1. Study of the nature and role of nanoscale order in complex materials
D.J.Goossens
AINSE Research Fellow, ANU
Research School of Chemistry & Department of Physics

2. An example study: PCNB, C6Cl5NO2
PCNB is one of a series of chloronitrobenzene derivatives being studied
Disordered nature & propensity to undergo phase-transitions
Anomalous dielectric properties, NLO.
DISORDER often strongly affects the electronic environment and…
…is fundamental to physical properties
e.g. second harmonic generation.

3. Structural details

4. The Data (APS) Small horizontal bands Strong peak asymmetry
Vertical streaks
Small horizontal bands
Strong peak asymmetry

5. Analysis of diffuse scattering
single crystal
Synchrotron
diffraction experiment
observed diffuse
scattering data
Compare
adjust model
Model crystal
Monte Carlo
Computer simulation
calculated data

6. Constructing the Model
out-of-plane
within-plane

7. Size-effect NN
NCl
ClN
ClCl
average

8. Size-effect (2)

9. Scatter plots
Cl…Cl
Cl…N
N…N

10. Calculated and Observed

11. Conclusions (PCNB)
We have a model crystal whose ordering reflects that in the real system. This provides exceptional insight into the structure. For example:
NO2 groups do not order, even on short range.
NO2 groups push each other apart (‘size-effect’)
We get detailed ADPs for each atom, and they need not be able to be modelled by ellipsoids.
We can separate the components of ADPs due to the size-effect (static) from other components (probably dynamic)
This gives insight into molecular dynamics in the solid state, and deeper structural knowledge.
For example, dielectric properties are not due to ordering of NO2 groups.

12. Ibuprofen
Using diffuse scattering to study the molecular conformations and interactions in a pharmaceutical.

13. Observed and Calculated

14. Examining the model
Correlations between molecules connected by contact vectors of type 1 (top row), 2 (middle row) & 3 (bottom row) in the three basal planes of Ibuprofen.

15. Examining the model (2)
Correlations between molecules connected by contact vectors of type 1 (top row), 2 (middle row) & 3 (bottom row) in the three basal planes of Ibuprofen.
A scatter plot of the distribution of the values of the dihedral angles on C3 (φ1 ) and O1 (φ2 ) that give minimum molecular energy.

16. Conclusions (Ibuprofen)
For Ibuprofen, the strongest contact vector was found to coincide with the -COOH--HOOC- interaction which dimerises pairs of molecules.
Important molecular degrees of freedom were torsional motions of C3 (angle φ1 ), O1 (angle φ2 ) and C11 (angle φ3 ).
Of these, the motions of C1 and O1 interact directly but weakly via a cross term in the energy, while C3 and C11 are substantially negatively correlated
Between molecules, components of the positional coordinates are correlated when they coincide with the direction of propagation of certain intermolecular contacts.

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