A co-crystal of ethyl­enediammonium bis­(3,5-dinitro­benzoate) and 3,5-dinitro­benzoic acid

Jones, H.P.; Gillon, A.L.; Davey, R.J.

doi:10.1107/S1600536805015333

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 61| Part 6| June 2005| Pages o1823-o1825

https://doi.org/10.1107/S1600536805015333

A co-crystal of ethylenediammonium bis(3,5-dinitrobenzoate) and 3,5-dinitrobenzoic acid

Helen P. Jones,^a Amy L. Gillon ^a ‡ and Roger J. Davey ^a ^*

^aColloids, Crystals and Interfaces Group, School of Chemical Engineering and Analytical Sciences, The University of Manchester, PO Box 88, Manchester M60 1QD, England
^*Correspondence e-mail: h.jones-2@postgrad.manchester.ac.uk

(Received 6 April 2005; accepted 13 May 2005; online 21 May 2005)

The co-crystal of ethylenediammonium bis(3,5-dinitrobenzoate) and 3,5-dinitrobenzoic acid, namely ethylenediaminium–3,5-dinitrobenzoate–3,5-dinitrobenzoic acid (1/2/2), C₂H₁₀N₂²⁺·2C₇H₃N₂O₆⁻·2C₇H₄N₂O₆, has as the asymmetric unit one 3,5-dinitrobenzoic acid molecule, one 3,5-dinitrobenzoate ion and one-half of the ethylenediammonium ion, as this cation lies on an inversion centre. Each ethylenediammonium ion is hydrogen bonded to four benzoate ions and two benzoic acid molecules.

Comment

During experiments to measure the solubility of the monoclinic form of ethylenediammonium bis(3,5-dinitrobenzoate), cocrystals, (I), of this salt with 3,5-dinitrobenzoic acid were obtained.

To measure the solubility of ethylenediammonium bis(3,5-dinitrobenzoate) as a function of pH at 323 K, a suspension of the salt in water was prepared and allowed to equilibrate (Jones et al., 2005 ). In one experiment, the pH was found to be unusually low for a slurry of this salt and the experiment was stopped, but the sample continued to be held at 323 K. The cocrystals grew as pale-yellow prisms and were recovered on filtration of the slurry. Formation of these cocrystals was not observed in other solubility measurements at higher pH. Protonated 3,5-dinitrobenzoic acid is only expected to be present below pH 5 at 323 K (de Levie et al., 1999 ).

In the crystal structure, both a protonated and a deprotonated 3,5-dinitrobenzoic acid molecule are present in the asymmetric unit. The ethylenediammonium ion lies on an inversion centre so that only one-half of the ion is in the asymmetric unit. Fig. 1 shows the structure and atom labelling.

Each ethylenediammonium ion is hydrogen bonded to four benzoate ions and two benzoic acid molecules (Fig. 2). The crystal structure contains hydrogen-bonded chains of ethylenediammonium and benzoate ions along the a axis in the motif C₂²(6) (Fig. 3), hydrogen-bonded dimers of benzoate ions with benzoic acid molecules with an O—H⋯O hydrogen bond through atom H7 in the motif D₁¹(2), and dimers of ethylenediammonium ions hydrogen bonded to the carbonyl group of a benzoic acid molecule in the motif D₁¹(2). The benzoate ions in this structure all lie in one plane and the benzoic acid molecules all lie in another orientation.

Figure 1
View of the asymmetric unit of (I)

, including the whole ethylenediaminium ion, which is on an inversion centre. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code: (i) −x, −y, −z.]

Figure 2
Hydrogen bonding (dashed lines) between the ethylenediaminium and 3,5-dinitrobenzoate ions and the 3,5-dinitrobenzoic acid molecules.

Figure 3
Unit cell contents, viewed along the c axis, showing hydrogen-bonded chains (dashed lines) along the a axis.

Experimental

Monoclinic ethylenediaminium bis(3,5-dinitrobenzoate) was prepared by precipitation from a mixture of solutions of ethylenediamine (0.0145 mol) and 3,5-dinitrobenzoic acid (0.029 mol; supplied by Sigma–Aldrich, 99%) in ethanol (50 ml). An excess of monoclinic ethylenediammonium bis(3,5-dinitrobenzoate) (0.0145 mol) was suspended in water (40 ml) at 323 K with stirring. The solution pH was recorded as 3.79. After 20 h, stirring was stopped and the suspension was held at 323 K for 5 d. The suspension was filtered and pale-yellow prisms were observed in the powder of the monoclinic ethylenediammonium bis(3,5-dinitrobenzoate).

Crystal data

C₂H₁₀N₂²⁺·2C₇H₃N₂O6^-·2C₇H₄N₂O₆
M_r = 908.6
Triclinic, $[P \overline 1]$
a = 7.0452 (3) Å
b = 11.2345 (4) Å
c = 11.7627 (5) Å
α = 91.838 (2)°
β = 96.230 (2)°
γ = 98.710 (1)°
V = 913.72 (6) Å³
Z = 1
D_x = 1.651 Mg m⁻³
Mo Kα radiation
Cell parameters from 5294 reflections
θ = 1.0–25.0°
μ = 0.15 mm⁻¹
T = 293 (2) K
Prism, pale yellow
0.3 × 0.2 × 0.1 mm

Data collection

Nonius KappaCCD diffractometer
Thick-slice φ and ω scans to fill asymmetric unit
Absorption correction: multi-scan(Blessing, 1995 )T_min = 0.916, T_max = 0.986
8852 measured reflections
3241 independent reflections
2256 reflections with I > 2σ(I)
R_int = 0.046
θ_max = 25.2°
h = −8 → 8
k = −13 → 13
l = −14 → 12

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.046
wR(F²) = 0.136
S = 1.01
3241 reflections
294 parameters
H atoms treated by a mixture of independent and constrained refinement
w = 1/[σ²(F_o²) + (0.0776P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.21 e Å⁻³
Extinction correction: SHELXL97
Extinction coefficient: 0.016 (4)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O7—H7⋯O1	0.83 (1)	1.68 (1)	2.507 (2)	173 (4)
N5—H5A⋯O2	0.89	1.88	2.732 (3)	161
N5—H5B⋯O8ⁱⁱ	0.89	2.17	2.820 (3)	129
N5—H5C⋯O1ⁱⁱ	0.89	2.02	2.899 (3)	170
Symmetry code: (ii) x+1, y, z.

All H atoms attached to C and N atoms were fixed using a riding model, with C—H distances 0.93 Å (C_ArH) and 0.97 Å (CH₂), and N—H distances 0.89 Å. The U_iso(H) values were set equal to 1.2U_eq of the carrier atom for these H atoms. The hydroxy H atom was located in a Fourier difference map and the coordinates were refined with the O—H bond distance restrained to 0.82 (1) Å.

Data collection: COLLECT (Nonius, 2000 ); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997 ); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536805015333/ng6162sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536805015333/ng6162Isup2.hkl

Computing details top

Data collection: Collect (Nonius, 2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

ethylenediaminium–3,5-dinitrobenzoate–3,5-dinitrobenzoic acid (1/2/2), C₂H₁₀N₂²⁺·2C₇H₃N₂O₆^-·2C₇H₄N₂O₆ top

Crystal data top

0.5C₂H₁₀N₂²⁺·C₇H₃N₂O₆⁻·C₇H₄N₂O₆	Z = 2
M_r = 454.3	F(000) = 466
Triclinic, P1	D_x = 1.651 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.0452 (3) Å	Cell parameters from 5294 reflections
b = 11.2345 (4) Å	θ = 1.0–25.0°
c = 11.7627 (5) Å	µ = 0.15 mm⁻¹
α = 91.838 (2)°	T = 293 K
β = 96.230 (2)°	Prism, pale yellow
γ = 98.710 (1)°	0.3 × 0.2 × 0.1 mm
V = 913.72 (6) Å³

Data collection top

Nonius KappaCCD diffractometer	3241 independent reflections
Radiation source: Enraf–Nonius FR590	2256 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.046
φ or ω scans?	θ_max = 25.2°, θ_min = 2.5°
Absorption correction: multi-scan (Blessing, 1995)	h = −8→8
T_min = 0.916, T_max = 0.986	k = −13→13
8852 measured reflections	l = −14→12

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.046	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.136	w = 1/[σ²(F_o²) + (0.0776P)²] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
3241 reflections	Δρ_max = 0.20 e Å⁻³
294 parameters	Δρ_min = −0.21 e Å⁻³
1 restraint	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.016 (4)

Special details top

Experimental. Solution pH was measured using an Accumet Basic AB15 pH meter with an Accumet glass calomel pH electrode and an ATC probe to compensate for temperature changes.

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 (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.3739 (2)	0.04198 (13)	0.75723 (14)	0.0508 (4)
O2	0.6632 (3)	−0.01493 (13)	0.76044 (15)	0.0553 (5)
O3	0.7755 (3)	−0.38263 (14)	0.94862 (14)	0.0596 (5)
O4	0.6306 (3)	−0.42815 (15)	1.09778 (14)	0.0648 (5)
O5	0.0621 (3)	−0.26099 (18)	1.15926 (16)	0.0718 (6)
O6	−0.0276 (3)	−0.12294 (18)	1.05344 (18)	0.0724 (6)
O7	0.5246 (3)	0.24130 (15)	0.69250 (16)	0.0590 (5)
O8	0.2299 (3)	0.26663 (15)	0.62078 (17)	0.0680 (5)
O9	0.1253 (3)	0.66997 (17)	0.50938 (18)	0.0741 (6)
O10	0.3350 (3)	0.82267 (16)	0.5700 (2)	0.0889 (7)
O11	0.9653 (3)	0.76827 (14)	0.73491 (15)	0.0618 (5)
O12	1.0348 (3)	0.58912 (16)	0.75615 (16)	0.0638 (5)
N1	0.6524 (3)	−0.37047 (16)	1.01241 (16)	0.0475 (5)
N2	0.0813 (3)	−0.19415 (18)	1.07990 (18)	0.0520 (5)
N3	0.2801 (3)	0.71433 (18)	0.55839 (17)	0.0537 (5)
N4	0.9221 (3)	0.65764 (17)	0.72899 (16)	0.0455 (5)
N5	0.9846 (3)	0.05043 (17)	0.65242 (17)	0.0571 (6)
H5A	0.8995	0.0265	0.7009	0.069*
H5B	0.9863	0.1285	0.6413	0.069*
H5C	1.1016	0.0382	0.6816	0.069*
C1	0.4465 (3)	−0.11491 (17)	0.87777 (17)	0.0371 (5)
C2	0.5689 (3)	−0.19825 (17)	0.90467 (17)	0.0394 (5)
H2	0.681	−0.1975	0.8694	0.047*
C3	0.5229 (3)	−0.28228 (18)	0.98423 (17)	0.0403 (5)
C4	0.3618 (3)	−0.28528 (19)	1.04054 (18)	0.0433 (6)
H4	0.332	−0.3427	1.0937	0.052*
C5	0.2463 (3)	−0.19926 (18)	1.01452 (17)	0.0400 (5)
C6	0.2833 (3)	−0.11494 (18)	0.93258 (18)	0.0395 (5)
H6	0.1998	−0.0598	0.9151	0.047*
C7	0.5006 (3)	−0.02253 (17)	0.79096 (18)	0.0403 (5)
C8	0.4724 (3)	0.43735 (17)	0.65036 (16)	0.0368 (5)
C9	0.3459 (3)	0.51274 (18)	0.60851 (17)	0.0391 (5)
H9	0.2179	0.482	0.5824	0.047*
C10	0.4134 (3)	0.63433 (18)	0.60626 (17)	0.0404 (5)
C11	0.5990 (3)	0.68435 (18)	0.64562 (17)	0.0400 (5)
H11	0.6405	0.7669	0.6452	0.048*
C12	0.7218 (3)	0.60689 (18)	0.68589 (17)	0.0375 (5)
C13	0.6631 (3)	0.48361 (18)	0.68852 (17)	0.0382 (5)
H13	0.7496	0.4332	0.7152	0.046*
C14	0.3964 (4)	0.30531 (19)	0.65396 (18)	0.0432 (6)
C15	0.9287 (3)	−0.01948 (18)	0.54167 (18)	0.0421 (5)
H15A	0.8006	−0.007	0.5102	0.051*
H15B	0.9249	−0.1048	0.5538	0.051*
H7	0.469 (5)	0.1743 (18)	0.709 (3)	0.123 (14)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0486 (11)	0.0417 (8)	0.0650 (10)	0.0101 (8)	0.0127 (8)	0.0141 (7)
O2	0.0492 (11)	0.0509 (9)	0.0700 (11)	0.0061 (8)	0.0237 (9)	0.0159 (8)
O3	0.0678 (13)	0.0629 (11)	0.0573 (11)	0.0291 (9)	0.0207 (10)	0.0089 (8)
O4	0.0793 (14)	0.0686 (11)	0.0535 (11)	0.0243 (10)	0.0148 (9)	0.0255 (8)
O5	0.0613 (13)	0.0999 (14)	0.0587 (12)	0.0094 (10)	0.0249 (10)	0.0247 (10)
O6	0.0568 (13)	0.0806 (13)	0.0898 (15)	0.0248 (10)	0.0301 (11)	0.0154 (10)
O7	0.0558 (12)	0.0416 (9)	0.0771 (12)	0.0025 (8)	0.0011 (9)	0.0145 (8)
O8	0.0566 (13)	0.0474 (9)	0.0902 (14)	−0.0091 (9)	−0.0146 (10)	0.0145 (8)
O9	0.0581 (13)	0.0767 (13)	0.0840 (14)	0.0186 (10)	−0.0189 (11)	0.0052 (10)
O10	0.0967 (18)	0.0460 (12)	0.1208 (19)	0.0235 (11)	−0.0197 (14)	0.0052 (10)
O11	0.0587 (12)	0.0467 (10)	0.0724 (12)	−0.0097 (8)	−0.0015 (9)	0.0027 (8)
O12	0.0422 (11)	0.0674 (11)	0.0818 (13)	0.0111 (9)	0.0032 (9)	0.0066 (9)
N1	0.0557 (14)	0.0459 (11)	0.0427 (11)	0.0130 (9)	0.0059 (10)	0.0060 (8)
N2	0.0418 (13)	0.0608 (13)	0.0524 (13)	0.0015 (10)	0.0105 (10)	0.0023 (10)
N3	0.0579 (15)	0.0534 (13)	0.0521 (12)	0.0192 (11)	0.0023 (11)	0.0025 (9)
N4	0.0413 (12)	0.0497 (12)	0.0449 (11)	0.0020 (10)	0.0083 (9)	0.0036 (8)
N5	0.0560 (14)	0.0594 (12)	0.0518 (12)	−0.0124 (10)	0.0190 (10)	−0.0014 (9)
C1	0.0410 (13)	0.0337 (10)	0.0355 (11)	0.0020 (9)	0.0051 (9)	−0.0013 (8)
C2	0.0416 (14)	0.0407 (11)	0.0364 (12)	0.0055 (10)	0.0084 (10)	−0.0011 (9)
C3	0.0445 (14)	0.0409 (11)	0.0361 (12)	0.0086 (10)	0.0046 (10)	0.0020 (9)
C4	0.0466 (15)	0.0454 (12)	0.0368 (12)	0.0013 (10)	0.0072 (10)	0.0036 (9)
C5	0.0350 (13)	0.0474 (12)	0.0369 (12)	0.0012 (10)	0.0093 (10)	−0.0024 (9)
C6	0.0379 (13)	0.0394 (11)	0.0407 (12)	0.0051 (9)	0.0040 (10)	−0.0014 (8)
C7	0.0431 (15)	0.0329 (11)	0.0438 (13)	−0.0003 (10)	0.0092 (11)	−0.0014 (9)
C8	0.0415 (14)	0.0384 (11)	0.0298 (11)	0.0020 (9)	0.0066 (9)	0.0032 (8)
C9	0.0379 (13)	0.0452 (12)	0.0328 (11)	0.0020 (10)	0.0041 (9)	−0.0004 (8)
C10	0.0472 (14)	0.0430 (12)	0.0327 (11)	0.0117 (10)	0.0055 (10)	0.0020 (8)
C11	0.0482 (15)	0.0356 (11)	0.0361 (12)	0.0048 (10)	0.0069 (10)	0.0015 (8)
C12	0.0387 (13)	0.0415 (11)	0.0316 (11)	0.0011 (9)	0.0077 (9)	0.0020 (8)
C13	0.0444 (14)	0.0393 (11)	0.0320 (11)	0.0069 (10)	0.0075 (10)	0.0039 (8)
C14	0.0467 (16)	0.0424 (12)	0.0385 (12)	0.0002 (11)	0.0041 (11)	0.0059 (9)
C15	0.0437 (14)	0.0389 (11)	0.0434 (12)	0.0004 (10)	0.0103 (10)	0.0060 (9)

Geometric parameters (Å, º) top

O1—C7	1.271 (3)	C1—C2	1.388 (3)
O2—C7	1.229 (3)	C1—C7	1.516 (3)
O3—N1	1.226 (2)	C2—C3	1.379 (3)
O4—N1	1.224 (2)	C2—H2	0.93
O5—N2	1.223 (3)	C3—C4	1.371 (3)
O6—N2	1.215 (3)	C4—C5	1.376 (3)
O7—C14	1.292 (3)	C4—H4	0.93
O7—H7	0.833 (10)	C5—C6	1.390 (3)
O8—C14	1.205 (3)	C6—H6	0.93
O9—N3	1.204 (3)	C8—C9	1.384 (3)
O10—N3	1.219 (3)	C8—C13	1.386 (3)
O11—N4	1.232 (2)	C8—C14	1.502 (3)
O12—N4	1.213 (2)	C9—C10	1.379 (3)
N1—C3	1.468 (3)	C9—H9	0.93
N2—C5	1.469 (3)	C10—C11	1.367 (3)
N3—C10	1.477 (3)	C11—C12	1.377 (3)
N4—C12	1.468 (3)	C11—H11	0.93
N5—C15	1.483 (3)	C12—C13	1.386 (3)
N5—H5A	0.89	C13—H13	0.93
N5—H5B	0.89	C15—C15ⁱ	1.506 (4)
N5—H5C	0.89	C15—H15A	0.97
C1—C6	1.377 (3)	C15—H15B	0.97

C14—O7—H7	109 (3)	C1—C6—C5	118.5 (2)
O4—N1—O3	123.8 (2)	C1—C6—H6	120.7
O4—N1—C3	118.1 (2)	C5—C6—H6	120.7
O3—N1—C3	118.10 (18)	O2—C7—O1	125.5 (2)
O6—N2—O5	123.3 (2)	O2—C7—C1	117.6 (2)
O6—N2—C5	118.5 (2)	O1—C7—C1	116.8 (2)
O5—N2—C5	118.1 (2)	C9—C8—C13	120.38 (19)
O9—N3—O10	123.6 (2)	C9—C8—C14	118.1 (2)
O9—N3—C10	118.95 (19)	C13—C8—C14	121.48 (19)
O10—N3—C10	117.5 (2)	C10—C9—C8	118.6 (2)
O12—N4—O11	124.0 (2)	C10—C9—H9	120.7
O12—N4—C12	118.64 (18)	C8—C9—H9	120.7
O11—N4—C12	117.41 (19)	C11—C10—C9	123.0 (2)
C15—N5—H5A	109.5	C11—C10—N3	118.33 (19)
C15—N5—H5B	109.5	C9—C10—N3	118.7 (2)
H5A—N5—H5B	109.5	C10—C11—C12	116.98 (19)
C15—N5—H5C	109.5	C10—C11—H11	121.5
H5A—N5—H5C	109.5	C12—C11—H11	121.5
H5B—N5—H5C	109.5	C11—C12—C13	122.6 (2)
C6—C1—C2	119.86 (19)	C11—C12—N4	118.40 (18)
C6—C1—C7	121.5 (2)	C13—C12—N4	119.0 (2)
C2—C1—C7	118.6 (2)	C8—C13—C12	118.3 (2)
C3—C2—C1	119.4 (2)	C8—C13—H13	120.8
C3—C2—H2	120.3	C12—C13—H13	120.8
C1—C2—H2	120.3	O8—C14—O7	125.3 (2)
C4—C3—C2	122.5 (2)	O8—C14—C8	120.6 (2)
C4—C3—N1	118.23 (19)	O7—C14—C8	114.1 (2)
C2—C3—N1	119.3 (2)	N5—C15—C15ⁱ	110.4 (2)
C3—C4—C5	116.8 (2)	N5—C15—H15A	109.6
C3—C4—H4	121.6	C15ⁱ—C15—H15A	109.6
C5—C4—H4	121.6	N5—C15—H15B	109.6
C4—C5—C6	122.9 (2)	C15ⁱ—C15—H15B	109.6
C4—C5—N2	118.01 (19)	H15A—C15—H15B	108.1
C6—C5—N2	119.0 (2)

Symmetry code: (i) −x+2, −y, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O7—H7···O1	0.83 (1)	1.68 (1)	2.507 (2)	173 (4)
N5—H5A···O2	0.89	1.88	2.732 (3)	161
N5—H5B···O8ⁱⁱ	0.89	2.17	2.820 (3)	129
N5—H5C···O1ⁱⁱ	0.89	2.02	2.899 (3)	170

Symmetry code: (ii) x+1, y, z.

Footnotes

‡Current address: Pharmaceutical R&D, Pfizer Global R&D (IPC 435), Ramsgate Road, Sandwich, Kent CT13 9NJ, England.

Acknowledgements

The authors thank Sanofi–Aventis Ltd for funding.

References

Blessing, R. H. (1995). Acta Cryst. A51, 33–38. CrossRef CAS Web of Science IUCr Journals Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Jones, H. P., Davey, R. J. & Cox, B. G. (2005). J. Phys. Chem. B, 109, 5273–5278. Web of Science CSD CrossRef PubMed CAS Google Scholar
Levie, R. de (1999). Aqueous Acid–Base Equilibria and Titrations. New York: Oxford University Press. Google Scholar
Nonius (2000). COLLECT. Nonius BV, Delft, The Netherlands. Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany. Google Scholar

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