Chemical bonding in very tight places


Roald Hoffmann,, Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853-1301
Diamond anvil cell and shock–wave technologies now permit the study of matter under multimegabar (i.e. several hundreds GPa) pressures. The properties of molecules and extended structures in this pressure regime differ drastically from those known at 1 atm. Just how different chemistry is at high pressure and the role that a chemical intuition for bonding and structure can have in understanding matter at high pressures will be explored in this lecture. I will discuss in detail an overlapping hierarchy of responses to increased density, consisting of (a) squeezing out van der Waals space (for molecular crystals); (b) increasing coordination; (c) decreasing the bond length of covalent bonds and the size of anions; and (d) an extreme regime of electrons moving off atoms and new modes of correlation. This work is a joint project with Wojciech Grochala, Ji Feng and Neil Ashcroft.