The different nature of the interactions between anions and HAT(CN)6: from reversible anion-pi complexes to irreversible electron transfer processes (HAT(CN)6 = 1,4,5,8,9,12-hexaazatriphenylene)

Abstract

[eng] 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.