Structural Characterization and Redox Activity of a Uranyl Dimer and Transition-Metal Complexes of a Tetradentate BIAN Ligand

The synthesis and characterization of a new ligand system combining the redox-active backbone of Ar-BIANs (N,N′-bis[(aryl)imino]acenaphthenes) and a mixed-donor O–N–N–O salen-type binding pocket is reported. Complexes of Co²⁺, Ni²⁺, and UO₂²⁺ were prepared and characterized through single-crystal X-ray diffraction and electrochemical studies. The Ni²⁺ and Co²⁺ complexes have been used as references against which to compare the unique behaviors exhibited by the uranyl (UO₂²⁺) complex, as the latter forms two distinct solid-state structures with unusual oxo contacts to CH₂Cl₂ and CHCl₃ and displays a rich electrochemical profile that indicates a wide range of accessible metal oxidation states through the formation of mixed-valent U(VI)/U(V) and U(V)/U(IV) species in solution.