O'HARE GROUP

 

In-situ diffraction studies

We report the first use of high-energy monochromatic in situ X-ray powder diffraction to gain unprecedented insights into the chemical processes occurring during high temperature, lab-scale metal oxide syntheses. During the flux synthesis of the n = 4 Aurivillius phase, Bi5Ti3Fe0.5Cr0.5O15 at 950 °C in molten Na2SO4 we observe the progression of numerous metastable phases. Using sequential multiphase Rietveld refinement of the time-dependent in situ XRD data, we are able to obtain mechanistic understanding of this reaction under a range of conditions.

Understanding the driving forces controlling crystallization is essential for the efficient synthesis and design of new materials, particularly metal–organic frameworks (MOFs), where mild solvothermal synthesis often allows access to various phases from the same reagents. Using high-energy in situ synchrotron X-ray powder diffraction, we monitor the crystallization of lithium tartrate MOFs, observing the successive crystallization and dissolution of three competing phases in one reaction. By determining rate constants and activation energies, we fully quantify the reaction energy landscape, gaining important predictive power for the choice of reaction conditions. Different reaction rates are explained by the structural relationships between the products and the reactants; larger changes in conformation result in higher activation energies. The methods we demonstrate can easily be applied to other materials, opening the door to a greater understanding of crystallization in general.

 

Recent publications:

Time-resolved in situ powder X-ray diffraction reveals the mechanisms of molten salt synthesis, S. J. Moorhouse, Y. Wu, H. C. Buckley and D. O’Hare, Chem. Commun., (2016), 52, 13865-13868.

Time-Resolved In Situ X-ray Diffraction Reveals Metal-Dependent Metal-Organic Framework Formation, Y. Wu, S. Henke, G. Kieslich, I. Schwedler, M. Yang, D. A. X. Fraser and D. O’Hare, Angew. Chemie Int. Ed., (2016), 55, 14081-14084

Simultaneous Differential Scanning Calorimetry-Synchrotron X-ray Powder Diffraction: A Powerful Technique for Physical Form Characterization in Pharmaceutical Materials, A. Clout, A. B. M. Buanz, T. J. Prior, C. Reinhard, Y. Wu, D. O’Hare, G. R. Williams and S. Gaisford, Anal. Chem., (2016), 88, 10111-10117

Exchange of Coordinated Solvent During Crystallization of a Metal-Organic Framework Observed by In Situ High-Energy X-ray Diffraction, Y. Wu, M. I. Breeze, G. J. Clarkson, F. Millange, D. O’Hare and R. I. Walton, Angew. Chemie Int. Ed., (2016), 55, 4992-4996.

In Situ Observation of Successive Crystallizations and Metastable Intermediates in the Formation of Metal-Organic Frameworks, H. H.-M. Yeung, Y. Wu, S. Henke, A. K. Cheetham, D. O'Hare, R. I. Walton, Angew. Chem. Int. Ed., (2016), 55, 2012-2016.

http://ohare.chem.ox.ac.uk/in-situ-diffraction-studies.aspx