A Series of An^VIO₂²⁺ Complexes (An = U, Np, Pu) with N₃O₂-Donating Schiff-Base Ligands: Systematic Trends in the...

In their + V and + VI oxidation states, actinide elements (U, Np, and Pu) are commonly encountered in characteristic linear dioxo structures, known as actinyl ions (AnO₂⁺; An = U, Np, Pu, n = 1, 2). A systematic understanding of the structural and redox behavior of An^VO₂⁺/An^VIO₂²⁺ complexes is expected to provide valuable information for controlling the behavior of An elements in natural environments and in nuclear fuel cycles while enabling the development of spintronics and new reactivities that utilize the anisotropic spin of the 5f electrons. However, systematic trends in the behavior of An^VO₂⁺/An^VIO₂²⁺ complexes remain poorly understood. The [An^V/VIO₂(saldien)]^-/0 complexes (saldien^2- = N,N'-disalicylidenediethylenetriamine) studied here offer a promising avenue for advancing our understanding of this subject. The molecular structures of a series of [An^VIO₂(saldien)] complexes were found to exhibit notable similarities through these An elements with minor, but still significant, contributions from the actinide contraction. The redox potentials of the [An^V/VIO₂(saldien)]^-/0 couples clearly increase from U to Np, followed by a subsequent decrease from Np to Pu (-1.667 V vs Fc^0/+ for [U^V/VIO₂(saldien)]^-/0, -0.650 V for [Np^V/VIO₂(saldien)]^-/0 and -0.698 V for [Pu^V/VIO₂(saldien)]^-/0). Such a difference can be explained in terms of the difference in character of the electronic configuration of the + VI oxidation state. A series of these redox trends was also successfully reproduced by DFT-based calculations. These findings provide valuable information for controlling the oxidation states of the An elements.