Uranyl peroxide clusters stabilized by dicarboxylate ligands : a pentagonal ring and a dimer with extensive uranyl-cation interactions

Great effort has been made to synthesize larger uranyl peroxide clusters whilst the understanding of the basic construction units for these clusters still needs to be further explored. Two small uranyl peroxide clusters stabilized by simple dicarboxylate ligands have been synthesized and characterized. Na10[(UO2) (O2)(C3H2O4)]5_20H2O (1) has a pentagonal ring stabilized by malonate and [Na4K2(UO2)2(O2)(C2O4)4] .6H2O (2) has a dimer stabilized by oxalate. Cation-cation interactions between uranyl and alkali metal ions exist in both 1 and 2, leading to the observation of elongated U=O-yl bonds. Vibrational modes of uranyl ion, peroxide and malonate/oxalate ligands have been confirmed by Raman spectroscopy. The presence of malonate ligands prevents the pentagonal uranyl peroxide rings further assembling into larger clusters whilst the excess oxalate ligands inhibit the dimers further linking to nearby uranyl centers.