Uranyl nitrate reacts with citric (H(4)cit) or D-(-)-citramalic (H(3)citml) acids under mild hydrothermal conditions and in the presence of diamines to give different complexes which are all characterized by the presence of 2:2 uranyl/polycarboxylate dianionic dimers or of polymeric chains based on the same dimeric motif. Each uranium ion is chelated by the two ligands through the alkoxide and the alpha- or beta-carboxylate groups, the second beta-carboxylic group in citrate being uncoordinated. The uranium coordination sphere is completed by either a water molecule or the beta-carboxylate group of a neighboring unit, thus giving zero- or one-dimensional assemblages, respectively. The evidence for [UO2(Hcit)](2) dimers in the solid state confirms previous results from potentiometric and EXAFS measurements on solutions. Depending on the diamine used (DABCO, 2,2'- and 4,4'-bipyridine, [2.2.2]cryptand) and its ability to form divergent hydrogen bonds or not, different uranyl/polycarboxylate topologies are obtained, thus evidencing template effects, and extended hydrogen bonding gives two- or three-dimensional assemblages. These results, together with those previously obtained with NaOH as a base, add to the knowledge of the uranyl/citrate system, which is much investigated for its environmental relevance.