Acid Mediated In‐Situ Catalytic Cleavage/Making of C=N Bonds in Bis‐Hydrazone Uranyl Complexes: Exploration of Photophysical, Electrochemical, Dye Sorption Properties and DFT Studies

Two new uranium complexes [UO 2 L 2 (H 2 O)] (where L 2 =diacetyl bis‐isonicotinoyl hydrazone) complex 1 , and [UO 2 ( L 1 ) 2 ] (where L 1 =diacetylmonoxime isonicotinoylhydrazone) complex 2 , have been synthesized by precisely adjusting the pH values of the reaction system. Complex 1 was formed in an acidic ethanolic solution (pH=3) through an in‐situ acid catalytic reaction of diacetylmonoxime isonicotinoylhydrazone and UO 2 (NO 3 ) 2 .6H 2 O, while complex 2 was acquired in a neutral medium (pH=7) through self‐assembly of two ligands and one uranium (VI) metal centre. Both complexes were thoroughly characterized by elemental analysis, UV‐Visible spectroscopy, IR spectroscopy, NMR, TGA, cyclic voltammetry, and powder X‐ray diffraction. The studies indicate that the bis‐hydrazone in complex 1 is a dianionic tetradentate N 2 O 2 donor, whereas in complex 2 it is a monoanionic tridendate N 2 O donor. The formation of complex 1 was further confirmed by a single‐crystal X‐ray diffraction study, which revealed the role of a water molecule in forming a pentagonal bipyramidal geometry of [UO 2 L 2 (H 2 O)]. Photophysical studies revealed that complexes 1 and 2 exhibited low band gap values of 2.07 and 2.12 eV, respectively, indicating their semiconducting nature. From the CV measurements, the higher negative potentials of the complexes 1 & 2 { 1 , −0.6 V and 2 , −0.5 V vs. ferrocenium/ferrocene (Fc + /Fc)} in DMSO are assigned to the presence of {UO 2 } 2+ /{UO 2 } + couple signifying their redox active nature. Dye adsorption studies show that both the complexes were able to remove 90 % of Methylene blue (MB) and Rhodamine B (RhB) from the solutions with the concentration of 10 −5 M. The structural insights and electronic properties of Ligand H L 1 and complex 1 were further explored by density functional theory (DFT) calculations.