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Organic Electron Delocalization Modulated by Ligand Charge States in [L2M]n– Complexes of Group 13 Ions

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posted on 25.09.2019, 17:44 authored by Amela Arnold, Tobias J. Sherbow, Richard I. Sayler, R. David Britt, Emily J. Thompson, M. Teresa Muñoz, James C. Fettinger, Louise A. Berben
Water-stable organic mixed valence (MV) compounds have been prepared by the reaction of reduced bis­(imino)­pyridine ligands (I2P) with the trichloride salts of Al, Ga, and In. The coordination of two tridentate ligands to each ion affords octahedral complexes that are accessible with five ligand charge states: [(I2P0)­(I2P)­M]2+, [(I2P)2M]+, (I2P)­(I2P2–)­M, [(I2P2–)2M], and [(I2P2–)­(I2P3–)­M]2–, and for M = Al only, [(I2P3–)2M]3–. In solid-state structures, the anionic members of the redox series are stabilized by the intercalation of Na+ cations within the ligands. The MV members of the redox series, (I2P)­(I2P2–)­M and [(I2P2–)­(I2P3–)­M]2–, show characteristic intervalence transitions, in the near-infrared regions between 6800–7400 and 7800–9000 cm–1, respectively. Cyclic voltammetry (CV), NIR spectroscopic, and X-ray structural studies support the assignment of class II for compounds [(I2P2–)­(I2P3–)­M]2– and class III for M = Al and Ga in (I2P)­(I2P2–)­M. All compounds containing a singly reduced I2P ligand exhibit a sharp, low-energy transition in the 5100–5600 cm–1 region that corresponds to a π*−π* transition. CV studies demonstrate that the electron-transfer events in each of the redox series, Al, Ga, and In, span 2.2, 1.4, and 1.2 V, respectively.