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Abstract
The chemistry of helium has hitherto been confined to experimental and theoretical analysis of small molecules containing three to five atoms in the gas phase. Here a new suggestion is made for compounds of helium deriving from a recent proposal that five-coordinate carbon might be captured as a frozen SN2 transition state. A series of logical steps, originally discussed as postings and comments to two blogs, led to the outcome described here of a central hypervalent atom bound on one face by a small cyclic carbon ligand, with the other free face having an interaction to a helium atom with the topological properties of a charge-shift rather than a covalent bond. Although high-level theory predicts these helium bonds to be quite short with relatively high stretching frequencies, the kinetic barriers to the loss of helium are predicted to be small, and are not increased by the strategy of having bulky substituents on the ring ligand. Helium is a reluctant participant when it comes to chemical reactions and bonding and it is one of only two stable elements for which there are currently no known crystalline derivatives. Now, based on a computational investigation, compounds containing helium atoms that form charge-shift, rather than covalent bonds have been proposed.Cite this article
Rzepa, H. The rational design of helium bonds. Nature Chem 2, 390–393 (2010). https://doi.org/10.1038/nchem.596 