Influence of Endohedral Confinement on the Electronic Interaction between He atoms: A He₂@C₂₀H₂₀Case Study

Abstract

The electronic interaction between confined pairs of He atoms in the C(20)H(20) dodecahedrane cage is analyzed. The He-He distance is only 1.265 A, a separation that is less than half the He-He distance in the free He dimer. The energy difference between the possible isomers is negligible (less than 0.15 kcal mol(-1)), illustrating that there is a nearly free precession movement of the He(2) fragment around its midpoint in the cage. We consider that a study of inclusion complexes, such as the case we have selected and other systems that involve artificially compressed molecular fragments, are useful reference points in testing and extending our understanding of the bonding capabilities of otherwise unreactive or unstable species. A key observation about bonding that emerges uniquely from endohedral (confinement) complexes is that a short internuclear separation does not necessarily imply the existence of a chemical bond.

Bond Paths Are Not Chemical Bonds

“…This paper addresses criticisms that have recently appeared in papers by Grimme et al 1 and Merino et al, 2,3 but the problems addressed here are general.…”

Encapsulation of small gas molecules and rare gas atoms inside the octa acid cavitand

“…The successful incorporation of Rg atoms within the fullerene cages [65] drew significant attention from both theoreticians and experimentalists for further exploration about the systems having endohedrally confined Rg atoms [66][67][68][69][70][71][72][73][74]. Smaller cages like dodecahedrane, adamantane, cubane, BN-cages, other hydrocarbon cages, cucurbit [6] uril, and carbon nanotube were also adopted to encapsulate Rg atoms [68,[70][71][72][73][74]. Though they were found to be thermochemically unstable, they are kinetically stable with respect to the dissociation into the individual cage and Rg atoms.…”

Evaluating common QTAIM and NCI interpretations of the electron density concentration through IQA interaction energies and 1D cross-sections of the electron and deformation density distributions

“…Numerous cases exist, however, where either (i) classical chemists expect a bonding interaction (or it is shown through other methods, such as energy decomposition schemes) but no AIL is present [15], or (ii) steric repulsion is believed to exist, but an AIL is seen regardless [16][17][18][19][20][21][22][23][24][25][26]. These problem cases have resulted in a very long debate, questioning on one hand the validity and interpretation of QTAIM results [27][28][29][30][31] and on the other hand the nature of classical chemical concepts, such as steric repulsion [32][33][34][35][36].…”