research papers\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206

Accurate molecular structures and hydrogen bonding in two polymorphs of ortho-acetamidobenzamide by single-crystal neutron diffraction

aISIS Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, England, bDepartment of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, England, and cWestCHEM, Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland
*Correspondence e-mail: c.k.leech@rl.ac.uk

(Received 19 May 2006; accepted 4 July 2006)

The structures of both known forms of the polymorphic material ortho-acetamidobenzamide, C9H10N2O2, have been determined by low-temperature neutron single-crystal diffraction. Neutron diffraction allows the full description of the H-atom positions in this molecular material, which is vital in benchmarking related crystal-structure predictions. Significant conformational differences are indicated by a number of the torsion angles involving H atoms when compared with previous X-ray studies. A comprehensive description of the hydrogen-bonding scheme in both polymorphs is given.

1. Introduction

Computational methods of crystal-structure prediction for flexible molecules can only be successful if they can accurately model the energy changes involved in conformational polymorphism (Nowell & Price, 2005[Nowell, H. & Price, S. L. (2005). Acta Cryst. B61, 558-568.]; Bernstein, 2002[Bernstein, J. (2002). Polymorphism in Molecular Crystals. Oxford: Clarendon Press.]). A molecule can change its conformation, giving rise to an intramolecular energy penalty, if it thereby improves its interactions with other molecules such that the lower intermolecular lattice energy more than compensates for the increase due to the conformational change. The balance of these interactions is very sensitive to the positions of the protons involved in hydrogen-bonding interactions, and computationally optimizing the geometries of amide groups can have a marked effect on the calculated relative stability of crystal structures (Karamertzanis & Price, 2006[Karamertzanis, P. G. & Price, S. L. (2006). J. Chem. Theory Comput. 2, 1184-1199.]). The two polymorphs of ortho-acetamidobenzamide (I) provide a particularly stringent test (Buttar et al., 1998[Buttar, D., Charlton, M. H., Docherty, R. & Starbuck. J. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 763-772.]) of whether computational methods can model the balance between intermolecular and intramolecular forces sufficiently adequately to allow realistic crystal-structure prediction studies.

[Scheme 1]

The α-form of the title compound (I) exhibits an intramolecular hydrogen bond between the O atom of the amide group and the N—H of the acetamido group, whereas the β form has a more twisted geometry and no intramolecular hydrogen bond (Errede et al., 1981[Errede, L. A., Etter, M. C., Williams, R. C. & Darnauer. S. M. (1981). J. Chem. Soc. Perkin Trans. 2, pp. 233-238.]; Etter, 1983[Etter, M. C. (1983). Mol. Cryst. Liq. Cryst. 93, 95-100.]). The total energy difference between the two forms has been calculated as ca 20 kJ mol−1 (Buttar et al., 1998[Buttar, D., Charlton, M. H., Docherty, R. & Starbuck. J. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 763-772.]; Day, 2002[Day, G. M. (2002). PhD thesis. University College London.]) and is considerably larger than expected for polymorphs of the same compound (ca 4 kJ mol−1: Bernstein, 2002[Bernstein, J. (2002). Polymorphism in Molecular Crystals. Oxford: Clarendon Press.]). Thus, the structure of the less stable β form would be rejected if generated during a crystal-structure prediction study (Buttar et al., 1998[Buttar, D., Charlton, M. H., Docherty, R. & Starbuck. J. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 763-772.]). The exact energy difference, defined as the difference between the conformational energies plus the difference between the intermolecular lattice energies, is highly dependent on:

  • (a) the particular ab initio or semi-empirical method used to calculate the conformational energies, with high-level correlated methods differing in the estimated intramolecular energy penalty by over 20 kJ mol−1 (Mourik et al., 2006[Mourik, T. van, Karamertzanis, P. G. & Price, S. L. (2006). J. Phys. Chem. A, 110, 8-12.]) and

  • (b) the molecular models used in calculating the conformational energies (Buttar et al., 1998[Buttar, D., Charlton, M. H., Docherty, R. & Starbuck. J. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 763-772.]; Day, 2002[Day, G. M. (2002). PhD thesis. University College London.]).

In previous studies, these conformational energies have been derived from the published single-crystal X-ray coordinates obtained by Errede et al. (1981[Errede, L. A., Etter, M. C., Williams, R. C. & Darnauer. S. M. (1981). J. Chem. Soc. Perkin Trans. 2, pp. 233-238.]) for the α and β forms, but both Buttar et al. and Day emphasize the influence that small deviations from expected bond lengths and angles (especially those involving H atoms) can have on the calculated energies. `Standardization' of C—H and N—H bond lengths to 1.08 and 1.01 Å, respectively, while effective in correcting errors in X-ray determined H-atom positions, does not alter errors in bond angles and bond torsions, nor does it address the possibility of the geometry of the NH2 group being affected by crystal packing (Day, 2002[Day, G. M. (2002). PhD thesis. University College London.]). Thus, accurate determinations of the full molecular structures of (I) in its two polymorphs are essential for the development of methods for calculating the relative stability of conformational polymorphs that differ so markedly in their hydrogen-bonding motifs. This work sets out to provide such accurate starting models for the α and β forms of (I) by employing single-crystal neutron diffraction (where the atomic positions of H atoms, as defined by the position of the nucleus of the atom, are typically obtained with greater accuracy and precision than from corresponding X-ray experiments) at a time-of-flight neutron source.

2. Experimental

ortho-Acetamidobenzamide (C9H10N2O2) was prepared according to the literature method of Baker & Almaula (1962[Baker, B. R. & Almaula, P. I. (1962). J. Org. Chem. 27, 4672-4674.]). All starting chemicals were purchased from the Aldrich Chemical Company and were used without further purification. The yield was 82% and microanalysis showed excellent agreement between found (C 61.0, H 5.7, N 15.7) and calculated (C 60.7, H 5.7, N 15.7) percentages. X-ray powder diffraction confirmed the product to be the α form.

Crystals of the α form, suitable for single-crystal neutron diffraction, were obtained relatively easily by slow evaporation from a dilute solution of (I) in methanol. The single crystals of the β form of (I) were produced in the same way, but only after some partially deuterated polycrystalline acetamidobenzamide (shown to be the β form by X-ray powder diffraction) had been prepared in the laboratory.

Neutron diffraction data were collected from crystals of the β form (dimensions 3.5 × 1.5 × 1.0 mm3) and the α form (dimensions 5.0 × 2.0 × 1.0 mm3); each crystal was mounted on a closed-cycle refrigerator on a vertically mounted ω-orienter. Data were collected on the SXD instrument (Wilson, 1990[Wilson, C. C. (1990). IOP Conf. Ser. 107, 145.]; Keen & Wilson, 1996[Keen, D. A. & Wilson, C. C. (1996). Report RAL-TR-96-083. Rutherford Appleton Laboratory, Oxfordshire, England.]; Keen et al., 2006[Keen, D. A., Gutmann, M. J. & Wilson, C. C. (2006). J. Appl. Cryst. 39, 714-722.]) at the ISIS spallation neutron source, using the time-of-flight Laue diffraction method. This method uses a wavelength-sorted white neutron beam, along with 11 large area position-sensitive detectors, to allow a large volume of reciprocal space to be measured in a single-crystal setting (a `frame'). The full data collection comprises a series of such frames, each collected with a stationary crystal-detector arrangement.

For both crystals the temperature was held at 30 ± 5 K throughout the experiment. A total of six frames, each containing information from 11 detectors, was collected, with a typical exposure time of 8 h (1300 μA h) for each frame for the β form crystal and 4 h (700 μA h) for each frame for the α-form crystal. The difference in exposure time required was a result of the difference in crystal size and diffraction quality.

Reflection intensities were extracted and reduced to structure factors using standard SXD procedures, as implemented in the computer program SXD2001 (Gutmann, 2005[Gutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.]). A total of 11 488 reflections were collected for the β form and 5267 reflections for the α form. Crystal data and refinement details are given in Table 1[link].1 Refinements were carried out using SHELXL97 (Sheldrick, 1997a[Sheldrick, G. M. (1997a). SHELXL97. University of Göttingen, Germany.]) using anisotropic displacement parameters for all atoms, including the H atoms. The resulting molecular structures are shown in Fig. 1[link], with the bond lengths involving H atoms detailed in Table 2[link].

Table 1
Crystal data and refinement details for (I)

  α form β form
Crystal data
Chemical formula C9H10N2O2 C9H10N2O2
Mr 178.19 178.19
Cell setting, space group Monoclinic, P21/n Monoclinic, P21/c
Temperature (K) 30 (2) 30 (2)
a, b, c (Å) 4.8591 (12), 14.395 (3), 12.250 (3) 7.788 (1), 8.972 (2), 12.547 (2)
β (°) 92.151 (16) 101.12 (1)
V3) 856.3 (3) 860.2 (3)
Z 4 4
Dx (Mg m−3) 1.382 1.376
Radiation type Neutron Neutron
Crystal form, colour Block, colourless Block, colourless
Crystal size (mm) 5.0 × 2.0 × 1.0 3.5 × 1.5 × 1.5
     
Data collection
Diffractometer SXD SXD
Data collection method Time-of-flight LAUE diffraction Time-of-flight LAUE diffraction
Absorption correction None Gaussian
No. of measured, independent and observed reflections 5267, 5267, 5267 11 484, 11 484, 11 484
Criterion for observed reflections I > 2σ(I) I > 2σ(I)
Rint 0.000 0.000
θmax (°) 81.7 82.5
     
Refinement
Refinement on F2 F2
R[F2 > 2σ(F2)], wR(F2), S 0.057, 0.128, 1.04 0.058, 0.148, 1.03
No. of reflections 5267 11 484
No. of parameters 274 274
H-atom treatment Refined independently Refined independently
Weighting scheme w = 1/[σ2(Fo2) + (0.0826P)2], where P = (Fo2 + 2Fc2)/3 w = 1/[σ2(Fo2) + (0.0926P)2 + 11.2116P], where P = (Fo2 + 2Fc2)/3
(Δ/σ)max <0.0001 <0.0001
Δρmax, Δρmin (fm Å–3) 2.003, −1.487 2.346, −2.384
Extinction method SHELXL SHELXL
Extinction coefficient 0.00129 (6) 0.0450 (7)
Computer programs used: SXD2001 (Gutmann, 2005[Gutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.]), SHELXS97 (Sheldrick, 1990[Sheldrick, G. M. (1990). Acta Cryst. A46, 467-473.]), SHELXL97 (Sheldrick, 1997a[Sheldrick, G. M. (1997a). SHELXL97. University of Göttingen, Germany.]), SHELXTL (Sheldrick, 1997b[Sheldrick, G. M. (1997b). SHELXTL, Version 5.03. Bruker AXS Inc., Madison, Wisconsin, USA.]).

Table 2
Comparison of bond lengths (Å) involving H atoms in (I)

  α form β form
X—H X-ray (room temperature) Neutron (30 K) X-ray (room temperature) Neutron (30 K)
N1—H1B 0.764 1.015 (3) 0.855 1.025 (2)
N1—H1A 0.946 1.026 (4) 0.997 1.025 (2)
N2—H2 0.819 1.025 (3) 0.836 1.020 (2)
C3—H3 0.928 1.088 (3) 0.898 1.090 (2)
C4—H4 0.959 1.092 (5) 0.958 1.086 (2)
C5—H5 0.883 1.099 (4) 0.832 1.090 (2)
C6—H6 1.189 1.082 (3) 0.944 1.086 (2)
C9—H9A 0.790 1.076 (5) 0.936 1.088 (2)
C9—H9B 0.899 1.078 (4) 0.980 1.090 (3)
C9—H9C 0.968 1.087 (4) 0.912 1.087 (3)
[Figure 1]
Figure 1
The molecular structure of (a) the α form of (I) at 30 K and (b) the β form of (I) at 30 K. All displacement ellipsoids are drawn at the 50% level.

3. Results and discussion

Unsurprisingly, with respect to the non-H atoms, the molecular and crystal structures obtained show good agreement with previously published X-ray structures. The r.m.s. difference between the non-H atoms of the neutron derived structure (30 K) and the corresponding non-H atoms of the published X-ray structures (room temperature) was 0.027 Å for α-AABA and 0.030 Å for β-AABA. Equally unsurprisingly, the differences with respect to the H atoms are substantial and these are summarized in Tables 2[link] and 3[link]. In Table 2[link] those bond lengths and angles involving H atoms are compared for the models derived from the neutron data and the published X-ray structures. Differences in bond lengths are as expected, with the X-ray distances being systematically shorter than their neutron counterparts. For the NH2 groups, the X-ray structures give H atoms in the correct general locations, but there are significant differences in the angles. The pyramidalization of the NH2 groups in the neutron structures (as defined by the distance d of the nitrogen N1 from the C7—H1A—H1B plane) is almost identical to that found in the X-ray structures: dneutron = +0.113 (3) Å, dX-ray = +0.112 Å for the α form; dneutron = + 0.060 (1) Å, dX-ray = + 0.041 Å for the β form.

Table 3
Comparison of bond angles (°) involving H-atoms in (I)

  α form β form
XY—H X-ray (room temperature) Neutron (30 K) X-ray (room temperature) Neutron (30 K)
C7—N1—H1A 118 120.6 (2) 124 119.1 (1)
C7—N1—H1B 116 117.6 (2) 121 119.8 (1)
H1A—N1—H1B 122 118.8 (3) 114 120.3 (2)
C1—N2—H2 110 112.3 (2) 115 119.1 (1)
C8—N2—H2 120 118.1 (2) 122 118.7 (1)
C2—C3—H3 114 119.2 (3) 118 119.7 (1)
C3—C4—H4 122 119.5 (3) 122 120.7 (1)
C5—C4—H4 119 121.4 (3) 119 119.3 (1)
C4—C3—H3 125 119.5 (3) 120 119.9 (1)
C4—C5—H5 125 120.5 (3) 120 120.0 (1)
C6—C5—H5 112 118.3 (2) 119 120.2 (1)
C1—C6—H6 130 119.4 (3) 118 119.0 (1)
C5—C6—H6 108 120.7 (3) 123 120.6 (1)
C8—C9—H9A 109 108.5 (3) 111 109.0 (1)
C8—C9—H9B 114 109.6 (4) 105 108.9 (1)
C8—C9—H9C 110 111.7 (3) 116 112.9 (2)
H9A—C9—H9B 96 107.2 (4) 95 107.9 (3)
H9A—C9—H9C 106 111.2 (5) 121 109.3 (2)
H9B—C9—H9C 120 108.6 (3) 103 108.7 (2)

The intermolecular interactions present in the two polymorphic forms are summarized in Figs. 2[link](a) and (b) and in Table 4[link]. Both forms exhibit the same number of short hydrogen bonds, those interactions occurring between the same chemical groups in each polymorph. These short hydrogen bonds are numbered 1–3 in the diagrams and tables. The main difference in the hydrogen-bonding patterns of the two polymorphs is that the O1⋯H2—N2 hydrogen bond (1) is intra-molecular in the α form and inter-molecular in the β form. In terms of graph-set notation (Etter, 1990[Etter, M. C. (1990). Acc. Chem. Res. 23, 120-126.]), the hydrogen bond 1 has the motif S(6) in the α form and C(6) in the β form, with the same six atoms being involved in each polymorph. Both forms exhibit the same dimer (hydrogen bond 2 O1⋯H1B—N1) and C(8) chain (hydrogen bond 3 O2⋯H1A—N1) motifs that link the molecules into sheets. However, as can be seen from Figs. 2[link](a) and (b), the appearance of these sheets is very different. In the α form the molecules lie approximately planar within the sheet and the dimers are arranged in a herringbone arrangement with adjacent dimers linked by hydrogen bond 3. In the β form, the plane of the molecules lies approximately normal to the plane of the sheet, and hydrogen bonds 1 and 3 are involved in linking adjacent dimers. In addition to the hydrogen bonds discussed above, there are a further two long hydrogen bonds (4 and 5) that occur only in the β form of (I).

Table 4
Hydrogen bonds in (I)

Hydrogen bond Label Form O⋯H O⋯N O—H—N Symmetry relation Graph set
O1⋯H2—N2 1 α 1.771 (3) 2.649 (2) 141.2 (3) O1i⋯H2i—N2i S(6)
    β 2.024 (2) 3.032 (1) 169.3 (1) O1i⋯H2ii—N2ii C(6)
O1⋯H1B—N1 2 α 1.852 (5) 2.871 (3) 171.5 (4) O1i⋯H1Biii—N1iii R22(8)
    β 1.943 (2) 2.955 (1) 168.7 (2) O1i⋯H1Biv—N1iv R22(8)
O2⋯H1A—N1 3 α 1.917 (3) 2.893 (2) 160.6 (5) O2i⋯H1Av—N1v C(8)
    β 1.818 (3) 2.843 (1) 177.3 (2) O2i⋯H1Aii—N1ii C(8)
O2⋯H2—N2 4 β 2.703 (2) 3.116 (1) 104.4 (1) O2i⋯H2vi—N2vi C(4)
N2⋯H1A—N1 5 β 2.690 3.000 97.37 N2i⋯H1Ai—N1i S(6)
Symmetry codes: (i) x, y, z; (ii) [1-x, y-{1\over 2}, -z+{1\over 2}]; (iii) -x-1, -y, -z; (iv) 1-x, 1-y, -z; (v) [-x-{1\over 2}, y+{1\over 2}, -z+{1\over 2}]; (vi) [1-x, -{1\over 2}+y,{1\over 2}-z].
[Figure 2]
Figure 2
Herring-bone arrangement of (a) dimers in the α-form of (I) and (b) dimers in the β form of (I). Hydrogen bonds are labelled according to the scheme used in Table 4[link]. Dimers are coloured for clarity only; chemically and crystallographically there is no difference between the differently coloured dimers.

Lattice-energy minimizations were performed in order to ascertain whether the differences between the neutron and X-ray molecular structures have a significant effect on computational modelling of this system. Comparison of the lattice parameters and lattice energies (approximately −0.4 and +0.7 kJ mol−1 for the α and β forms, respectively) obtained by the static rigid-molecule lattice-energy minimization (Table 5[link]) reveals that the differences are small but significant. In particular, they are significant:

  • (a) compared with the differences between the lattice-energy-minimized structures and the actual single-crystal neutron structures, which also reflect the errors in neglecting thermal effects at 30 K, the zero-point molecular motion, and errors in the intermolecular forces; and

  • (b) compared with the usual lattice-energy differences (ca 4–8 kJ mol−1) between polymorphs that exist under the same conditions of temperature and pressure (Bernstein, 2002[Bernstein, J. (2002). Polymorphism in Molecular Crystals. Oxford: Clarendon Press.]).

Table 5
Effects of computer modelling on the crystal structures

Positive values indicate an increase with respect to the lattice-energy-minimized (LEM) neutron unit cell

  LEM neutron structures Difference between LEM X-ray and LEM neutron structures Difference between LEM neutron structure and experimental neutron structure
α-AABA
a (Å) 4.874 −0.002 −0.015
b (Å) 14.562 −0.040 −0.167
c (Å) 12.359 −0.076 −0.109
β (°) 91.672 +0.183 +0.479
V3) 876.8 −8.2 −20.5
Lattice energy (kJ mol−1) −122.41 −0.42
       
β-AABA
a (Å) 7.856 +0.008 −0.068
b (Å) 9.270 −0.120 −0.298
c (Å) 12.650 +0.005 −0.103
β (°) 101.35 −0.50 −0.23
V3) 903.3 −9.0 −43.10
Lattice energy (kJ mol−1) −141.63 +0.69
       
ΔE§ 19.22 −1.11
       
†Lattice-energy-minimization calculations were performed as described in Coombes et al. (1996[Coombes, D. S., Price, S. L., Willock, D. J. & Leslie, M. (1996). J. Phys. Chem. 100, 7352-7360.]), keeping the neutron molecular structure rigid, and modelling the intermolecular forces by the FIT model potential and a distributed multipole model of the MP2 6-31G(d,p) charge density.
‡For the room-temperature X-ray structures, the corresponding wavefunctions were calculated using C—H and N—H bond lengths elongated to the standard neutron values of 1.08 and 1.01 Å, respectively (Allen et al., 1987[Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1-S19.]).
§ΔE is the difference between the lattice energies of the α and β polymorphs.

The more accurate neutron-derived model does reduce the difference in the lattice energy of the two forms by ca 1 kJ mol−1.

4. Conclusions

The crystal structures presented here represent a significant improvement upon existing X-ray derived structures and as such have removed a great deal of structural uncertainty, particularly with respect to the H-atom positions and atomic displacement parameters. The improved starting models yield small but significant improvements in the lattice-energy calculations, resulting in a slight reduction in the large (ca 20 kJ mol−1) lattice stabilization that results from the additional intermolecular hydrogen bond present in the β form. The structures thus provide a reliable starting point for future computational studies that seek to provide more reliable estimates of the relative stability of the two forms of (I).

Supporting information


Computing details top

Data collection: SXD-2001 (Gutmann, 2005) for aaba_alpha_30K; SXD-2001 for aaba_beta_30K. Cell refinement: SXD-2001 (Gutmann, 2005) for aaba_alpha_30K; SXD-2001 for aaba_beta_30K. Data reduction: SXD-2001 (Gutmann, 2005) for aaba_alpha_30K; SXD-2001 for aaba_beta_30K. For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1]
[Figure 2]
(aaba_alpha_30K) /a-o-acetoamidobenzoic acid top
Crystal data top
C9H10N2O2F(000) = 213
Mr = 178.19Dx = 1.382 Mg m3
Monoclinic, P21/nNeutron radiation, λ = 0.5-7.0 Å
a = 4.8591 (12) ÅCell parameters from 330 reflections
b = 14.395 (3) ŵ = 0.00 mm1
c = 12.250 (3) ÅT = 30 K
β = 92.151 (16)°Block, colourless
V = 856.3 (3) Å35.0 × 2.0 × 1.0 mm
Z = 4
Data collection top
SXD
diffractometer
Rint = 0.000
Radiation source: ISIS spallation sourceθmax = 81.7°, θmin = 8.7°
time–of–flight LAUE diffraction scansh = 73
5267 measured reflectionsk = 3136
5267 independent reflectionsl = 2928
5267 reflections with I > 2σ(I)
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.057All H-atom parameters refined
wR(F2) = 0.128 w = 1/[σ2(Fo2) + (0.0826P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max < 0.001
5267 reflectionsΔρmax = 2.00 e Å3
274 parametersΔρmin = 1.49 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.00129 (6)
Crystal data top
C9H10N2O2V = 856.3 (3) Å3
Mr = 178.19Z = 4
Monoclinic, P21/nNeutron radiation, λ = 0.5-7.0 Å
a = 4.8591 (12) ŵ = 0.00 mm1
b = 14.395 (3) ÅT = 30 K
c = 12.250 (3) Å5.0 × 2.0 × 1.0 mm
β = 92.151 (16)°
Data collection top
SXD
diffractometer
5267 reflections with I > 2σ(I)
5267 measured reflectionsRint = 0.000
5267 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0570 restraints
wR(F2) = 0.128All H-atom parameters refined
S = 1.04Δρmax = 2.00 e Å3
5267 reflectionsΔρmin = 1.49 e Å3
274 parameters
Special details top

Experimental. For peak integration a local UB matrix refined for each frame, using approximately 30 reflections from each of the 11 detectors. Hence _cell_measurement_reflns_used 330

For final cell dimensions a weighted average of all local cells was calculated

Because of the nature of the experiment, it is not possible to give values of theta_min and theta_max for the cell determination.

The same applies for the wavelength used for the experiment. The range of wavelengths used was 0.48–7.0 Angstroms, BUT the bulk of the diffraction information is obtained from wavelengths in the range 0.7–2.5 Angstroms.

The data collection procedures on the SXD instrument used for the single-crystal neutron data collection are most recently summarized in the Appendix to the following paper Wilson, C·C. (1997). J. Mol. Struct. 405, 207–217

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. The variable wavelength nature of the data collection procedure means that sensible values of _diffrn_reflns_theta_min & _diffrn_reflns_theta_max cannot be given instead the following limits are given

_diffrn_reflns_sin(theta)/lambda_min 0.05 _diffrn_reflns_sin(theta)/lambda_max 1.31

_refine_diff_density_max/min is given in Fermi per per angstrom cubed not electons per angstrom cubed. Another way to consider the _refine_diff_density_ is as a percentage of the diffracted intensity of a given atom: _refine_diff_density_max = 5% of Carbon _refine_diff_density_min = −4% of Carbon

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
O10.3257 (5)0.11090 (10)0.00091 (10)0.0083 (5)
O20.2943 (6)0.42403 (10)0.16253 (11)0.0102 (5)
N10.2414 (3)0.01111 (7)0.11383 (7)0.0096 (3)
N20.2672 (3)0.27463 (6)0.09767 (7)0.0075 (3)
C10.0625 (5)0.23375 (9)0.16623 (9)0.0046 (4)
C20.0229 (5)0.13613 (9)0.15779 (9)0.0053 (4)
C30.1868 (5)0.09345 (8)0.22104 (10)0.0067 (4)
C40.3557 (5)0.14459 (9)0.29321 (9)0.0065 (4)
C50.3090 (5)0.23967 (9)0.30440 (9)0.0070 (4)
C60.1029 (5)0.28459 (9)0.24204 (10)0.0066 (4)
C70.2071 (4)0.07776 (9)0.08497 (9)0.0053 (4)
C80.3744 (5)0.36174 (9)0.09990 (9)0.0066 (4)
C90.6077 (5)0.37851 (9)0.01622 (10)0.0080 (4)
H60.0699 (11)0.3586 (2)0.2504 (3)0.0205 (10)
H1B0.3817 (11)0.0498 (2)0.0687 (2)0.0210 (10)
H20.3478 (10)0.2288 (2)0.0410 (2)0.0183 (9)
H30.2219 (12)0.0192 (2)0.2119 (3)0.0234 (11)
H1A0.1833 (11)0.0332 (2)0.1899 (2)0.0203 (10)
H50.4365 (11)0.2813 (2)0.3620 (2)0.0227 (10)
H40.5204 (11)0.1095 (2)0.3401 (3)0.0218 (10)
H9C0.6831 (13)0.3139 (2)0.0197 (3)0.0337 (14)
H9B0.5367 (13)0.4225 (3)0.0481 (3)0.0335 (13)
H9A0.7695 (13)0.4152 (3)0.0554 (3)0.0352 (14)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0148 (17)0.0045 (5)0.0055 (4)0.0011 (7)0.0029 (6)0.0005 (4)
O20.0182 (16)0.0052 (5)0.0069 (5)0.0011 (8)0.0021 (7)0.0030 (4)
N10.0164 (10)0.0062 (3)0.0062 (3)0.0018 (5)0.0016 (4)0.0009 (2)
N20.0112 (9)0.0051 (3)0.0060 (3)0.0008 (5)0.0014 (4)0.0008 (2)
C10.0055 (12)0.0039 (5)0.0043 (4)0.0011 (6)0.0003 (5)0.0005 (3)
C20.0078 (13)0.0038 (4)0.0041 (4)0.0002 (6)0.0003 (5)0.0002 (3)
C30.0088 (13)0.0048 (5)0.0063 (4)0.0006 (7)0.0012 (6)0.0001 (3)
C40.0057 (14)0.0081 (5)0.0055 (4)0.0005 (6)0.0014 (6)0.0004 (4)
C50.0073 (13)0.0085 (5)0.0051 (4)0.0015 (7)0.0012 (6)0.0005 (3)
C60.0083 (13)0.0058 (5)0.0056 (4)0.0006 (6)0.0020 (5)0.0006 (3)
C70.0087 (13)0.0037 (4)0.0035 (4)0.0005 (6)0.0012 (5)0.0005 (3)
C80.0118 (13)0.0047 (5)0.0034 (4)0.0000 (6)0.0004 (5)0.0003 (3)
C90.0092 (14)0.0078 (5)0.0068 (4)0.0012 (6)0.0009 (6)0.0008 (3)
H60.024 (3)0.0103 (11)0.0266 (13)0.0029 (16)0.0047 (16)0.0032 (9)
H1B0.028 (3)0.0161 (12)0.0181 (11)0.0101 (17)0.0044 (15)0.0013 (9)
H20.022 (3)0.0155 (12)0.0168 (11)0.0002 (17)0.0103 (13)0.0034 (9)
H30.032 (4)0.0106 (11)0.0272 (13)0.0007 (17)0.0037 (17)0.0011 (10)
H1A0.026 (3)0.0201 (13)0.0147 (11)0.0012 (17)0.0068 (14)0.0058 (9)
H50.024 (3)0.0228 (14)0.0206 (12)0.0059 (18)0.0104 (15)0.0049 (10)
H40.016 (3)0.0240 (15)0.0242 (13)0.0083 (19)0.0121 (15)0.0014 (11)
H9C0.045 (4)0.0150 (13)0.0391 (18)0.000 (2)0.019 (2)0.0036 (13)
H9B0.037 (4)0.041 (2)0.0220 (14)0.002 (2)0.0002 (18)0.0173 (13)
H9A0.033 (4)0.045 (2)0.0286 (16)0.017 (3)0.007 (2)0.0043 (15)
Geometric parameters (Å, º) top
O1—C71.255 (2)C3—C41.393 (3)
O2—C81.234 (2)C3—H31.088 (3)
N1—C71.3394 (16)C4—C51.395 (2)
N1—H1B1.026 (4)C4—H41.092 (5)
N1—H1A1.015 (3)C5—C61.396 (3)
N2—C81.3586 (18)C5—H51.099 (4)
N2—C11.406 (2)C6—H61.082 (3)
N2—H21.025 (3)C8—C91.519 (3)
C1—C61.410 (3)C9—H9C1.087 (4)
C1—C21.4226 (18)C9—H9B1.078 (4)
C2—C31.399 (3)C9—H9A1.076 (5)
C2—C71.498 (2)
C7—N1—H1B117.6 (2)C4—C5—C6121.11 (16)
C7—N1—H1A120.6 (2)C4—C5—H5120.6 (3)
H1B—N1—H1A118.8 (3)C6—C5—H5118.3 (3)
C8—N2—C1129.60 (12)C5—C6—C1119.98 (13)
C8—N2—H2118.1 (3)C5—C6—H6120.6 (3)
C1—N2—H2112.3 (2)C1—C6—H6119.4 (3)
N2—C1—C6123.29 (12)O1—C7—N1121.45 (16)
N2—C1—C2117.68 (14)O1—C7—C2121.42 (13)
C6—C1—C2119.03 (17)N1—C7—C2117.13 (13)
C3—C2—C1119.42 (16)O2—C8—N2124.83 (19)
C3—C2—C7119.35 (13)O2—C8—C9120.95 (15)
C1—C2—C7121.20 (17)N2—C8—C9114.22 (12)
C4—C3—C2121.24 (13)C8—C9—H9C111.7 (3)
C4—C3—H3119.6 (3)C8—C9—H9B109.6 (4)
C2—C3—H3119.2 (3)H9C—C9—H9B108.6 (3)
C3—C4—C5119.13 (17)C8—C9—H9A108.5 (3)
C3—C4—H4119.5 (2)H9C—C9—H9A111.1 (5)
C5—C4—H4121.4 (2)H9B—C9—H9A107.2 (4)
(aaba_beta_30K) /b-o-acetoamidobenzoic acid top
Crystal data top
C9H10N2O2Z = 4
Mr = 178.19F(000) = 211
Monoclinic, P21/cDx = 1.376 Mg m3
a = 7.788 (1) ÅNeutron radiation, λ = 0.69-5.9 Å
b = 8.972 (2) ÅCell parameters from 400 reflections
c = 12.547 (2) ÅT = 30 K
β = 101.12 (1)°Block, colourless
V = 860.2 (3) Å33.5 × 1.5 × 1.5 mm
Data collection top
SXD
diffractometer
11484 reflections with I > 2σ(I)
Radiation source: ISIS spallation sourceRint = 0.000
time–of–flight LAUE diffraction scansθmax = 82.5°, θmin = 8.2°
Absorption correction: gaussian
Gaussian intigration method applied thought SXD-2001 program
h = 2116
Tmin = ?, Tmax = ?k = 1519
11484 measured reflectionsl = 3327
11484 independent reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.058All H-atom parameters refined
wR(F2) = 0.148 w = 1/[σ2(Fo2) + (0.0926P)2 + 11.2116P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max < 0.001
11484 reflectionsΔρmax = 2.35 e Å3
274 parametersΔρmin = 2.38 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0450 (7)
Crystal data top
C9H10N2O2β = 101.12 (1)°
Mr = 178.19V = 860.2 (3) Å3
Monoclinic, P21/cZ = 4
a = 7.788 (1) ÅNeutron radiation, λ = 0.69-5.9 Å
b = 8.972 (2) ÅT = 30 K
c = 12.547 (2) Å3.5 × 1.5 × 1.5 mm
Data collection top
SXD
diffractometer
11484 independent reflections
Absorption correction: gaussian
Gaussian intigration method applied thought SXD-2001 program
11484 reflections with I > 2σ(I)
Tmin = ?, Tmax = ?Rint = 0.000
11484 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0580 restraints
wR(F2) = 0.148All H-atom parameters refined
S = 1.03 w = 1/[σ2(Fo2) + (0.0926P)2 + 11.2116P]
where P = (Fo2 + 2Fc2)/3
11484 reflectionsΔρmax = 2.35 e Å3
274 parametersΔρmin = 2.38 e Å3
Special details top

Experimental. For peak integration a local UB matrix refined for each frame, using approximately 35–40 reflections from each of the 11 detectors. Hence _cell_measurement_reflns_used 400

For final cell dimensions a weighted average of all local cells was calculated

Because of the nature of the experiment, it is not possible to give values of theta_min and theta_max for the cell determination.

The same applies for the wavelength used for the experiment. The range of wavelengths used was 0.69–5.9 Angstroms, BUT the bulk of the diffraction information is obtained from wavelengths in the range 0.7–2.5 Angstroms.

The data collection procedures on the SXD instrument used for the single-crystal neutron data collection are most recently summarized in the Appendix to the following paper Wilson, C·C. (1997). J. Mol. Struct. 405, 207–217.

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. The variable wavelength nature of the data collection procedure means that sensible values of _diffrn_reflns_theta_min & _diffrn_reflns_theta_max cannot be given instead the following limits are given

_diffrn_reflns_sin(theta)/lambda_min 0.06 _diffrn_reflns_sin(theta)/lambda_max 1.37

_refine_diff_density_max/min is given in Fermi per per angstrom cubed not electons per angstrom cubed. Another way to consider the _refine_diff_density_ is as a percentage of the diffracted intensity of a given atom: _refine_diff_density_max = 3% of Carbon _refine_diff_density_min = −3% of Carbon

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
O10.30407 (8)0.45434 (11)0.06498 (5)0.00571 (13)
O20.45233 (9)0.44751 (12)0.32723 (6)0.00736 (13)
N10.49421 (5)0.64900 (7)0.09770 (3)0.00633 (9)
N20.46827 (5)0.69965 (7)0.33038 (3)0.00516 (8)
C10.29204 (7)0.72026 (9)0.27464 (4)0.00442 (11)
C20.23108 (7)0.65871 (9)0.17126 (4)0.00428 (10)
C30.05534 (7)0.67694 (10)0.12146 (5)0.00569 (12)
C40.05798 (7)0.75886 (10)0.17259 (5)0.00678 (12)
C50.00313 (8)0.82164 (10)0.27477 (5)0.00708 (12)
C60.17756 (7)0.80121 (10)0.32588 (5)0.00657 (12)
C70.34806 (7)0.57761 (9)0.10839 (4)0.00400 (10)
C80.53825 (7)0.56233 (9)0.35385 (4)0.00510 (11)
C90.72597 (8)0.55796 (11)0.41339 (5)0.00847 (13)
H20.5428 (2)0.7909 (3)0.35617 (16)0.0200 (4)
H1B0.5733 (2)0.6050 (3)0.04917 (15)0.0196 (4)
H30.0071 (2)0.6274 (3)0.04198 (13)0.0201 (4)
H1A0.5146 (2)0.7555 (3)0.12716 (15)0.0191 (4)
H60.2260 (2)0.8474 (3)0.40600 (13)0.0226 (5)
H40.19351 (19)0.7759 (3)0.13325 (15)0.0224 (4)
H50.0857 (2)0.8848 (3)0.31499 (15)0.0233 (5)
H9C0.7817 (3)0.6684 (3)0.4312 (2)0.0295 (5)
H9B0.8041 (3)0.4982 (5)0.3639 (2)0.0379 (8)
H9A0.7330 (3)0.4966 (4)0.48892 (18)0.0376 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.00659 (18)0.0037 (4)0.00728 (19)0.0009 (2)0.00238 (16)0.00190 (19)
O20.0077 (2)0.0026 (4)0.0109 (2)0.0003 (2)0.00037 (18)0.0003 (2)
N10.00616 (12)0.0052 (3)0.00854 (14)0.00169 (13)0.00359 (10)0.00214 (13)
N20.00535 (11)0.0034 (2)0.00629 (12)0.00002 (12)0.00012 (10)0.00020 (12)
C10.00465 (15)0.0037 (3)0.00495 (16)0.00035 (16)0.00107 (13)0.00051 (15)
C20.00377 (14)0.0043 (3)0.00481 (16)0.00002 (16)0.00082 (12)0.00085 (15)
C30.00390 (15)0.0060 (4)0.00698 (17)0.00037 (16)0.00043 (13)0.00132 (17)
C40.00438 (16)0.0071 (4)0.00897 (19)0.00099 (18)0.00144 (14)0.00128 (18)
C50.00594 (16)0.0064 (4)0.00921 (19)0.00153 (19)0.00230 (14)0.00176 (18)
C60.00627 (16)0.0074 (4)0.00629 (17)0.00132 (18)0.00184 (14)0.00220 (17)
C70.00433 (14)0.0031 (3)0.00484 (15)0.00012 (16)0.00142 (12)0.00076 (15)
C80.00522 (15)0.0038 (3)0.00590 (16)0.00030 (17)0.00018 (13)0.00009 (16)
C90.00635 (17)0.0080 (4)0.00988 (19)0.00101 (19)0.00125 (15)0.0001 (2)
H20.0171 (5)0.0125 (10)0.0280 (7)0.0038 (6)0.0013 (5)0.0021 (7)
H1B0.0182 (5)0.0198 (13)0.0239 (6)0.0004 (6)0.0121 (5)0.0068 (6)
H30.0179 (5)0.0254 (13)0.0153 (5)0.0003 (6)0.0007 (4)0.0070 (6)
H1A0.0209 (6)0.0130 (11)0.0244 (6)0.0056 (6)0.0071 (5)0.0065 (6)
H60.0232 (6)0.0286 (15)0.0148 (5)0.0029 (7)0.0008 (5)0.0093 (6)
H40.0100 (4)0.0301 (14)0.0252 (7)0.0041 (6)0.0012 (4)0.0028 (7)
H50.0180 (6)0.0277 (15)0.0254 (7)0.0076 (7)0.0075 (5)0.0085 (7)
H9C0.0222 (7)0.0171 (14)0.0444 (11)0.0047 (8)0.0057 (7)0.0049 (10)
H9B0.0194 (7)0.053 (3)0.0415 (11)0.0091 (9)0.0056 (7)0.0212 (12)
H9A0.0301 (9)0.050 (2)0.0278 (9)0.0049 (11)0.0060 (7)0.0216 (11)
Geometric parameters (Å, º) top
O1—C71.2511 (12)C3—C41.3960 (10)
O2—C81.2387 (12)C3—H31.0902 (17)
N1—C71.3351 (8)C4—C51.3972 (9)
N1—H1B1.0249 (17)C4—H41.0863 (15)
N1—H1A1.025 (2)C5—C61.3979 (8)
N2—C81.3564 (10)C5—H51.090 (2)
N2—C11.4272 (7)C6—H61.0856 (17)
N2—H21.020 (2)C8—C91.5085 (8)
C1—C61.3988 (9)C9—H9C1.087 (3)
C1—C21.4055 (8)C9—H9B1.090 (3)
C2—C31.4002 (7)C9—H9A1.088 (2)
C2—C71.5029 (9)
C7—N1—H1B119.78 (14)C4—C5—C6119.80 (6)
C7—N1—H1A119.09 (11)C4—C5—H5120.00 (11)
H1B—N1—H1A120.25 (18)C6—C5—H5120.19 (11)
C8—N2—C1122.16 (6)C5—C6—C1120.42 (6)
C8—N2—H2118.71 (12)C5—C6—H6120.54 (12)
C1—N2—H2119.08 (13)C1—C6—H6119.04 (12)
C6—C1—C2119.76 (5)O1—C7—N1123.20 (6)
C6—C1—N2118.68 (5)O1—C7—C2120.91 (6)
C2—C1—N2121.55 (6)N1—C7—C2115.80 (7)
C3—C2—C1119.55 (6)O2—C8—N2121.55 (6)
C3—C2—C7117.49 (5)O2—C8—C9122.24 (8)
C1—C2—C7122.93 (5)N2—C8—C9116.20 (7)
C4—C3—C2120.43 (6)C8—C9—H9C112.85 (14)
C4—C3—H3119.88 (11)C8—C9—H9B108.97 (13)
C2—C3—H3119.69 (11)H9C—C9—H9B108.7 (3)
C3—C4—C5120.02 (5)C8—C9—H9A109.01 (14)
C3—C4—H4120.67 (13)H9C—C9—H9A109.3 (2)
C5—C4—H4119.31 (13)H9B—C9—H9A107.9 (3)

Experimental details

(aaba_alpha_30K)(aaba_beta_30K)
Crystal data
Chemical formulaC9H10N2O2C9H10N2O2
Mr178.19178.19
Crystal system, space groupMonoclinic, P21/nMonoclinic, P21/c
Temperature (K)3030
a, b, c (Å)4.8591 (12), 14.395 (3), 12.250 (3)7.788 (1), 8.972 (2), 12.547 (2)
β (°) 92.151 (16) 101.12 (1)
V3)856.3 (3)860.2 (3)
Z44
Radiation typeNeutron, λ = 0.5-7.0 ÅNeutron, λ = 0.69-5.9 Å
µ (mm1)0.00?
Crystal size (mm)5.0 × 2.0 × 1.03.5 × 1.5 × 1.5
Data collection
DiffractometerSXD
diffractometer
SXD
diffractometer
Absorption correctionGaussian
Gaussian intigration method applied thought SXD-2001 program
No. of measured, independent and
observed [I > 2σ(I)] reflections
5267, 5267, 5267 11484, 11484, 11484
Rint0.0000.000
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.057, 0.128, 1.04 0.058, 0.148, 1.03
No. of reflections526711484
No. of parameters274274
H-atom treatmentAll H-atom parameters refinedAll H-atom parameters refined
w = 1/[σ2(Fo2) + (0.0826P)2]
where P = (Fo2 + 2Fc2)/3
w = 1/[σ2(Fo2) + (0.0926P)2 + 11.2116P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)2.00, 1.492.35, 2.38

Computer programs: SXD-2001 (Gutmann, 2005), SXD-2001, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), SHELXTL.

 

Footnotes

1Supplementary data for this paper are available from the IUCr electronic archives (Reference: BM5034 ). Services for accessing these data are described at the back of the journal.

Acknowledgements

This work was funded by RCUK through the Control and Prediction of the Organic Solid State (CPOSS) project (GR/S24114/01, http://www.cposs.org.uk ). Neutron beamtime on SXD at ISIS was provided by CCLRC (Council for the Central Laboratory of the Research Councils). The authors would like to thank Professor S. L. Price for helpful discussions on the lattice-energy minimization work.

References

First citationAllen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–S19. CrossRef Web of Science
First citationBaker, B. R. & Almaula, P. I. (1962). J. Org. Chem. 27, 4672–4674. CrossRef CAS
First citationBernstein, J. (2002). Polymorphism in Molecular Crystals. Oxford: Clarendon Press.
First citationButtar, D., Charlton, M. H., Docherty, R. & Starbuck. J. (1998). J. Chem. Soc. Perkin Trans. 2, pp. 763–772.
First citationCoombes, D. S., Price, S. L., Willock, D. J. & Leslie, M. (1996). J. Phys. Chem. 100, 7352–7360. CrossRef CAS Web of Science
First citationDay, G. M. (2002). PhD thesis. University College London.
First citationErrede, L. A., Etter, M. C., Williams, R. C. & Darnauer. S. M. (1981). J. Chem. Soc. Perkin Trans. 2, pp. 233–238. CSD CrossRef
First citationEtter, M. C. (1983). Mol. Cryst. Liq. Cryst. 93, 95–100. CrossRef CAS
First citationEtter, M. C. (1990). Acc. Chem. Res. 23, 120–126. CrossRef CAS Web of Science
First citationGutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.
First citationKaramertzanis, P. G. & Price, S. L. (2006). J. Chem. Theory Comput. 2, 1184–1199. Web of Science CrossRef CAS
First citationKeen, D. A., Gutmann, M. J. & Wilson, C. C. (2006). J. Appl. Cryst. 39, 714–722. Web of Science CrossRef CAS IUCr Journals
First citationKeen, D. A. & Wilson, C. C. (1996). Report RAL-TR-96–083. Rutherford Appleton Laboratory, Oxfordshire, England.
First citationMourik, T. van, Karamertzanis, P. G. & Price, S. L. (2006). J. Phys. Chem. A, 110, 8–12. Web of Science CrossRef PubMed
First citationNowell, H. & Price, S. L. (2005). Acta Cryst. B61, 558–568. Web of Science CSD CrossRef CAS IUCr Journals
First citationSheldrick, G. M. (1990). Acta Cryst. A46, 467–473. CrossRef CAS Web of Science IUCr Journals
First citationSheldrick, G. M. (1997a). SHELXL97. University of Göttingen, Germany.
First citationSheldrick, G. M. (1997b). SHELXTL, Version 5.03. Bruker AXS Inc., Madison, Wisconsin, USA.
First citationWilson, C. C. (1990). IOP Conf. Ser. 107, 145.

© International Union of Crystallography. Prior permission is not required to reproduce short quotations, tables and figures from this article, provided the original authors and source are cited. For more information, click here.

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
Follow Acta Cryst. B
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds