Disorder of methyl groups with temperature in two molecular crystals by neutron diffraction

Morris, E. Kaiser; Paulus, Werner; Cousson, A.; Heger, G.

doi:10.1016/s0921-4526(96)00885-x

Cited by 3 publications

(1 citation statement)

References 2 publications

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“…4). The square-like distribution is similar to that reported by Kaiser-Morris et al (1997) for the hydrogenated single crystal at 160 K. This distribution can be rationalized with either coupled rotational and translational motions of the methyl groups (Schiebel et al, 1998) or convolution of the probability density distributions of the disordered methyl groups and of the orientation of the C3-C4 rotational axis (Nicolaï et al, 2003). These models cannot normally be distinguished in diffraction experiments.…”

Section: K Structuresupporting

confidence: 75%

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

Damay¹,

Carretero-Genevrier²,

Cousson³

et al. 2006

Acta Crystallogr Sect B

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The structure of 4-methylpyridine-N-oxide has been determined at 250, 100 and 10 K by combined synchrotron (C(6)H(7)NO) and neutron (C(6)D(7)NO) powder diffraction experiments. At 250 K the space group is I4(1)/amd and the tetragonal unit cell [a = b = 7.941 (2), c = 19.600 (5) A] contains eight equivalent molecules. At 100 K the structure is orthorhombic, with space group Fddd, a = 12.138 (2), b = 10.237 (2) and c = 19.568 (3) A. The 16 equivalent molecules are rotated by about 8 degrees around the c axis with respect to positions at high temperature. At 10 K the best structural model corresponds to a tetragonal unit cell with the space group P4(1), a = b = 15.410 (2) A and c = 19.680 (3) A. The 32 molecules (eight molecules in the asymmetric unit) show complex reorientations around the three cell axes. Whereas at 250 and 100 K the deuterated methyl groups are largely disordered, at 10 K they are ordered in-phase along infinite chains parallel to a and b. Face-to-face methyl groups along c are in an eclipsed configuration. The structure at 10 K suggests that the manifold of rotational tunnelling transitions could be due to inequivalent lattice sites for crystallographically independent methyl groups.

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Section: K Structuresupporting

confidence: 75%

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

Damay¹,

Carretero-Genevrier²,

Cousson³

et al. 2006

Acta Crystallogr Sect B

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Influence of modelling disorder on Hirshfeld atom refinement results of an organo-gold(I) compound

Pawlędzio¹,

Malińska²,

Kleemiss³

et al. 2022

IUCrJ

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Details of the validation of disorder modelling with Hirshfeld atom refinement (HAR) for a previously investigated organo-gold(I) compound are presented here. The impact of refining disorder on HAR results is discussed using an analysis of the differences of dynamic structure factors. These dynamic structure factor differences are calculated from thermally smeared quantum mechanical electron densities based on wavefunctions that include or exclude electron correlation and relativistic effects. When disorder is modelled, the electron densities stem from a weighted superposition of two (or more) different conformers. Here this is shown to impact the relative importance of electron correlation and relativistic effect estimates expressed by the structure factor magnitudes. The role of disorder modelling is also compared with the effect of the treatment of hydrogen anisotropic displacement parameter (ADP) values and atomic anharmonicity of the gold atom. The analysis of ADP values of gold and disordered carbon atoms showed that the effect of disorder significantly altered carbon ADP values and did not influence those of the gold atom.

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Quantitative Atom-Atom Potentials from Rotational Tunneling: Their Extraction and Their Use

Johnson

Kearley

2000

Annu. Rev. Phys. Chem.

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Key Words tunneling, force fields, quantum chemistry, neutron scattering s Abstract Rotational tunneling of small molecular groups has been the subject of considerable theoretical and experimental activity for several decades. Much of this activity has been driven by the promise of exploiting the extreme sensitivity of quantum tunneling to interatomic potentials, but until recently, there was no straightforward means by which quantitative information about these potentials could be extracted. This review explains how a quantitative method, suitable for general application, was developed. It then goes on to show how this has been used to understand tunneling systems for which no previous satisfactory explanation had been found. The application of the methodology, and its results, to other disciplines is discussed.

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Disorder of methyl groups with temperature in two molecular crystals by neutron diffraction

Cited by 3 publications

References 2 publications

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

Influence of modelling disorder on Hirshfeld atom refinement results of an organo-gold(I) compound

Quantitative Atom-Atom Potentials from Rotational Tunneling: Their Extraction and Their Use

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