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.