Beyond Duality: Rationalizing Repulsive Coulomb Barriers in Host-Guest Cyclodextrin-Dodecaborate Complexes

摘要

Therepulsive Coulomb barrier (RCB), an intrinsic potential energybarrier along electron detachment or charge-separation coordinatesin multiply charged anions (MCAs), provides dynamic stability to MCAswhose electronic and thermodynamic stabilities are largely dictatedby strong internal Coulomb repulsions. Spectroscopic and theoreticalcharacterizations of the RCB have been focused on isolated MCAs. Inthis work, we extend the RCB investigation beyond the previous scopeby including noncovalent host-guest cyclodextrin-closo-dodecaborate dianionic complexes & chi;CD & BULL;B12X12 (2-) (& chi; = & alpha;, & beta;, & gamma;;X = H, F-I). Photodechment photoelectron spectroscopy revealsthe existence of two distinctly different RCBs, derived from detachingelectrons from the guest dianions (RCB1) or ionizing thehost neutrals (RCB2), respectively, with the latter beingsubstantially smaller than the former. Theoretical calculations supportthe duality of RCBs in these complexes and further exhibit highlyanisotropic nature of the RCBs.

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