DOI: 10.1002/chem.200802596 Bonding or Nonbonding? Description or Explanation? “Confinement Bonding” of He@adamantane Shu-Guang Wang, [a, b] Yi-Xiang Qiu, [a] and W. H. Eugen Schwarz* [a, b] Introduction Explanations and interpretations in the complex field of chemistry are not unique. Different explanations may all be logically consistent. The Table-of-Contents entries of two successive articles in this Journal [8b, 9a] contained declarations of “genuine He  C bonds” and of definitely “no He  C bonds”. If one interpretational view is correct, this does not predetermine complementary views. However, the view- points should be explicitly specified. If some logically cor- rect explanation fits to our ways of thinking, it contributes some facet to our insight. Correspondence relations between different bond analysis schemes and the resolution of some apparent contradictions have recently been investigated by Martín Pendµs et al. [1] Paradoxes also emerge when one does not distinguish between the physical origin of some in- teratomic interaction and the final resulting state of the equilibrium product. A famous example in this respect is the covalent interac- tion between two open-shell fragments. According to Hell- mann [2] and Ruedenberg, [3] the specific origin of covalence is Lewis-type electron sharing by two (or more) atoms. [4] Thereby, the positional uncertainty of the electrons is in- creased. According to Heisenbergs uncertainty principle, the bounds of the momentum uncertainty become lowered with a concomitant reduction of the kinetic energy density. The reduced kinetic energy “pressure” then induces a con- traction of the valence electron density towards the attrac- tive atomic cores. The expectation value of the potential energy between the atomic cores and the valence electrons decreases, while the quantum kinetic energy value of the va- lence shell increases, until the molecular virial theorem [2, 5] is fulfilled. As a result, the covalent bond, as with any kind of bond, is characterized by an increase of the kinetic energy value and a twice as large decrease of the potential energy value. This ubiquitous paradoxical situation is explained and put into a larger context in the Appendix. Another example, presently under hot discussion, is the interaction between closed shells, for example, between ad- jacent bonded hydrogen atoms in biphenyl and phenan- threne, or of noble gas atoms in cage molecules. [6–10] Elec- Abstract: Different insights into chemi- cal phenomena are obtained by analyz- ing the whole process (comparing three or more points, thereby explaining the atomistic mechanism) or only the final product (yielding an interesting finger- print of the result). The viewpoint de- pends 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 frag- ments to molecule. We examine the formation of the inclusion complex He@adamantane. The large antibond- ing energy expense is partitioned into four physical contributions according to chemical concepts. Introduction of the He atom into an undeformed ada- mantane cage leads to a large increase of Pauli repulsion; this is partly moder- ated by electrostatic overlap attraction and by electronic and nuclear relaxa- tions. The IUPAC definition of bonding comprises this antibonding interaction, since a (meta)stable complex is formed. We call it “confinement bond- ing”. 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. Keywords: bond theory · cage com- pounds · noble gases · quantum chemistry · scientific logic [a] S.-G. Wang, Y.-X. Qiu, W. H. E. Schwarz Shanghai Jiao Tong University 800 Dong Chuan Lu, 200240 Shanghai (China) E-mail : schwarz@chemie.uni-siegen.de [b] S.-G. Wang, W. H. E. Schwarz Theoretische Chemie, FB8, Universität Siegen Adolf-Reichwein-Strasse 2–3, 57068 Siegen (Germany) Fax: (+ 49) 271-740-4338  2009 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2009, 15, 6032 – 6040 6032