The Hydrogen Bond and Beyond: Perspectives for Rotational Investigations of Non‐Covalent Interactions

Abstract

In the last decade, experiment and theory have expanded our vision of non‐covalent interactions (NCIs), shifting the focus from the conventional hydrogen bond to new bridging interactions involving a variety of weak donor/acceptor partners. Whereas most experimental data originate from condensed phases, the introduction of broadband (chirped‐pulse) microwave fast‐passage techniques has revolutionized the field of rotational spectroscopy, offering unexplored avenues for high‐resolution studies in the gas phase. We present an outlook of hot topics for rotational investigations on isolated intermolecular clusters generated in supersonic jet expansions. Rotational spectra offer very detailed structural data, easily discriminating the isomeric or isotopic composition and effectively cancelling any solvent, crystal, or matrix bias. The direct comparison with quantum mechanical predictions provides insight into the origin of the inter‐ and intramolecular interactions with much greater precision than any other spectroscopic technique, simultaneously serving as test‐bed for fine‐tuning of theoretical methods. We present recent examples of rotational investigations around three topics: oligomer formation, chiral recognition, and identification of halogen, chalcogen, pnicogen, or tetrel bonds. The selected examples illustrate the benefits of rotational spectroscopy for the structural and energetic assessment of inter‐/intramolecular interactions, which may help to move from fundamental research to applications in supramolecular chemistry and crystal engineering.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

“…33,34 Understanding the changes in electronic structure that occur in the ionic clusters is critical to unveil their structure and function and is important in cloud nucleation in the earth's atmosphere, 35 radiation biology, 36 and catalysis. 37 Furthermore, they can act as model systems for understanding non-covalent interactions 38 and their effects on chemical reactivity, for instance in heterogeneous catalysis, 39 ionic liquids, 40 and aerosol chemistry. 41 We have investigated proton and charge transfer in hydrogen bonded, π-stacked and solvated systems using synchrotron based molecular beams mass spectrometry coupled with electronic structure calculations performed within the group and also with extensive collaborations with Martin Head-Gordon (UC Berkeley) and Anna Krylov (USC).…”

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…In the modified IUPAC periodic table of the elements reported in Figure 1, we noted in black all the NCIs reported up to now and in blue these not yet discussed. A similar representation was used by Caminati et al for the front page of their publication [12]. They called the bonds of the groups MB (2), IB (13), TB (14), NB (15), CB (16), and XB (17) following previous authors.…”

Rotational Spectroscopy Meets Quantum Chemistry for Analyzing Substituent Effects on Non-Covalent Interactions: The Case of the Trifluoroacetophenone-Water Complex

“…Among the possible interactions, hydrogen bond (HB) [6,7] is widespread in nature, frequently playing a fundamental role in life processes, e.g., by tuning nucleobase pairing in DNA and RNA, or in self-assembling processes in functional materials [8], organocatalysis [9] and many other situations. In this respect, HB features can be characterized by quantum-chemical methods [10][11][12] as well as by different spectroscopic techniques, such as the X-ray [13,14], NMR [14,15], IR [14,[16][17][18], Raman [17,18], ZEKE [19], REMPI [19] and microwave (MW) [20,21] spectroscopy. Indeed, the combination of this last technique with supersonic expansion makes it possible to generate stable weakly bound complexes in the gas phase that can be characterized by means of their rotational spectra.…”