ECA lunchtime webinars - Basic chemical concepts challenged by experimental charge density

L'Association Européenne de Cristallographie (ECA) organise depuis 2021 des "webinaires déjeuner". Les groupes d'intérêt spéciaux (SIG) et les groupes d'intérêt général (GIG) de l'ECA organisent à tour de rôle un webinaire adapté à la communauté des cristallographes au sens large. Le 32ième webinaire sera diffusé le jeudi 5 décembre  2024 à 13h:   Basic chemical concepts challenged by experimental charge density par Dietmar Stalke (University of Göttingen, Allemagne). Inscriptions ici.

 

From the knowledge of the distances at the atomic level and the arrangement in the solid phase many properties, both at the molecular and materials scale, can be deduced. However, the most basic concept, the chemical bond and reactivity, is still vigorously discussed. Still there is room for interpretation, because single crystal structural analyses based on the independent atom model only provides the positions of the centroids of the atoms and the distances between the atoms. In the electron density maps there are no lines or dashes defining or even indicating the chemical bond and the nature of the bonding remains a matter of interpretation based on a bonding model. Hence the anecdote that a bond is where the chemist draws the line remains valid to a certain extent. Most of our understanding of the chemical bond is still deduced from the distances and angles, which are determined as a result of the crystallographic analysis and reactivity is introduced on this basis. Various topics are addressed in the talk and connected to reactivity:

1) Hal∙∙∙Hal bonding in [Cl3]– for safe Cl2 storage and transport. 

2) Chalcogen∙∙∙hydride bonding in Si–H activation.[3]

3) S=N vs. Sδ+–Nδ– bonding and consequences to e. g. single-molecule magnets.[4]