Structure of trihalogenomesitylenes and tunneling of the methyl groups protons

Meinnel, J.; Mani, M.; Cousson, A.; Boudjada, Fahima; Paulus, Werner; Johnson, Mark R.

doi:10.1016/s0301-0104(00)00242-1

Cited by 16 publications

(24 citation statements)

References 18 publications

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“…Among these the C 3h one gives remarkable agreement with neutron diffraction results. 2,25 Furthermore the calculated normal mode frequencies are in good agreement with those observed by spectroscopy ͑INS, IR, and Raman͒. Another crucial observation was that the wide spreading of the PPD maps (30°to 50°) found by neutron diffraction at 14 K is in full agreement with that calculated from the hindering potentials V h deduced from INS spectra.…”

Section: Experimental Structure Of Tribromomesitylene and Comparissupporting

confidence: 75%

“…2 The dimensional changes in the ͑1 0 0͒ planes may be directly related to the changes in vdW radii of the halogen atoms. However, the analysis of the conformation of the Me groups relative to the benzene ring shows several changes with respect to TBM: The C 3h mo- lecular symmetry with one C-H bond eclipsed for each Me group found in TBM has disappeared in TIM.…”

Section: Discussionmentioning

confidence: 99%

“…The crystal structure of TBM has been solved at 14 K by single-crystal neutron diffraction. 2 The molecules retain an almost perfect threefold symmetry C 3h in the crystal, each Me having the same e t conformation. Recent DFT calculations have shown that two conformations are quasi equally probable.…”

Section: Experimental Structure Of Tribromomesitylene and Comparismentioning

confidence: 99%

“…We have chosen 1,3,5-trihalogeno-2,4,6-trimethylbenzenes ͑or trihalogenomesitylenes: THM͒ because of the high symmetry of the substituents position and of the molecular environment in ͑1 0 0͒ planes. [1][2][3] Although one can expect to find a threefold symmetry and three equivalent Me groups for such molecules, inelastic neutron scattering ͑INS͒ experiments 4,6 have shown that the three Me in one molecule of THM are not equivalent insofar as they always present three different tunnelling splittings. Another surprising result is that the largest splittings were found for the triiodomesitylene ͑TIM͒ at 0.113, 0.194, and 0.718 cm Ϫ1 , indicating that the Me are less hindered in this material.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study

Boudjada

Meinnel

Boucekkine

et al. 2002

The Journal of Chemical Physics

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Articles you may be interested inStructural optimization of molecular clusters with density functional theory combined with basin hopping Conformational distribution of a ferroelectric liquid crystal revealed using fingerprint vibrational spectroscopy and the density functional theory Structure and conformation properties of 1-alkyl-3-methylimidazolium halide ionic liquids: A density-functional theory study Investigation of structure of liquid 2,2,2 trifluoroethanol: Neutron diffraction, molecular dynamics, and ab initio quantum chemical study First the conformations of various ortho and di-ortho substituted toluenes calculated by quantum chemistry methods are discussed as well as the hindering potentials deduced from the latter results and those established experimentally by microwaves and fluorescence techniques. It appears that methyl ͑Me͒ groups are much less hindered in di-ortho than in ortho substituted compounds. Then the study of the 1,3,5-triiodo-2,4,6-trimethylbenzene ͑triiodomesitylene or TIM͒ is reported. Density functional theory ͑DFT͒ calculations indicate that two conformations of the TIM molecule have the same formation energies. One has C 3h symmetry, the other with the C s symmetry is obtained from the C 3h by a rotation of 60°for one Me. Experimentally, the TIM structure has been determined at 15 K using single-crystal neutron diffraction data. TIM crystallizes in the triclinic space group P Ϫ1. Molecules are stacked in an antiferroelectric manner along the oblique a axis. For two Me groups the experimental conformation is close to the C s one, but the third Me group has a C-H bond nearly orthogonal to the ring plane. Such conformation is unstable in the gas state, but it is stabilized in the crystal by intermolecular interactions, nevertheless DFT predicts accurate bond lengths and angles when the Me conformations are constrained to the experimental ones. The three Me groups, having different environments, experience different hindering potentials, this explains why they are tunnelling at different energies as found by inelastic neutron scattering ͑INS͒. Using INS results, we deduced the potentials hindering the Me groups rotation in the crystal. The proton probability densities ͑PPD͒ calculated from these potentials are in concordance with the crystallographic results. Hence the quantum origin of the broad spreading of PPD observed at 15 K is established. Moreover, it is demonstrated that the crystal field is responsible for the larger part of the potentials hindering the Me groups in the solid state.

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Section: Experimental Structure Of Tribromomesitylene and Comparissupporting

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Section: Experimental Structure Of Tribromomesitylene and Comparismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study

Boudjada

Meinnel

Boucekkine

et al. 2002

The Journal of Chemical Physics

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“…By using single crystal experiments methyl groups were assigned to tunneling frequencies in, e.g., 2,6-dimethylpyrazine 2,23 or tribromomesitylene. 24 An assignment of CH 3 groups to tunneling frequencies using a powder sample is possible if the crystal structure is known and the dynamics can be modeled by, e.g., using harmonic approximation in combination with transferable pair potentials or ab initio and molecular-mechanics calculations in reasonable agreement with the experiment.…”

Section: Assignmentmentioning

confidence: 99%

Rotational dynamics of methyl groups in m-xylene

Kirstein¹,

Prager²,

Dimeo³

et al. 2004

The Journal of Chemical Physics

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Methyl group dynamics of m-xylene was investigated by using incoherent inelastic and quasi-elastic neutron scattering. Inelastic measurements were carried out at the high flux backscattering spectrometer HFBS at the National Institute of Standards, quasi-elastic measurements at the time-of-flight spectrometer NEAT at the Hahn-Meitner-Institute. Rotational potentials are derived which describe the tunnel splittings, first librational, and activation energies of the two inequivalent CH 3 groups. Indications for coupling of the methyl rotation to low-energy phonons have been found. The finite width of one tunneling transition at He temperature is described by direct methylmethyl coupling. The combined results of the experiments and the calculations allow a unique assignment of rotor excitations to crystallographic sites.

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Competing stacking modes in crystals of trihalogeno-trimethyl-benzene: Theory meets experiment

Meinnel

Amar

Boucekkine

et al. 2019

Journal of Crystal Growth

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The special case of the stacking of trihalogeno mesitylene (TXM) molecules has been investigated. Below 300 K, these molecules lead to needle shaped crystals in a triclinic arrangement. Thanks to DFT computations and an empirical atom-atom interaction model this packing mode has been rationalized. Aggregates of TXM molecules differently packed have been considered, namely dimers and trimers of type A, the molecules being piled one over the other along the axis a, and dimers B and trimers B, the molecules lying in the same bc plane. From the computations, it appears that the stabilizing energy of formation of a dimer of two molecules piled along a is several times larger than the energy gain obtained from the formation of a dimer of two neighbors in the bc plane. It has also been found that the energy of formation of a trimer of type A is approximately twice the energy of formation of a dimer A, so that an additive rule occurs. These conclusions are in perfect agreement with the experimental observations of the shape of the crystals obtained by crystallization from a super-saturated solution of TXM in an organic solvent: long needles with TXM molecules stacked along the axis a have always been obtained and never thin plate-like crystals.

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Structure of trihalogenomesitylenes and tunneling of the methyl groups protons

Cited by 16 publications

References 18 publications

Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study

Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study

Rotational dynamics of methyl groups in m-xylene

Competing stacking modes in crystals of trihalogeno-trimethyl-benzene: Theory meets experiment

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