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Detailed Geometric and Electronic Structures of a One-Electron-Oxidized Ni Salophen Complex and Its Amido Derivatives



Square-planar nickel(II) complexes of 1,2-bis(2-hydroxy-3,5-di-tert-butylbenzimino)benzene ([1]), 1-(2-hydroxy-3,5-di-tert-butylbenzimino)-2-(2-hydroxy-3,5-di-tert-butylbenzamido)benzene ([2]) and 1,2-bis(2-hydroxy-3,5-di-tert-butylbenzamido)benzene ([3]2–) were chemically oxidized by one-electron to afford nickel–radical species with non-negligible metal contribution to the singly occupied molecular orbital (SOMO). The X-ray crystal structure of [1][SbF6]shows an almost symmetric metal coordination sphere and phenoxyl pattern within the ligand framework. The spin population at the nickel ion calculated by DFT (B3LYP) does not evolve monotonically within the series, and the values are 18.7, 19.5, and 42.7 % for [1]+, [2], and [3], respectively. Complexes [1]+, [2], and [3] each exhibit a weak near-IR (NIR) band at 3600, 4440, and 5900 cm–1, respectively, the origin of which differs. For [1]+, it corresponds to an intervalence charge transfer (IVCT) transition (β-HOMO → β-LUMO) typical for delocalized compounds (calcd. 3700 cm–1). For [2], which is a localized radical, it is assigned to an intraligand charge transfer (CT) transition (calcd. 5000 cm–1). Although the CT transition still involves orbitals mainly centered on the ligand, it acquires significant ligand-to-metal charge transfer (LMCT) character in the case of [3] (calcd. 5700 cm–1).