One‐ and two‐electron oxidized CuII complexes of Schiff base ligands with para‐substituted phenolate moieties were synthesized and characterized. The crystal structure of the one‐electron oxidized methylthio‐substituted complex [Cu(MeS‐salen)]SbCl6 revealed the intermolecular π‐π stacking interaction of the two phenolate moieties with those of the neighboring complex cations to form the one‐dimensional chain. Such a π‐π stacking interaction could not be detected in the two‐electron oxidized complex [Cu(MeS‐salen)](SbCl6)2 and the oxidized methoxy‐substituted complexes [Cu(MeO‐salen)](SbF6)n (n=1, 2). Magnetic study of [Cu(MeO‐salen)]SbF6 showed a weak antiferromagnetic interaction between the CuII ion and phenoxyl radical unpaired electron spins, while [Cu(MeS‐salen)]SbCl6 showed a ferromagnetism. Both of the two‐electron oxidized complexes exhibited a relatively strong magnetic interaction between the two radical electrons, while the signs of the electron spins are different.

Uranyl(VI) complexes with pentadentate N 3 O 2 -donating Schiff base ligands having various substituents at the ortho (R 1 ) and/or para (R 2 ) positions on phenolate moieties, R 1 ,R 2 -Me saldien 2− , were synthesized and thoroughly characterized by 1 H nuclear magnetic resonance, infrared, elemental analysis, and single-crystal X-ray diffraction. Molecular structures of UO 2 (R 1 ,R 2 -Me saldien) are more or less affected by the electron-donating or -withdrawing nature of the substituents. The redox behavior of all UO 2 (R 1 ,R 2 -Me saldien) complexes was investigated to understand how substituents introduced onto the ligand affect the redox behavior of these uranyl(VI) complexes. As a result, the redox potentials of UO 2 (R 1 ,R 2 -Me saldien) in dimethyl sulfoxide increased from −1.590 to −1.213 V with an increase in the electron-withdrawing nature of the substituents at the R 1 and R 2 positions. The spectroelectrochemical measurements and theoretical calculation [density functional theory (DFT) and timedependent DFT calculations] revealed that the center U 6+ of each UO 2 (R 1 ,R 2 -Me saldien) complex undergoes one-electron reduction to afford the corresponding uranyl(V) complex, [UO 2 (R 1 ,R 2 -Me saldien)] − , regardless of the difference in the substituents. Consequently, the redox active center of uranyl(VI) complexes seems not to be governed by the redox potentials but to be determined by whether the LUMO is centered on a U 5f orbital or on one π* orbital of a surrounding ligand.

No abstract

The U–X bond strength and thermodynamic stability of uranyl(vi) complexes with pentadentate N2O2X1-donating ligands (X = NH, O, S) are affected by the difference in X. In contrast, the X atom does not largely affect the redox behavior of the complexes.

In most cases, redox activity of a UVIO22+ complex is regarded as metal-centered phenomena, because uranium has small energy gaps amongst 5f/6d/7s subshells thereby exhibiting a wide range of oxidation...