Saccharified uranyl ions. Self-assembly of UO${}_2$${}^{2+}$ into trinuclear anionic complexes by the coordination of glucosamine-derived Schiff bases

The reaction of UO${}_2$(OAc)${}_2$ ⋅ 2H${}_2$O with the biologically inspired ligand 2-salicylidene glucosamine (H${}_2$L${}^1$) results in the formation of the anionic trinuclear uranyl complex [(UO${}_2$)${}_3$(µ${}_3$-O)(L${}^1$)${}_3$]${}^{2-}$ (1${}^{2-}$), which was isolated in good yield as its Cs-salt, [Cs]${}_2$1. Recrystallization of [Cs]${}_2$1 in the presence of 18-crown-6 led to formation of a neutral ion pair of type [M(18-crown-6)]${}_2$1, which was also obtained for the alkali metal ions Rb${}^{+}$ and K${}^{+}$ (M=Cs, Rb, K). The related ligand, 2-(2-hydroxy-1-naphthylidene) glucosamine (H${}_2$L${}^2$) in a similar procedure with Cs${}^{+}$ gave the corresponding complex [Cs(18-crown-6)]${}_2$[(UO${}_2$)${}_3$(µ${}_3$-O)(L${}^2$)${}_3$ ([Cs(18-crown-6)]/${}_2$2). From X-ray investigations, the [(UO${}_2$)${}_3$O(L${}^n$)${}_3$]${}^{2-}$ anion (n=1, 2) in each complex is a discrete trinuclear uranyl species that coordinates to the alkali metal ion via three uranyl oxygen atoms. The coordination behavior of H${}_2$L${}^1$ and H${}_2$L${}^2$ towards UO${}_2$${}^{2+}$ was investigated by NMR, UV/Vis spectroscopy and mass spectrometry, revealing the in situ formation of the 1${}^{2-}$ and 2${}^{2-}$ dianions in solution. (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH)