Understanding the agglomerate crystallisation of hexamine through X-ray microscopy and crystallographic modelling
The detailed molecular-scale mechanism of the growth of organic crystals underpins a diversity of phenomena, such as the isolation and purification of high-quality materials for the pharmaceutical and fine chemical sectors. Recent advances in X-ray Microscopy (XRM) and complementary diffraction contrast tomography (DCT) have enabled the detailed characterisation of the micro-structure of hexamine agglomerates. Detailed XRM analysis of the growth history and micro-structure of such agglomerates reveals a highly orientated epitaxial inter-relationship between their constituent micro-crystallites. This is found to be consistent with a secondary nucleation growth mechanism associated with re-growth at the 3-fold corner sites within the crystals’ dominant {1 1 0} dodecahedral morphology. The agglomeration appears to heal upon further growth as the aligned agglomerated micro-crystals connect and fuse together but, in doing so, pockets of inter-crystallite mother liquor become trapped forming a symmetric pattern of solvent inclusions. The mechanistic origin of this phenomenon is rationalised with respect to historical data together with an analysis of the solid-state chemistry of the compound through the development of a ‘snow flake’ model. The latter draws upon hexamine's propensity for edge growth instabilities with increasing crystal size as well as its tendency for unstable growth at the facet corners along the 〈1 1 1〉 directions, a situation compounded by the lack of growth-promoting dislocations at the centers of the {1 1 0} habit surfaces. The agglomerative mechanism presented here could apply to other high symmetry crystal systems, particularly those whose crystal structures involve centred Bravais lattices and where the dominant inter-molecular interactions are angled towards the facet edges.
Item Type | Article |
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Uncontrolled Keywords | A1. Computer simulation; A1. Morphological stability; A1. Supersaturated solutions; A1. X-Ray computed tomography; A2. Growth from solutions |
Subjects |
Physics and Astronomy(all) > Condensed Matter Physics Chemistry(all) > Inorganic Chemistry Materials Science(all) > Materials Chemistry |
Date Deposited | 26 Jul 2024 10:25 |
Last Modified | 26 Jul 2024 10:25 |
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Read more research from the creator(s):
- Nguyen, Thai T.H.
- Gajjar, Parmesh
- Sun, Jun
- Hammond, Robert B.
- Murnane, Darragh
- Tordoff, Benjamin
- Lauridsen, Erik
- Withers, Philip J.
- Roberts, Kevin J.
Find work associated with the faculties and division(s):
- Department of Clinical, Pharmaceutical and Biological Science
- School of Life and Medical Sciences
- Airway Group
- Pharmaceutics
- Pharmaceutical Analysis and Product Characterisation
- Centre for Research into Topical Drug Delivery and Toxicology
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