Quantum Crystallography in the Last Decade: Developments and Outlooks

In this review article, we report on the recent progresses in the field of quantum crystallography that has witnessed a massive increase of production coupled with a broadening of the scope in the last decade. It is shown that the early thoughts about extracting quantum mechanical information from crystallographic experiments are becoming reality, although a century after prediction. While in the past the focus was mainly on electron density and related quantities, the attention is now shifting toward determination of wavefunction from experiments, which enables an exhaustive determination of the quantum mechanical functions and properties of a system. Nonetheless, methods based on electron density modelling have evolved and are nowadays able to reconstruct tiny polarizations of core electrons, coupling charge and spin models, or determining the quantum behaviour at extreme conditions. Far from being routine, these experimental and computational results should be regarded with special attention by scientists for the wealth of information on a system that they actually contain

Pressure stabilization effect on the donor–acceptor polyiodide chains in tetraethylammonium bis(diiodine) triiodide – insights from Raman spectroscopy

: Polyiodides present high bonding flexibility already at ambient conditions, and undergo significant pressure-induced structural deformations. Resonant Raman spectroscopy has been widely used to study I-I bonds in various polyiodides, but it carries a risk of photodecomposition due to the high visible-light absorption of iodine. In this study, tetraethylammonium (bis)diiodine triiodide (TEAI) has been investigated by resonant Raman spectroscopy up to 12.02(3) GPa. The effect of pressure on the intensities and positions of Raman bands has been evaluated and correlated with the interatomic I-I distances derived from high-pressure X-ray diffraction experiments. Pressure was shown to effectively stabilize TEAI against laser-induced photodecomposition, even after a long course of irradiation with the resonant laser light. Examination of a freshly exposed crystal surface revealed that TEAI superficially passivates with the layer of lower polyiodides, which prevents further iodine loss, and shows distinct pressure-induced behaviour

Comments on `Hydrogen bonds in crystalline D-alanine: diffraction and spectroscopic evidence for differences between enantiomers'

The recent paper by Belo, Pereira, Freire, Argyriou, Eckert & Bordallo [(2018), IUCrJ, 5, 6–12] reports observations that may lead one to think of very strong and visible consequences of the parity-violation energy difference between enantiomers of a molecule, namely alanine. If proved, this claim would have an enormous impact for research in structural chemistry. However, alternative, more realistic, explanations of their experiments have not been ruled out by the authors. Moreover, the theoretical calculations carried out to support the hypothesis are unable to differentiate between enantiomers (molecules or crystals). Therefore, the conclusions drawn by Belo et al. (2018) are deemed inappropriate as the data presented do not contain sufficient information to reach such a conclusion

Hydrophobicity and dielectric properties across an isostructural family of MOFs: a duet or a duel?

An isoreticular family of metal-organic frameworks is post-synthetically subjected to polymer grafting. Surface hydrophobicity analysis, adsorption experiments, and impedance spectroscopy characterise the water molecules adsorbed, both on the surface and in the pores, while resolving how molecular mobility is impacted

Modelling the experimental electron density: only the synergy of various approaches can tackle the new challenges

This is an open-access article distributed under the terms of the Creative Commons Attribution Licence.Electron density is a fundamental quantity that enables understanding of the chemical bonding in a molecule or in a solid and the chemical/physical property of a material. Because electrons have a charge and a spin, two kinds of electron densities are available. Moreover, because electron distribution can be described in momentum or in position space, charge and spin density have two definitions and they can be observed through Bragg (for the position space) or Compton (for the momentum space) diffraction experiments, using X-rays (charge density) or polarized neutrons (spin density). In recent years, we have witnessed many advances in this field, stimulated by the increased power of experimental techniques. However, an accurate modelling is still necessary to determine the desired functions from the acquired data. The improved accuracy of measurements and the possibility to combine information from different experimental techniques require even more flexibility of the models. In this short review, we analyse some of the most important topics that have emerged in the recent literature, especially the most thought-provoking at the recent IUCr general meeting in Montreal.PM thanks the Swiss National Science foundation (Project 160157) for financial support. CL and NC are grateful to Universite de Lorraine, Agence Nationale de la recherche and CNRS, for instrumental and financial support. JMG thanks CentraleSupélec, ANR and CNRS for financial support.Peer Reviewe

Topological and electrostatic properties of diclofenac molecule as a non-steroidal anti-inflammatory drug: An experimental and theoretical study

International audienceDiclofenac is a Non-Steroidal Anti-Inflammatory Drug (NSAID), which highly inhibits the lipoxygenase pathways and reduces the formation of leukotriene lipids. In this work, we report on measurements and calculations of the electron density of Diclofenac, obtained from high resolution experimental X-ray diffraction data at 110K and theoretical calculations. The supramolecular structure is dominated by the formation of a dimer through COOH homo-synthon. The analysis of the molecular electron density (by means of quantum theory of atoms in molecules), the electrostatic potential, the crystal packing and intermolecular interactions (through Hirshfeld surface analysis) enables gaining more insight into the nature of the 2 molecule and its ability to interact with other molecules. Furthermore, the topological properties of the dimer interactions in both the crystal phase and human transthyretin protein environment were identified. The electrostatic potential map shows that the high electronegative regions appear around the carboxyl group of the diclofenac molecule in both the crystal and protein environment. This study is complemented by a molecular dynamics simulation of the interaction of diclofenac with transthyretin protein, which enables to test the hypothesis made with the charge density analysis

Ultrafast vibrational response of activated C–D bonds in a chloroform–platinum(II) complex

[Image: see text] The vibrational response of the activated C–D bond in the chloroform complex [Pt(C(6)H(5))(2)(btz-N,N′)·CDCl(3), where btz = 2,2′-bi-5,6-dihydro-4H-1,3-thiazine] is studied by linear and nonlinear two-dimensional infrared (2D-IR) spectroscopy. The change of the C–D stretching vibration of metal-coordinated CDCl(3) relative to the free solvent molecule serves as a measure of the non-classical Pt···D–C interaction strength. The stretching absorption band of the activated C–D bond displays a red shift of 119 cm(–1) relative to uncoordinated CDCl(3), a strong broadening, and an 8-fold enhancement of spectrally integrated absorption. The infrared (IR) absorption and 2D-IR line shapes are governed by spectral diffusion on 200 fs and 2 ps time scales, induced by the fluctuating solvent CDCl(3). The enhanced vibrational absorption and coupling to solvent forces are assigned to the enhanced electric polarizability of the activated C–D bond. Density functional theory calculations show a significant increase of C–D bond polarizability of CDCl(3) upon coordination to the 16 valence electron Pt(II) complex