Issue contents
Download PDF of article
Download CIF
3D view
Navigation
Highlighting
Dictionary of Crystallography reference
IUPAC Gold Book reference
more ...
Download citation
FormatBIBTeX
EndNote
RefMan
Refer
Medline
CIF
SGML
Plain Text
share
Previous article
Next article
Previous article
Issue contents
Download PDF of article
Download CIF
3D view
Navigation
Highlighting
Dictionary of Crystallography reference
IUPAC Gold Book reference
more ...
Download citation
FormatBIBTeX
EndNote
RefMan
Refer
Medline
CIF
SGML
Plain Text
share
Next article

organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 67| Part 2| February 2011| Page o513
doi:10.1107/S1600536811001267

[1-(Carb­­oxy­meth­yl)cyclo­hex­yl]methanaminium nitrate

Elise J. C. de Vries,a* Caryn Gamblea and Ahmed Shaikjeea

aMolecular Science Institute, School of Chemistry, University of the Witwatersrand, PO WITS, 2050 Johannesburg, South Africa
*Correspondence e-mail: elise.devries@wits.ac.za

(Received 3 December 2010; accepted 10 January 2011; online 29 January 2011)

The title compound, C9H18NO2+·NO3−, is an anhydrous nitrate salt of gabapentin, which is formed serendipitously in the presence of selected non-coordinating metals. The crystal structure involves extensive hydrogen bonding between the –NH3+ and –COOH groups and the nitrate anion.

Related literature

For related structures, see: Ibers (2001[Ibers, J. A. (2001). Acta Cryst. C57, 641-643.]); Ananda et al. (2003[Ananda, K., Aravinda, S., Vasudev, P. G., Raja, K. M. P., Sivaramakrishnan, H., Nagarajan, K., Shamala, N. & Balaram, P. (2003). Curr. Sci. 85, 1002-1011.]); Reece & Levendis (2008[Reece, H. A. & Levendis, D. C. (2008). Acta Cryst. C64, o105-o108.]); Braga et al. (2008[Braga, D., Grepioni, F., Maini, L., Rubini, K., Polito, M., Brescello, R., Cotarca, L., Duarte, M. T., Andre, V. & Piedade, M. F. M. (2008). New J. Chem. 32, 1788-1795.]); Fabbiani et al. (2010[Fabbiani, F. P. A., Levendis, D. C., Buth, G., Kuhs, W. F., Shankland, N. & Sowa, H. (2010). CrystEngComm, 12, 2354-2360.]). For the role of γ-amino­butyric acid (GABA) as an inhibitory neurotransmitter, see: Bowery (1993[Bowery, N. G. (1993). Annu. Rev. Pharmacol. Toxicol. 33, 109-147.]). Gabapentin is used as a neuroleptic drug in the treatment of epilepsy (Taylor, 1993[Taylor, C. P. (1993). New Trends in Epilepsy Management, edited by D. Chadwick, pp. 13-40. London: Royal Society of Medicine Services.]) but its applications have been extended to the treatment of neuropathic pain (Magnus, 1999[Magnus, L. (1999). Epilepsia, 40, s66-s72.]).

[Scheme 1]

Experimental

Crystal data

  • C9H18NO2+·NO3−

  • Mr = 234.25

  • Orthorhombic, P 21 21 21

  • a = 8.1743 (8) Å

  • b = 11.5945 (11) Å

  • c = 12.0396 (9) Å

  • V = 1141.08 (18) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.11 mm−1

  • T = 173 K

  • 0.65 × 0.15 × 0.14 mm
Data collection

  • Bruker APEXII CCD diffractometer

  • 5654 measured reflections

  • 1448 independent reflections

  • 1278 reflections with I > 2σ(I)

  • Rint = 0.044
Refinement

  • R[F2 > 2σ(F2)] = 0.033

  • wR(F2) = 0.084

  • S = 1.06

  • 1448 reflections

  • 146 parameters

  • H-atom parameters constrained

  • Δρmax = 0.22 e Å−3

  • Δρmin = −0.14 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
N1—H1A⋯O5i 0.91 2.02 2.828 (2) 147
N1—H1A⋯O4i 0.91 2.41 3.215 (2) 147
N1—H1A⋯N2i 0.91 2.58 3.465 (3) 164
N1—H1B⋯O4ii 0.91 2.06 2.951 (3) 168
N1—H1B⋯O3ii 0.91 2.47 3.022 (2) 119
N1—H1B⋯N2ii 0.91 2.60 3.390 (3) 146
N1—H1C⋯O1 0.91 1.90 2.760 (2) 157
O2—H2C⋯O5 0.84 1.81 2.646 (2) 175
O2—H2C⋯N2 0.84 2.60 3.376 (2) 154
Symmetry codes: (i) [-x+{\script{3\over 2}}, -y, z-{\script{1\over 2}}]; (ii) [-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}].

Data collection: APEX2 (Bruker, 2005[Bruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-NT (Bruker, 2005[Bruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008)[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]; program(s) used to refine structure: SHELXL97 (Sheldrick, 2008)[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]; molecular graphics: X-SEED (Barbour, 2001[Barbour, L. J. (2001). J. Supramol. Chem. 1, 189-191.]; Atwood & Barbour, 2003[Atwood, J. L. & Barbour, L. J. (2003). Cryst. Growth Des. 3, 3-8.]); software used to prepare material for publication: X-SEED.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811001267/pb2049sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536811001267/pb2049Isup2.hkl

checkCIF report


Comment top

The role of γ-aminobutyric acid (GABA) as an inhibitory neurotransmitter (Bowery, 1993) has stimulated research on the synthesis of GABA analogues as potential central nervous system agents. One of these analogues is the amino acid gabapentin [1-(aminomethyl)cyclohexaneacetic acid] which is commercially available as Neurotin. Gabapentin is used as a neuroleptic drug in the treatment of epilepsy (Taylor, 1993) but its applications have been extended to the treatment of neuropathic pain (Magnus, 1999). Gabapentin is widely studied and already four polymorphic forms of the drug are known, three polymorphic forms under ambient conditions (Ibers, 2001; Reece and Levendis, 2008; Braga et al., 2008) and a fourth at high pressure (Fabbiani et al., 2010). The present paper reports on the formation of an anhydrous gabapentin nitrate salt, complex (I).

Complex (I) was obtained serendipitously when investigating the possibility of producing novel metal complexes with gabapentin. Lithium-, chromium-, indium-, iron- and aluminium nitrate were used in an attempt to make metal complexes. However analysis of the crystalline materials revealed a gabapentin nitrate salt was obtained in each case. The atomic numbering scheme of the gabapentin nitrate complex, C9H18NO2+.NO3-, is shown in Fig. 1. Complex (I) crystallizes in the orthorhombic space group P212121 with a protonated amine group. The cyclohexane ring is in the chair conformation with the ammonium group in the equatorial position. The conformation of the gabapentin molecule is defined by the formation of an intramolecular hydrogen bond between the carboxylate oxygen and one of the hydrogen atoms belonging to the ammonium group (N1—H1C···O1). The crystal packing shows how each nitrate anion links to three adjacent molecules by means of one O—H···O, four N—H···O, two N—H···N and one O—H···N hydrogen-bonding interactions. The donors are the H atoms of the carboxylic acid and amine group, while the acceptors include all three O atoms of the nitrate anion (Fig. 2). Additionally, one nitrate O atom is involved in a weak hydrogen bonding interaction with a symmetry related carbon atom, with a C9—H9B···O3 distance of 3.317 (3) Å and angle of 149°.

Related literature top

For related structures, see: Ibers (2001); Ananda et al. (2003); Reece & Levendis (2008); Braga et al. (2008); Fabbiani et al. (2010). For the role of γ-aminobutyric acid (GABA) as an inhibitory neurotransmitter, see: Bowery (1993). Gabapentin is used as a neuroleptic drug in the treatment of epilepsy (Taylor, 1993) but its applications have been extended to the treatment of neuropathic pain (Magnus, 1999).

Experimental top

Gabapentin was purchased from Sigma-Aldrich. The gabapentin nitrate salt is formed serendipitously by combining gabapentin with one of the following metal salts in 1:1 stoichiometric ratios; lithium-, chromium-, indium-, iron- and aluminium nitrate. The metal salt and gabapentin were dissolved in 0.1 molar nitric acid and allowed to undergo slow evaporation at ambient temperature. It was noted that this complex did not form if the metal salt was removed from the reaction.

Refinement top

All H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with C—H bond lengths of 0.99 (aromatic CH) 1.00 (methine CH), 0.99 (methylene CH2) and 0.98 Å (methyl CH3), and with Uiso(H) = 1.2 or 1.5 times Ueq(C). In the absence of significant anomalous scattering, Friedel equivalents were merged before the final refinement.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT-NT (Bruker, 2005); data reduction: SAINT-NT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001; Atwood & Barbour, 2003); software used to prepare material for publication: X-SEED (Barbour, 2001; Atwood & Barbour, 2003).

Figures top
[Figure 1] Fig. 1. The atomic numbering scheme of complex (I). Displacement ellipsoids are drawn at 50% probability level.
[Figure 2] Fig. 2. Projection of the unit cell of complex (I) down the a axis. All hydrogen atoms removed, except those involved in hydrogen bonding. Hydrogen bonds are indicated as dashed lines.
[1-(Carboxymethyl)cyclohexyl]methanaminium nitrate top
Crystal data top
C9H18NO2+·NO3−F(000) = 504
Mr = 234.25Dx = 1.364 Mg m−3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 1858 reflections
a = 8.1743 (8) Åθ = 3.0–25.8°
b = 11.5945 (11) ŵ = 0.11 mm−1
c = 12.0396 (9) ÅT = 173 K
V = 1141.08 (18) Å3Plate, colourless
Z = 40.65 × 0.15 × 0.14 mm
Data collection top
Bruker APEXII CCD
diffractometer		1278 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.044
Graphite monochromatorθmax = 27.0°, θmin = 2.4°
ϕ and ω scansh = −10→8
5654 measured reflectionsk = −12→14
1448 independent reflectionsl = −13→15
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.084H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0451P)2 + 0.0272P]
where P = (Fo2 + 2Fc2)/3
1448 reflections(Δ/σ)max < 0.001
146 parametersΔρmax = 0.22 e Å−3
0 restraintsΔρmin = −0.14 e Å−3
Crystal data top
C9H18NO2+·NO3−V = 1141.08 (18) Å3
Mr = 234.25Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 8.1743 (8) ŵ = 0.11 mm−1
b = 11.5945 (11) ÅT = 173 K
c = 12.0396 (9) Å0.65 × 0.15 × 0.14 mm
Data collection top
Bruker APEXII CCD
diffractometer		1278 reflections with I > 2σ(I)
5654 measured reflectionsRint = 0.044
1448 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0330 restraints
wR(F2) = 0.084H-atom parameters constrained
S = 1.06Δρmax = 0.22 e Å−3
1448 reflectionsΔρmin = −0.14 e Å−3
146 parameters
Special details top

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
xyzUiso*/Ueq
C10.5335 (2)0.08869 (17)0.35572 (15)0.0209 (4)
C20.3870 (2)0.03596 (17)0.41650 (16)0.0221 (4)
H2A0.42500.00310.48790.026*
H2B0.30760.09790.43370.026*
C30.3003 (3)−0.0580 (2)0.35067 (17)0.0301 (5)
H3B0.2046−0.08600.39320.036*
H3A0.3756−0.12380.33930.036*
C40.2437 (3)−0.0124 (2)0.23826 (18)0.0369 (6)
H4B0.15970.04800.24970.044*
H4A0.1931−0.07590.19530.044*
C50.3869 (3)0.0380 (2)0.17244 (17)0.0354 (6)
H5A0.4643−0.02460.15300.042*
H5B0.34560.07210.10250.042*
C60.4764 (3)0.13032 (18)0.23945 (16)0.0272 (5)
H6B0.40310.19750.24900.033*
H6A0.57320.15640.19680.033*
C70.5943 (3)0.19806 (17)0.41759 (16)0.0255 (5)
H7A0.69850.22300.38330.031*
H7B0.51360.26050.40550.031*
C80.6213 (3)0.18538 (18)0.54059 (17)0.0243 (5)
C90.6729 (3)0.0019 (2)0.33743 (16)0.0273 (5)
H9A0.6386−0.05380.27970.033*
H9B0.76940.04400.30860.033*
N10.7225 (2)−0.06315 (16)0.43807 (14)0.0290 (4)
H1A0.8126−0.10630.42260.043*
H1B0.6393−0.11030.45960.043*
H1C0.7460−0.01280.49380.043*
O10.7213 (2)0.12161 (14)0.58267 (12)0.0343 (4)
O20.5264 (2)0.25326 (14)0.59950 (11)0.0325 (4)
H2C0.54560.24340.66740.039*
N20.4911 (2)0.27445 (15)0.87814 (13)0.0245 (4)
O30.3960 (2)0.34667 (14)0.84059 (13)0.0397 (4)
O40.5086 (2)0.26085 (14)0.97989 (11)0.0351 (4)
O50.5740 (2)0.21168 (14)0.81312 (11)0.0333 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0231 (11)0.0206 (10)0.0191 (9)−0.0003 (8)0.0014 (8)0.0006 (7)
C20.0206 (10)0.0232 (10)0.0224 (9)0.0005 (9)0.0021 (8)0.0002 (8)
C30.0306 (12)0.0289 (12)0.0307 (11)−0.0083 (10)−0.0026 (10)0.0029 (9)
C40.0397 (14)0.0353 (13)0.0358 (13)−0.0083 (12)−0.0138 (10)−0.0028 (10)
C50.0492 (15)0.0355 (13)0.0215 (10)−0.0054 (12)−0.0070 (10)0.0010 (9)
C60.0330 (13)0.0274 (11)0.0212 (10)−0.0035 (10)−0.0009 (9)0.0051 (8)
C70.0265 (11)0.0211 (10)0.0288 (11)−0.0043 (9)−0.0007 (9)0.0025 (8)
C80.0220 (11)0.0213 (10)0.0297 (11)−0.0052 (9)−0.0004 (9)−0.0016 (8)
C90.0294 (11)0.0283 (12)0.0241 (10)0.0030 (10)0.0062 (9)0.0031 (9)
N10.0279 (10)0.0273 (10)0.0318 (10)0.0078 (8)0.0056 (8)0.0008 (8)
O10.0364 (10)0.0356 (9)0.0307 (8)0.0084 (8)−0.0063 (7)−0.0017 (7)
O20.0340 (9)0.0381 (9)0.0254 (7)0.0089 (8)−0.0028 (6)−0.0040 (6)
N20.0241 (10)0.0224 (9)0.0268 (9)−0.0001 (8)−0.0017 (7)0.0001 (7)
O30.0399 (10)0.0424 (10)0.0369 (9)0.0201 (9)−0.0004 (8)0.0076 (7)
O40.0458 (10)0.0381 (9)0.0214 (7)0.0065 (8)−0.0056 (7)−0.0010 (7)
O50.0353 (9)0.0357 (9)0.0288 (8)0.0143 (8)−0.0002 (7)−0.0053 (7)
Geometric parameters (Å, º) top
C1—C21.531 (3)C6—H6A0.9900
C1—C91.536 (3)C7—C81.504 (3)
C1—C71.552 (3)C7—H7A0.9900
C1—C61.552 (3)C7—H7B0.9900
C2—C31.522 (3)C8—O11.214 (3)
C2—H2A0.9900C8—O21.313 (3)
C2—H2B0.9900C9—N11.484 (3)
C3—C41.525 (3)C9—H9A0.9900
C3—H3B0.9900C9—H9B0.9900
C3—H3A0.9900N1—H1A0.9100
C4—C51.530 (3)N1—H1B0.9100
C4—H4B0.9900N1—H1C0.9100
C4—H4A0.9900O2—H2C0.8400
C5—C61.528 (3)N2—O31.229 (2)
C5—H5A0.9900N2—O41.243 (2)
C5—H5B0.9900N2—O51.266 (2)
C6—H6B0.9900
C2—C1—C9112.79 (16)C5—C6—H6B108.8
C2—C1—C7110.32 (16)C1—C6—H6B108.8
C9—C1—C7111.50 (17)C5—C6—H6A108.8
C2—C1—C6108.67 (17)C1—C6—H6A108.8
C9—C1—C6107.29 (16)H6B—C6—H6A107.7
C7—C1—C6105.95 (16)C8—C7—C1116.07 (16)
C3—C2—C1113.65 (16)C8—C7—H7A108.3
C3—C2—H2A108.8C1—C7—H7A108.3
C1—C2—H2A108.8C8—C7—H7B108.3
C3—C2—H2B108.8C1—C7—H7B108.3
C1—C2—H2B108.8H7A—C7—H7B107.4
H2A—C2—H2B107.7O1—C8—O2122.55 (19)
C2—C3—C4110.82 (19)O1—C8—C7124.7 (2)
C2—C3—H3B109.5O2—C8—C7112.73 (19)
C4—C3—H3B109.5N1—C9—C1114.76 (16)
C2—C3—H3A109.5N1—C9—H9A108.6
C4—C3—H3A109.5C1—C9—H9A108.6
H3B—C3—H3A108.1N1—C9—H9B108.6
C3—C4—C5111.1 (2)C1—C9—H9B108.6
C3—C4—H4B109.4H9A—C9—H9B107.6
C5—C4—H4B109.4C9—N1—H1A109.5
C3—C4—H4A109.4C9—N1—H1B109.5
C5—C4—H4A109.4H1A—N1—H1B109.5
H4B—C4—H4A108.0C9—N1—H1C109.5
C6—C5—C4111.14 (18)H1A—N1—H1C109.5
C6—C5—H5A109.4H1B—N1—H1C109.5
C4—C5—H5A109.4C8—O2—H2C109.5
C6—C5—H5B109.4O3—N2—O4121.46 (18)
C4—C5—H5B109.4O3—N2—O5120.20 (16)
H5A—C5—H5B108.0O4—N2—O5118.34 (18)
C5—C6—C1113.72 (17)
C9—C1—C2—C3−65.3 (2)C7—C1—C6—C5−170.79 (19)
C7—C1—C2—C3169.32 (17)C2—C1—C7—C849.5 (2)
C6—C1—C2—C353.6 (2)C9—C1—C7—C8−76.7 (2)
C1—C2—C3—C4−56.9 (3)C6—C1—C7—C8166.91 (19)
C2—C3—C4—C556.0 (3)C1—C7—C8—O163.3 (3)
C3—C4—C5—C6−54.9 (3)C1—C7—C8—O2−118.1 (2)
C4—C5—C6—C154.1 (3)C2—C1—C9—N1−49.7 (2)
C2—C1—C6—C5−52.2 (2)C7—C1—C9—N175.1 (2)
C9—C1—C6—C570.0 (2)C6—C1—C9—N1−169.31 (18)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O5i0.912.022.828 (2)147
N1—H1A···O4i0.912.413.215 (2)147
N1—H1A···N2i0.912.583.465 (3)164
N1—H1B···O4ii0.912.062.951 (3)168
N1—H1B···O3ii0.912.473.022 (2)119
N1—H1B···N2ii0.912.603.390 (3)146
N1—H1C···O10.911.902.760 (2)157
O2—H2C···O50.841.812.646 (2)175
O2—H2C···N20.842.603.376 (2)154
Symmetry codes: (i) −x+3/2, −y, z−1/2; (ii) −x+1, y−1/2, −z+3/2.

Experimental details

Crystal data
Chemical formulaC9H18NO2+·NO3−
Mr234.25
Crystal system, space groupOrthorhombic, P212121
Temperature (K)173
a, b, c (Å)8.1743 (8), 11.5945 (11), 12.0396 (9)
V (Å3)1141.08 (18)
Z4
Radiation typeMo Kα
µ (mm−1)0.11
Crystal size (mm)0.65 × 0.15 × 0.14
Data collection
DiffractometerBruker APEXII CCD
diffractometer
Absorption correction–
No. of measured, independent and
observed [I > 2σ(I)] reflections		5654, 1448, 1278
Rint0.044
(sin θ/λ)max (Å−1)0.639
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.084, 1.06
No. of reflections1448
No. of parameters146
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.22, −0.14

Computer programs: APEX2 (Bruker, 2005), SAINT-NT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), X-SEED (Barbour, 2001; Atwood & Barbour, 2003).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O5i0.912.022.828 (2)147
N1—H1A···O4i0.912.413.215 (2)147
N1—H1A···N2i0.912.583.465 (3)164
N1—H1B···O4ii0.912.062.951 (3)168
N1—H1B···O3ii0.912.473.022 (2)119
N1—H1B···N2ii0.912.603.390 (3)146
N1—H1C···O10.911.902.760 (2)157
O2—H2C···O50.841.812.646 (2)175
O2—H2C···N20.842.603.376 (2)154
Symmetry codes: (i) −x+3/2, −y, z−1/2; (ii) −x+1, y−1/2, −z+3/2.
 

Acknowledgements

The authors would like to thank the National Research Foundation of South Africa and the University of the Witwatersrand for financial support. EJCV would like to acknowledge Dr M. Fernandes for informative discussions and advice.

References

First citationAnanda, K., Aravinda, S., Vasudev, P. G., Raja, K. M. P., Sivaramakrishnan, H., Nagarajan, K., Shamala, N. & Balaram, P. (2003). Curr. Sci. 85, 1002–1011.  CAS Google Scholar
 First citationAtwood, J. L. & Barbour, L. J. (2003). Cryst. Growth Des. 3, 3–8.  Web of Science CrossRef CAS Google Scholar
 First citationBarbour, L. J. (2001). J. Supramol. Chem. 1, 189–191.  CrossRef CAS Google Scholar
 First citationBowery, N. G. (1993). Annu. Rev. Pharmacol. Toxicol. 33, 109–147.  CrossRef CAS PubMed Web of Science Google Scholar
 First citationBraga, D., Grepioni, F., Maini, L., Rubini, K., Polito, M., Brescello, R., Cotarca, L., Duarte, M. T., Andre, V. & Piedade, M. F. M. (2008). New J. Chem. 32, 1788–1795.  Web of Science CSD CrossRef CAS Google Scholar
 First citationBruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.  Google Scholar
 First citationFabbiani, F. P. A., Levendis, D. C., Buth, G., Kuhs, W. F., Shankland, N. & Sowa, H. (2010). CrystEngComm, 12, 2354–2360.  Web of Science CSD CrossRef CAS Google Scholar
 First citationIbers, J. A. (2001). Acta Cryst. C57, 641–643.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
 First citationMagnus, L. (1999). Epilepsia, 40, s66–s72.  Web of Science CrossRef PubMed CAS Google Scholar
 First citationReece, H. A. & Levendis, D. C. (2008). Acta Cryst. C64, o105–o108.  Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
 First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationTaylor, C. P. (1993). New Trends in Epilepsy Management, edited by D. Chadwick, pp. 13–40. London: Royal Society of Medicine Services.  Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 67| Part 2| February 2011| Page o513
doi:10.1107/S1600536811001267
Follow Acta Cryst. E
Sign up for e-alerts
E-alerts
Follow Acta Cryst. on Twitter
Twitter
Follow us on facebook
Facebook
Sign up for RSS feeds
RSS