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Different Nature of the Interactions between Anions and HAT(CN)6: From Reversible Anion−π Complexes to Irreversible Electron-Transfer Processes (HAT(CN)6 = 1,4,5,8,9,12-Hexaazatriphenylene)

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journal contribution
posted on 19.02.2016, 22:01 by Gemma Aragay, Antonio Frontera, Vega Lloveras, José Vidal-Gancedo, Pablo Ballester
We report experimental evidence indicating that the nature of the interaction established between HAT­(CN)6, a well-known strong electron acceptor aromatic compound, with mono- or polyatomic anions switches from the almost exclusive formation of reversible anion−π complexes, featuring a markedly charge transfer (CT) or formal electron-transfer (ET) character, to the quantitative and irreversible net production of the anion radical [HAT­(CN)6]•– and the dianion [HAT­(CN)6]2– species. The preferred mode of interaction is dictated by the electron donor abilities of the interacting anion. Thus, weaker Lewis basic anions such as Br or I are prone to form mainly anion−π complexes. On the contrary, stronger Lewis basic F or OH anions display a net ET process. The ET process can be either thermal or photoinduced depending on the HOMO/LUMO energy difference between the electron donor (anion) and the electron acceptor (HAT­(CN)6). These ET processes possibly involve the intermediacy of anion−π complexes having strong ET character and producing an ion-pair radical complex. We hypothesize that the irreversible dissociation of the pair of radicals forming the solvent-caged complex is caused by the reduced stability (high reactivity) of the radical resulting from the anion.