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

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^-)(I₂P^2-)M, [(I₂P^2-)₂M]^-, and [(I₂P^2-)(I₂P^3-)M]^2-, and for M = Al only, [(I₂P^3-)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^-)(I₂P^2-)M and [(I₂P^2-)(I₂P^3-)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 [(I₂P^2-)(I₂P^3-)M]^2- and class III for M = Al and Ga in (I₂P^-)(I₂P^2-)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.