16: On the Nature of Hydrogen–Hydrogen Bonding^†

This chapter reviews the recent experimental and computational evidence that support the concept of “hydrogen–hydrogen (or H–H) bonding” which involves the interaction of two neutral hydrogen atoms or two hydrogen atoms bearing charges of the same sign, as a new class of weak interactions. The H–H bonding interaction gains importance due to its utility in rationalizing the stability of several systems where no other attractive interactions are involved such as crystalline structures of n-alkanes and polyhedranes. H–H bonding complements the list of long-known interactions that stabilize the structures of proteins and other macromolecules such as hydrogen-bonding and van der Waals interactions that play a crucial role in the description of chemical structural, stability, and reactivity. The elucidation of this weak interaction from the standpoint of the Quantum Theory of Atoms in Molecules (QTAIM) leads to a quantitative description that is testable by experiment, and provides new insight that broadens and expands our understanding of weak interactions, ubiquitous as they are in nature.