Optical transforms of disordered molecular crystals

Welberry, T. R.; Jones, R. D. G.

doi:10.1107/s0021889880012009

Cited by 19 publications

(20 citation statements)

References 3 publications

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“…This has been confirmed by two independent methods and is not an artifact of the refinement procedure. The X-ray diffuse scattering studies to be reported later (Welberry, 1980) show that, in addition to the preferred site occupancy determined here, the orientations of neighbouring molecules related by the statistical centre of symmetry are additionally correlated. In this way, we find that the Br/Me sites which are 6.2/k apart (see Fig.…”

Section: Discussionsupporting

confidence: 60%

Crystals exhibiting disorder – the monoclinic polymorph of 9-bromo-10-methylanthracene

Jones¹,

Welberry²

1980

Acta Crystallogr Sect B

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The crystal structure of C ~sHI1Br has been determined from X-ray (Mo Ka radiation) and neutron (2 ---0.988 /k) diffraction data. The compound crystallizes in the monoclinic space group P2~./c with a = 8.307 (1), b = 9.844 (1), c = 13.815 (2) A, fl = 95.96 (1) °, Z = 4. Refinement led to R and wR values of0-101 and 0.045 for 2197 X-ray reflexions (0-047 and 0-042 for reflexions with I > 2-3oi) and 0.167 and 0.056 for 2299 neutron reflexions (0.059 and 0.046). The 9,10-substituents show disorder of Br and CH 3, the 9-substituent occupied on average by 0.643 Br and 0.357 C and vice versa for the 10-substituent. Additionally, the neutron data show two orientations for the H atoms ofthe CH a.

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Section: Discussionsupporting

confidence: 60%

Crystals exhibiting disorder – the monoclinic polymorph of 9-bromo-10-methylanthracene

Jones¹,

Welberry²

1980

Acta Crystallogr Sect B

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“…Multiple z-matrices were used, though they are essentially the same matrix with the CH 3 and Cl transposed. It has been shown that in CMA the two species (or flipped versions of the one species) occur in the ratio ∼69 : 31 [28][29][30].…”

Section: Preliminary Calculationsmentioning

confidence: 99%

A Process for Modelling Diffuse Scattering from Disordered Molecular Crystals, Illustrated by Application to Monoclinic 9-Chloro-10-methylanthracene

Goossens

2015

Advances in Condensed Matter Physics

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Diffuse scattering from a crystal contains valuable information about the two-body correlations (related to the nanoscale order) in the material. Despite years of development, the detailed analysis of single crystal diffuse scattering (SCDS) has yet to become part of the everyday toolbox of the structural scientist. Recent decades have seen the pair distribution function approach to diffuse scattering (in fact, total scattering) from powders become a relatively routine tool. However, analysing the detailed, complex, and often highly anisotropic three-dimensional distribution of SCDS remains valuable yet rare because there is no routine method for undertaking the analysis. At present, analysis requires significant investment of time to develop specialist expertise, which means that the analysis of diffuse scattering, which has much to offer, is not incorporated thorough studies of many compounds even though it has the potential to be a very useful adjunct to existing techniques. This article endeavours to outline in some detail how the diffuse scattering from a molecular crystal can be modelled relatively quickly and largely using existing software tools. It is hoped this will provide a template for other studies. To enable this, the entire simulation is included as deposited material.

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“…Although it was necessary to use different crystals for each mounting and individual sections were recorded at various times over a period of several months, spherical solutiongrown (from PE) crystals of -0.5 mm diameter were used in each case. To aid in preliminary investigations and for later reference, these photographs were digitized and the data processed in the manner described by Welberry & Jones (1980) to produce the undistorted views of each reciprocal section which are shown in Fig. 2.…”

Section: Data Collectionmentioning

confidence: 99%

Analysis of the diffuse scattering from disordered molecular crystals: application to 1,3-dibromo-2,5-diethyl-4,6-dimethylbenzene at 295 K

Welberry¹,

Siripitayananon²

1987

Acta Crystallogr Sect B

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The disorder diffuse X-ray scattering (DDS) in 1,3-dibromo-2,5-diethyl-4,6-dimethylbenzene, Ct2H16Br2 (BEMB2), has been analysed using the least-squares procedure of Epstein & Welberry [Acta Cryst. (1983), A39, 882-892]. Data from seven reciprocal-lattice sections were used to obtain values for all intermolecular correlation coefficients within a 20/~ neighbourhood. Of the 42 correlations within this neighbourhood, 22 were found to be significantly different from zero, and of these 13 were significant at the 30, level. The largest correlation of 0.21 was between a central molecule and the nearest neighbour in the [100] crystal direction. The five largest correlations were all of opposite sign to the corresponding correlations in the previously reported isostructural BEMB1 [Welberry & Siripitayananon (1986). Acta Cryst. B42, 262-272]. As for BEMB1, the observed correlations do not fully support a previously held theory that the short-range order occurs in such a way as to reduce the number of Br-Br intermolecular contacts in favour of CH3-Br contacts. An unusual diffraction effect in which the diffuse scattering shows a deep depression of intensity close to the (010) reciprocal position has been observed. The origins of this feature, which is considered to arise from an analogous effect to the 'space-group absences' of conventional Bragg-peak data, are discussed.

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Optical transforms of disordered molecular crystals

Cited by 19 publications

References 3 publications

Crystals exhibiting disorder – the monoclinic polymorph of 9-bromo-10-methylanthracene

Crystals exhibiting disorder – the monoclinic polymorph of 9-bromo-10-methylanthracene

A Process for Modelling Diffuse Scattering from Disordered Molecular Crystals, Illustrated by Application to Monoclinic 9-Chloro-10-methylanthracene

Analysis of the diffuse scattering from disordered molecular crystals: application to 1,3-dibromo-2,5-diethyl-4,6-dimethylbenzene at 295 K

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