Design and Synthesis of Pentadentate N3O2-Type Donor Schiff Bases and their Interactive Behavior with UO2(VI) Ion: An Instance of Strange Behavior of Pyridine in a Uranyl (UO22+) Complex

Mononuclear uranyl(VI) Schiff base complexes of formula [UO₂(L₁)]·py (1·py) {[UO₂(L²)]}₂·MeCN·H₂O (2·MeCN·H₂O) have been prepared and characterized by both IR and ¹H NMR spectroscopy and X-ray crystallography. The complex species 1·py crystallizes as orange needle-like crystals in the orthorhombic space group, Pbca, with 8 molecules per unit cell. Interestingly, the pyridine molecule does not participate in coordination to the metal center and was found as a solvent molecule embedded in the crystal structure with weaker interactions to the metal complex. The crystals of the complex species, 2·MeCN·H₂O, crystallized in a monoclinic form, space group, P2₁, with 2 molecules in the asymmetric unit. The two molecules [(UO₂)(L₂)(CH₃CN or H₂O)] in the asymmetric unit of 2·MeCN·H₂O exhibit a competitive (CH₃CN/H₂O) scenario without any direct coordination to the uranyl ion.

Graphical Abstract

Uranyl(VI) Schiff base complexes of general formula [UO₂(L₁)]·py (1·py) and {[UO₂(L²)]}₂·MeCN·H₂O (2·MeCN·H₂O) have been prepared and characterized by spectroscopic analysis and X-ray crystallography.