Functionalized Aromatic Dicarboxylate Ligands in Uranyl-Organic Assemblies: The Cases of Carboxycinnamate and 1,2-/1,3-Phenylenedioxydiacetate.

2-Carboxycinnamic acid (ccnH) and the isomeric 1,2- and 1,3-phenylenedioxydiacetic acids (1,2- and 1,3-pddaH) have been used to synthesize eight uranyl ion complexes under solvo-hydrothermal conditions. In the four complexes [PPh][UO(ccn)(NO)] (), [PPh][UO(ccn)(dibf)] (), [UO(ccn)(bipy)] (), and [Ni(,-Mecyclam)][UO(ccn)(HCOO)] (), the ccn dianion retains a nearly planar geometry, which favors the formation of the centrosymmetric [UO(ccn)] dimeric unit. Additional terminal ligands, either neutral (bipy = 2,2'-bipyridine) or anionic (nitrate, dibf = 1,3-dihydro-3-oxo-1-isobenzofuranacetate, and formate, the two latter formed in situ), complete the uranyl coordination sphere, leading in all cases to discrete, dinuclear species. Sodium(I) bonding to the carboxylate/ether O site of the 1,2-pdda dianion in the two complexes [UONa(1,2-pdda)(OH)] () and [(UO)Na(1,2-pdda)(CO)] () results in this ligand being planar. Further lateral coordination to uranyl and sodium bonding to a uranyl oxo group allow formation of heterometallic diperiodic networks containing monoperiodic uranyl-only subunits. In the absence of Na cations, 1,2-pdda adopts a conformation in which one carboxylate group is tilted out of the ligand plane in [UO(1,2-pdda)Ni(cyclam)] () and diaxial carboxylato bonding to nickel(II) unites uranyl-only monoperiodic subunits into a diperiodic network. The 1,3-pdda ligand in [UO(1,3-pdda)(HO)] () is also nonplanar with one tilted carboxylate group, and the bridging bidentate nature of both carboxylate groups allows formation of a triperiodic framework in which both metal and ligand are four-coordinated nodes. While the emission spectra of complexes and display the vibronic progression considered typical of uranyl ion, those of complexes , , and show broad emission bands which in the case of complex completely replace the uranyl emission and which appear to be ligand-centered. The low energy of these broad bands can be rationalized in terms of the close association of certain ligand pairs within the structures.