Controlling the Structure of Reactive Intermediates via Incipient Covalent Bonding with the Counterions: Coexistence of Two Distinct Forms of the C6F6 Cation Radical in a Single Crystal

Abstract

A number of highly reactive charged intermediates have been stabilized by crystallization with appropriate counterions and cocrystallization partners. Here, we computationally address a recent unexplained observation of the two Jahn–Teller forms of the otherwise unstable C6F6 cation radical in a single crystal with supposedly noncoordinating Sb2F11– counteranions. However, our density functional calculations and the natural bond orbital based analysis techniques clearly demonstrate that the specific charge-transfer interactions with close-contact fluorine atoms of the Sb2F11– counteranions are responsible for the selective stabilization of the bisallyl and quinoidal forms of the C6F6+• cation radical in different counteranion environments. Similar donor–acceptor interactions are also responsible for the much debated stabilization of the crystalline Et3Si+/toluene complex. This paradigm of charge-transfer control of the chemical nature of the crystallized molecules may hold potential for design of the next-generation materials.