Bonding or Nonbonding? Description or Explanation? “Confinement Bonding” of He@adamantane

Abstract

Different insights into chemical phenomena are obtained by analyzing the whole process (comparing three or more points, thereby explaining the atomistic mechanism) or only the final product (yielding an interesting fingerprint of the result). The viewpoint depends also on whether one analyzes the wavefunctions according to notions grounded in chemical experience or along physically well-defined formal concepts. Bond energies can only be understood upon comparing both ends of the formation process from fragments to molecule. We examine the formation of the inclusion complex He@adamantane. The large antibonding energy expense is partitioned into four physical contributions according to chemical concepts. Introduction of the He atom into an undeformed adamantane cage leads to a large increase of Pauli repulsion; this is partly moderated by electrostatic overlap attraction and by electronic and nuclear relaxations. The IUPAC definition of bonding comprises this antibonding interaction, since a (meta)stable complex is formed. We call it "confinement bonding". Single-point analyses of the bond-formation product can only yield one-sided characterizations. Any analysis depends on its prescription, which should always be specified in order to avoid controversies based on a mix up of unlike concepts.