X-ray diffuse scattering from HTMA: analysis via a Monte Carlo model
Date
2008
Authors
Goossens, Darren
Heerdegen, Aidan
Welberry, Thomas
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Munksgaard International Publishers
Abstract
Hexamethylenetetramine (HMT, C6H12N4, also referred to as urotropin) and azelaic acid [A, HOOC - (CH2) 7 - COOH] form a co-crystal or adduct (HMTA, also referred to as urotropin azelate) which exhibits several structural phases as a function of temperature. At room temperature, the structure is orthorhombic, but shows substantial disorder. Here, this disorder is explored by analyzing the diffuse scattering from single crystals of HMTA via Monte Carlo simulation. The disorder is in part occupational, with two orientations of azelaic acid occurring, and in part thermally induced, which is to say dynamic. The occupational disorder can be thought of as a combination of limited-range in-plane (bc plane) negative correlations combined with effectively zero correlation between planes (along a), rather like stacking faults. Size effect, the cross-correlation between molecular orientation and displacement from average position, is required to reproduce the observed diffuse scattering.
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Keywords
Keywords: Hexamethylenetetramine (HMTA); Monte Carlo modelling; X ray diffuse scattering Diffuse scattering; Disorder; Monte Carlo model
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Source
Acta Crystallographica Section B: Structural Science
Type
Journal article
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2037-12-31
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