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.