ESR Study of High Spin States Derived from Tribenzoylenebenzene

Abstract

By reduction of tribenzoylenebenzene 4 with lithium in 2-methyltetra-hydrofuran (MTHF) an ion pair and a cluster with S = 1 were obtained whereas with potassium or sodium in MTHF in the presence of dicyclohexano-18-crown-6 (or a solvent of strong solvating power such as diglyme or hexamethyl-phosphoric triamide), different species with S ⩾ 1/2 were detected. The ESR spectra of the randomly oriented pluri-anions in glassy matrix showed the existence of triplet species assigned to a dianion [42(.−)(M+)2] and aggregates [4.−(M+)n4.−] and quartet species [42(−)(M+)34.−]. The quartet species was attributed to intermolecular high-spin clusters with the relatively small zero-field splitting parameter D and vanishing E value. Further reduction led to the formation of a more persistent species with a quartet ground state characterized by the zero-field parameters D = + 0.0215 cm−1 and E = 0 cm−1, assigned to a triradical-trianion [43(.−)(M+)3], generated by three-electron doping per a single tribenzoylenebenzene molecule. The observed 1H-ENDOR spectra and INDO calculations also confirmed the above identification. 43(.−) is a stable pluri-anionic high-spin molecule in solution.