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

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.

Structural details

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

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

Constructing the Model out-of-plane within-plane

Size-effect NN NCl ClN ClCl average

Size-effect (2)

Scatter plots Cl…Cl Cl…N N…N

Calculated and Observed

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.

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

Observed and Calculated

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.

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.

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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