Reaction of 1,3,4,6-tetra-O-acetyl-N-(2-hydroxy)-naphthylidene glucosamine (HL(Ac)) with uranyl acetate in ethanol leads to formation of dinuclear [(UO2)(2)(L)(2)] (1). In a second step 1 is quantitatively transferred into the trinuclear oxo-bridged complex [(UO2)(3)(mu(3)-O)(L)(3)](2-) (2(2-)) via deprotonation and coordination of a water molecule. This transformation was followed by NMR and UV/Vis spectroscopy and it proved possible to selectively introduce O-18 into the mu(3)-bridge.