PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. The independent components of (I), showing the (R) enantiomorph of the cation, with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. Part of the crystal structure of (I), showing (a) the formation of the anion sheet and (b) the linking of the cations to the anion sheet. For clarity, the hydrocarbyl component of the cations, and H atoms bonded to C atoms in the anions, have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign () or an ampersand (&) are at the symmetry positions (1 − x, 1 − y, 1 − z), (1 − x, −0.5 + y, 0.5 − z), (x, 0.5 − y, −0.5 + z) and (1 − x, 0.5 + y, 0.5 − z), respectively.
	Fig. 3. A stereoview of part of the crystal structure of (I), showing the tripartite nature of the (100) sheets and the C—H···π(arene) hydrogen bond linking adjacent sheets. For clarity, H atoms bonded to C atoms, but not involved in the motif shown, have been omitted.

rac-2-Phenylethylammonium carboxymethylphosphonate(1-)

Crystal data

C8H12N^+·C2H4O5P^−	F(000) = 552
Mr = 261.21	Dx = 1.394 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2845 reflections
a = 8.2969 (3) Å	θ = 2.9–27.5°
b = 13.6898 (3) Å	µ = 0.23 mm^−1
c = 11.0388 (4) Å	T = 150 K
β = 96.7869 (18)°	Plate, colourless
V = 1245.03 (7) Å^3	0.28 × 0.18 × 0.08 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	2394 reflections with I > 2σ(I)
Radiation source: fine-focus sealed X-ray tube	Rint = 0.039
Graphite monochromator	θmax = 27.5°, θmin = 2.9°
ϕ scans, and ω scans with κ offsets	h = −10→10
10538 measured reflections	k = −15→17
2845 independent reflections	l = −14→14

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)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.095	w = 1/[σ^2(Fo^2) + (0.0401P)^2 + 0.6945P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
2845 reflections	Δρmax = 0.30 e Å^−3
159 parameters	Δρmin = −0.33 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0076 (19)

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

	x	y	z	Uiso*/Ueq
P1	0.40173 (5)	0.36759 (3)	0.44266 (3)	0.01881 (13)
O1	0.29772 (17)	0.29493 (8)	0.15716 (11)	0.0320 (3)
O2	0.40129 (15)	0.44255 (8)	0.13225 (10)	0.0278 (3)
O3	0.35709 (14)	0.42341 (8)	0.55175 (9)	0.0234 (3)
O4	0.39058 (14)	0.25824 (8)	0.45235 (9)	0.0250 (3)
O5	0.57737 (13)	0.39345 (8)	0.41434 (10)	0.0233 (3)
C1	0.32976 (18)	0.38536 (11)	0.19124 (13)	0.0205 (3)
C2	0.2695 (2)	0.41036 (12)	0.31071 (14)	0.0249 (3)
N1	0.35240 (15)	0.09402 (9)	0.30670 (11)	0.0202 (3)
C11	0.05149 (19)	0.10557 (11)	0.29944 (15)	0.0249 (3)
C12	−0.0543 (2)	0.13605 (16)	0.3801 (2)	0.0461 (5)
C13	−0.2009 (3)	0.18031 (18)	0.3377 (3)	0.0663 (8)
C14	−0.2423 (3)	0.19524 (15)	0.2149 (3)	0.0636 (8)
C15	−0.1371 (3)	0.16794 (16)	0.1346 (2)	0.0551 (7)
C16	0.0095 (2)	0.12237 (14)	0.17573 (17)	0.0351 (4)
C17	0.20171 (19)	0.04885 (11)	0.34650 (14)	0.0234 (3)
C18	0.1913 (2)	−0.05743 (12)	0.30635 (19)	0.0352 (4)
H1	0.3347	0.2842	0.0908	0.048*
H5	0.5956	0.4530	0.4284	0.035*
H2A	0.1605	0.3814	0.3123	0.030*
H2B	0.2583	0.4822	0.3162	0.030*
H1A	0.3682	0.1542	0.3412	0.030*
H1B	0.3405	0.0998	0.2240	0.030*
H1C	0.4395	0.0553	0.3309	0.030*
H12	−0.0263	0.1266	0.4653	0.055*
H13	−0.2729	0.2003	0.3939	0.080*
H14	−0.3435	0.2244	0.1859	0.076*
H15	−0.1642	0.1802	0.0500	0.066*
H16	0.0808	0.1028	0.1190	0.042*
H17	0.2124	0.0503	0.4377	0.028*
H18A	0.1829	−0.0608	0.2172	0.053*
H18B	0.0953	−0.0877	0.3344	0.053*
H18C	0.2889	−0.0922	0.3416	0.053*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0262 (2)	0.0155 (2)	0.0153 (2)	−0.00028 (14)	0.00470 (14)	−0.00098 (14)
O1	0.0533 (8)	0.0220 (6)	0.0230 (6)	−0.0106 (5)	0.0142 (5)	−0.0046 (5)
O2	0.0374 (7)	0.0238 (6)	0.0217 (6)	−0.0075 (5)	0.0010 (5)	0.0024 (4)
O3	0.0335 (6)	0.0200 (5)	0.0183 (5)	−0.0026 (4)	0.0091 (4)	−0.0027 (4)
O4	0.0398 (7)	0.0161 (5)	0.0194 (5)	−0.0020 (4)	0.0051 (5)	−0.0003 (4)
O5	0.0259 (6)	0.0214 (5)	0.0234 (5)	−0.0004 (4)	0.0064 (4)	−0.0037 (4)
C1	0.0223 (7)	0.0202 (7)	0.0182 (7)	0.0014 (6)	−0.0014 (6)	0.0007 (6)
C2	0.0284 (8)	0.0248 (8)	0.0216 (7)	0.0066 (6)	0.0037 (6)	−0.0019 (6)
N1	0.0238 (7)	0.0173 (6)	0.0195 (6)	−0.0004 (5)	0.0026 (5)	−0.0009 (5)
C11	0.0236 (8)	0.0192 (7)	0.0316 (8)	−0.0021 (6)	0.0022 (6)	−0.0012 (6)
C12	0.0321 (10)	0.0553 (13)	0.0513 (12)	0.0009 (9)	0.0063 (9)	−0.0264 (10)
C13	0.0289 (11)	0.0528 (14)	0.117 (2)	0.0046 (9)	0.0087 (13)	−0.0476 (16)
C14	0.0276 (11)	0.0228 (9)	0.134 (3)	0.0009 (8)	−0.0152 (14)	0.0002 (12)
C15	0.0353 (11)	0.0455 (12)	0.0782 (16)	−0.0146 (9)	−0.0201 (11)	0.0343 (12)
C16	0.0278 (9)	0.0392 (10)	0.0368 (10)	−0.0087 (7)	−0.0021 (7)	0.0147 (8)
C17	0.0255 (8)	0.0253 (8)	0.0196 (7)	−0.0019 (6)	0.0042 (6)	0.0033 (6)
C18	0.0308 (9)	0.0213 (8)	0.0539 (12)	−0.0016 (7)	0.0070 (8)	0.0045 (8)

Geometric parameters (Å, º)

P1—O3	1.5088 (11)	C11—C16	1.388 (2)
P1—O4	1.5043 (11)	C11—C17	1.508 (2)
P1—O5	1.5667 (11)	C12—C13	1.390 (3)
P1—C2	1.8137 (16)	C12—H12	0.95
C1—O1	1.3120 (18)	C13—C14	1.374 (4)
C1—O2	1.2167 (19)	C13—H13	0.95
O1—H1	0.84	C14—C15	1.367 (4)
O5—H5	0.84	C14—H14	0.95
C1—C2	1.504 (2)	C15—C16	1.394 (3)
C2—H2A	0.99	C15—H15	0.95
C2—H2B	0.99	C16—H16	0.95
N1—C17	1.5062 (19)	C17—C18	1.520 (2)
N1—H1A	0.91	C17—H17	1.00
N1—H1B	0.91	C18—H18A	0.98
N1—H1C	0.91	C18—H18B	0.98
C11—C12	1.386 (3)	C18—H18C	0.98
O3—P1—O4	115.10 (6)	C11—C12—H12	119.7
O4—P1—O5	107.79 (6)	C13—C12—H12	119.7
O5—P1—O3	111.51 (6)	C14—C13—C12	120.2 (2)
O3—P1—C2	107.18 (7)	C14—C13—H13	119.9
O4—P1—C2	109.99 (7)	C12—C13—H13	119.9
O5—P1—C2	104.79 (7)	C15—C14—C13	119.6 (2)
C1—O1—H1	109.5	C15—C14—H14	120.2
P1—O5—H5	109.5	C13—C14—H14	120.2
O2—C1—O1	123.29 (14)	C14—C15—C16	120.7 (2)
O2—C1—C2	123.81 (14)	C14—C15—H15	119.6
O1—C1—C2	112.90 (13)	C16—C15—H15	119.6
C1—C2—P1	113.50 (11)	C11—C16—C15	120.1 (2)
C1—C2—H2A	108.9	C11—C16—H16	119.9
P1—C2—H2A	108.9	C15—C16—H16	119.9
C1—C2—H2B	108.9	N1—C17—C11	111.65 (12)
P1—C2—H2B	108.9	N1—C17—C18	109.18 (13)
H2A—C2—H2B	107.7	C11—C17—C18	112.09 (14)
C17—N1—H1A	109.5	N1—C17—H17	107.9
C17—N1—H1B	109.5	C11—C17—H17	107.9
H1A—N1—H1B	109.5	C18—C17—H17	107.9
C17—N1—H1C	109.5	C17—C18—H18A	109.5
H1A—N1—H1C	109.5	C17—C18—H18B	109.5
H1B—N1—H1C	109.5	H18A—C18—H18B	109.5
C12—C11—C16	118.55 (18)	C17—C18—H18C	109.5
C12—C11—C17	119.59 (17)	H18A—C18—H18C	109.5
C16—C11—C17	121.69 (16)	H18B—C18—H18C	109.5
C11—C12—C13	120.7 (2)
O2—C1—C2—P1	−99.72 (16)	C13—C14—C15—C16	2.0 (3)
O1—C1—C2—P1	80.00 (16)	C12—C11—C16—C15	−0.7 (3)
O4—P1—C2—C1	−71.68 (13)	C17—C11—C16—C15	174.61 (16)
O3—P1—C2—C1	162.51 (11)	C14—C15—C16—C11	−1.0 (3)
O5—P1—C2—C1	43.93 (13)	C12—C11—C17—N1	−127.50 (16)
C16—C11—C12—C13	1.5 (3)	C16—C11—C17—N1	57.2 (2)
C17—C11—C12—C13	−173.91 (19)	C12—C11—C17—C18	109.65 (18)
C11—C12—C13—C14	−0.6 (3)	C16—C11—C17—C18	−65.7 (2)
C12—C13—C14—C15	−1.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O4^i	0.84	1.75	2.5781 (15)	169
O5—H5···O3^ii	0.84	1.75	2.5834 (15)	176
N1—H1A···O4	0.91	1.88	2.7603 (16)	164
N1—H1B···O3^i	0.91	1.95	2.8293 (16)	162
N1—H1C···O2^iii	0.91	2.04	2.9334 (17)	166
C2—H2B···Cg1^iv	0.99	2.75	3.6417 (19)	150

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