Buy article online - an online subscription or single-article purchase is required to access this article.
Single-crystal diffuse X-ray scattering from paracetamol polymorphs is successfully calculated with Monte Carlo (MC) models that are used to simulate the crystals. In order to obtain the correct model appropriate force constants are required that describe the interatomic potentials used in the MC algorithm. Coefficients for an empirical `Buckingham'-type formula are used to determine these force constants. These coefficients are subsequently refined using the least-squares method and are found to converge on similar values for both polymorphic forms. An investigation of the correlation space generated from each model provides what would be expected given that strong displacive correlations exist between the molecules comprising the densely hydrogen-bonded layers. More disordered motions between these layers are present in the model for form (II) as opposed to form (I). An investigation into the peculiarities of librational disorder was also conducted, however, correlation values turn out to be so small that any structural information concerning librational correlation is inconclusive. The purpose of this experiment was to identify if the diffuse scattering features could provide further insight into understanding the physical reasoning behind the metastability of form (II). The form (II) → (I) phase transition is also not currently well understood and usually phase transitional information can be obtained from pronounced diffuse scattering features. Since the diffuse scattering is modelled adequately using harmonic potentials it is our conjecture that the `diffuse' is essentially thermal in origin and does not afford any extra information about the form (II) → (I) phase transition.
Supporting information
CCDC reference: 866775
Data collection: Collect (Bruker AXS BV, 1997-2004); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor 1997); program(s) used to solve structure: known; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Xtal3.7 (Hall et al., 2001); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).
Crystal data top
C8H9NO2 | F(000) = 640 |
Mr = 151.16 | Dx = 1.339 Mg m−3 |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 10043 reflections |
a = 11.8237 (4) Å | θ = 2.6–27.5° |
b = 7.3971 (3) Å | µ = 0.10 mm−1 |
c = 17.1526 (7) Å | T = 293 K |
V = 1500.19 (10) Å3 | Prism, colourless |
Z = 8 | 0.35 × 0.15 × 0.09 mm |
Data collection top
KappaCCD diffractometer | 1704 independent reflections |
Radiation source: fine-focus sealed tube | 1178 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.037 |
Detector resolution: 9 pixels mm-1 | θmax = 27.4°, θmin = 2.9° |
CCD scans | h = −15→11 |
Absorption correction: integration Gaussian integration (Coppens, 1970) | k = −9→7 |
Tmin = 0.967, Tmax = 0.991 | l = −22→17 |
7284 measured reflections | |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.040 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.117 | All H-atom parameters refined |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0618P)2 + 0.1916P] where P = (Fo2 + 2Fc2)/3 |
1704 reflections | (Δ/σ)max < 0.001 |
136 parameters | Δρmax = 0.15 e Å−3 |
0 restraints | Δρmin = −0.18 e Å−3 |
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 | x | y | z | Uiso*/Ueq | |
C1 | −0.05363 (10) | 0.29200 (19) | 0.16106 (7) | 0.0371 (3) | |
C2 | −0.16057 (11) | 0.2127 (2) | 0.16301 (8) | 0.0399 (4) | |
C3 | −0.22081 (11) | 0.2076 (2) | 0.23192 (8) | 0.0402 (4) | |
C4 | −0.17645 (11) | 0.2809 (2) | 0.29949 (8) | 0.0387 (3) | |
C5 | −0.07201 (11) | 0.3659 (2) | 0.29691 (8) | 0.0406 (4) | |
C6 | −0.01126 (11) | 0.3705 (2) | 0.22827 (8) | 0.0397 (4) | |
N7 | 0.01806 (10) | 0.29092 (18) | 0.09458 (7) | 0.0447 (4) | |
C8 | −0.00639 (12) | 0.2609 (2) | 0.01959 (8) | 0.0465 (4) | |
O9 | −0.10325 (9) | 0.2285 (2) | −0.00299 (6) | 0.0698 (4) | |
C10 | 0.09303 (16) | 0.2693 (4) | −0.03459 (11) | 0.0613 (5) | |
O11 | −0.23691 (9) | 0.26928 (17) | 0.36757 (6) | 0.0545 (3) | |
H12 | −0.1908 (13) | 0.160 (2) | 0.1177 (9) | 0.046 (4)* | |
H13 | −0.2932 (13) | 0.153 (2) | 0.2342 (8) | 0.046 (4)* | |
H14 | −0.0426 (12) | 0.425 (2) | 0.3441 (9) | 0.050 (4)* | |
H15 | 0.0637 (13) | 0.430 (2) | 0.2268 (8) | 0.045 (4)* | |
H16 | 0.0891 (17) | 0.310 (2) | 0.1063 (10) | 0.058 (5)* | |
H17 | 0.126 (3) | 0.154 (4) | −0.0426 (19) | 0.145 (12)* | |
H18 | 0.156 (2) | 0.338 (4) | −0.0164 (14) | 0.111 (8)* | |
H19 | 0.069 (2) | 0.306 (3) | −0.0843 (15) | 0.089 (7)* | |
H20 | −0.188 (2) | 0.279 (3) | 0.4098 (14) | 0.083 (7)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0287 (6) | 0.0494 (8) | 0.0332 (7) | 0.0019 (5) | −0.0013 (6) | 0.0049 (6) |
C2 | 0.0305 (6) | 0.0535 (9) | 0.0358 (7) | −0.0022 (6) | −0.0049 (6) | −0.0009 (6) |
C3 | 0.0264 (6) | 0.0523 (9) | 0.0419 (8) | −0.0026 (5) | −0.0014 (6) | 0.0041 (6) |
C4 | 0.0304 (6) | 0.0505 (9) | 0.0353 (7) | 0.0049 (6) | 0.0013 (5) | 0.0038 (6) |
C5 | 0.0368 (7) | 0.0480 (9) | 0.0369 (7) | −0.0011 (6) | −0.0046 (6) | −0.0021 (6) |
C6 | 0.0288 (6) | 0.0486 (9) | 0.0419 (8) | −0.0050 (6) | −0.0034 (5) | 0.0015 (6) |
N7 | 0.0280 (6) | 0.0715 (10) | 0.0347 (6) | −0.0035 (5) | −0.0001 (5) | 0.0027 (5) |
C8 | 0.0371 (7) | 0.0651 (10) | 0.0372 (8) | −0.0009 (6) | 0.0011 (6) | 0.0027 (7) |
O9 | 0.0405 (6) | 0.1312 (12) | 0.0375 (6) | −0.0133 (6) | −0.0037 (5) | −0.0018 (6) |
C10 | 0.0458 (9) | 0.0967 (16) | 0.0414 (9) | −0.0037 (9) | 0.0079 (8) | −0.0008 (9) |
O11 | 0.0356 (6) | 0.0923 (9) | 0.0356 (6) | −0.0018 (5) | 0.0037 (5) | 0.0013 (5) |
Geometric parameters (Å, º) top
C1—C6 | 1.3847 (19) | C5—H14 | 0.984 (16) |
C1—C2 | 1.3941 (18) | C6—H15 | 0.989 (15) |
C1—N7 | 1.4209 (18) | N7—C8 | 1.3369 (19) |
C2—C3 | 1.381 (2) | N7—H16 | 0.875 (19) |
C2—H12 | 0.940 (16) | C8—O9 | 1.2325 (18) |
C3—C4 | 1.383 (2) | C8—C10 | 1.500 (2) |
C3—H13 | 0.948 (15) | C10—H17 | 0.95 (3) |
C4—O11 | 1.3719 (16) | C10—H18 | 0.96 (3) |
C4—C5 | 1.3864 (19) | C10—H19 | 0.94 (3) |
C5—C6 | 1.3795 (19) | O11—H20 | 0.93 (3) |
| | | |
C6—C1—C2 | 118.98 (12) | C5—C6—H15 | 120.0 (8) |
C6—C1—N7 | 117.05 (11) | C1—C6—H15 | 119.2 (8) |
C2—C1—N7 | 123.91 (12) | C8—N7—C1 | 130.10 (12) |
C3—C2—C1 | 120.00 (13) | C8—N7—H16 | 117.1 (11) |
C3—C2—H12 | 120.0 (9) | C1—N7—H16 | 112.8 (11) |
C1—C2—H12 | 119.9 (9) | O9—C8—N7 | 122.38 (13) |
C2—C3—C4 | 120.73 (13) | O9—C8—C10 | 122.79 (15) |
C2—C3—H13 | 120.9 (9) | N7—C8—C10 | 114.83 (14) |
C4—C3—H13 | 118.4 (9) | C8—C10—H17 | 112.0 (19) |
O11—C4—C3 | 119.41 (13) | C8—C10—H18 | 115.6 (15) |
O11—C4—C5 | 121.31 (12) | H17—C10—H18 | 102 (2) |
C3—C4—C5 | 119.27 (12) | C8—C10—H19 | 110.0 (14) |
C6—C5—C4 | 120.15 (12) | H17—C10—H19 | 104 (2) |
C6—C5—H14 | 120.4 (9) | H18—C10—H19 | 112 (2) |
C4—C5—H14 | 119.4 (9) | C4—O11—H20 | 109.5 (13) |
C5—C6—C1 | 120.78 (12) | | |
Subscribe to Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
The full text of this article is available to subscribers to the journal.
If you have already registered and are using a computer listed in your registration details, please email
support@iucr.org for assistance.