Homometallic Uranium(VI) Phosphonoacetates Containing Interlayer Dipyridines

Three organically templated uranium(VI) carboxyphosphonates, [C10H10N2][(UO2)3(PPA)2(HPPA)(H2O)]·3H2O (1), [C12H12N2][(UO2)3(PPA)2(HPPA)(H2O)]·2H2O (2), and [C12H14N2][(UO2)3(PPA)2(HPPA)(H2O)]·2H2O (3) have been prepared from hydrothermal reactions of UO2(NO3)2·6H2O and phosphonoacetic acid (H2O3PCH2CO2H, H3PPA) in the presence of 4,4′-dipyridyl, 1,2-bis(4-pyridyl)-ethylene and 1,2-bis(4-pyridyl)-ethane. The crystal structures of 1−3 are built from UO7 units linked via phosphonoacetate molecules to form 2-dimensional [(UO2)3(PPA)2(HPPA)(H2O)]2− networks which are charge balanced by doubly protonated bipyridyl molecules. Interaction of the pyridyl molecules with other functionalities present in 1−3 result in relatively strong N−H···O (2.707−3.155 Å) and weaker C−H···O (2.948−3.237 Å) interactions that constitute the interlayer. Water-carboxylate O−H···O hydrogen bonding (2.548−2.675 Å) in 1−3 and π−π interactions (3.708 Å) between pyridyl rings in 2 also exist in these materials. Reported herein are the syntheses, structural characterization, and thermal and fluorescent behavior of 1−3.