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Mapping C−H•••M interactions in confined spaces: (α-ICyDᴹᵉ)Au, Ag, Cu complexes reveal “contra-electrostatic H-bonds” masquerading as anagostic interactions

revised on 27.04.2020 and posted on 28.04.2020 by Gabriel dos Passos Gomes, Guangcan Xu, Xiaolei Zhu, Lise-Marie Chamoreau, Yongmin Zhang, Olivia Bistri Aslanoff, Sylvain Roland, Igor Alabugin, Matthieu Sollogoub

What happens when a C−H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as “contra-electrostatic” H-bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H-bonding with an unusual contra-electrostatic component. While electrostatics is strongly stabilizing component in the conventional C−H•••X bonds where X is an electronegative main group element, it is destabilizing in the C−H•••M contacts when M is Au(I), Ag(I), or Cu(I) of NHC−M−Cl systems. Such remarkable C−H•••M interaction became experimentally accessible within (α-ICyDMe)MCl, NHC−Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C−H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set of d-orbitals. A combination of experimental and computational data demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C−H bond to point toward the metal, and reveals a still attractive “contra-electrostatic” H-bonding interaction.


National Science Foundation (Grant CHE-1800329)




Email Address of Submitting Author


Florida State University, Sorbonne Université, University of Toronto


USA, France, Canada

ORCID For Submitting Author


Declaration of Conflict of Interest

We declare no conflict of interests.

Version Notes

Version 1: pre-journal submission. Version 2: pre-journal submission, improved Schemes.