Crystal Engineering with the Uranyl Cation Ill. Mixed Aliphatic Dicarboxylate/Aromatic Dipyridyl Coordination Polymers: Synthesis, Structures, and Speciation

Seven novel U(VI)-bearing compounds have been synthesized using hydrothermal conditions and characterized via single crystal X-ray diffraction. These materials are the result of systematically pairing aliphatic dicarboxylic acids and dipyridyl (1,2-bis(4-pyridyl)ethane and trans-1,2-bis(4-pyridyl)ethylene) molecules with the uranyl cation and are a conclusion to parts I and II of this study. A common factor of this family of materials is that the carboxylate group preferentially coordinates to the uranyl center, whereas the dipyridyl plays one of two roles: space filling or direct coordination uranyl cation. The role of the dipyridyl appears to be directly related not only to the length of the aliphatic dicarboxylate with which it is paired but also to the rigidity of the clipyridyl species. Further, this family of materials shows a tendency toward specific primary and secondary building units formed by the oligomerization of the uranyl cation despite suggested by other studies. This tendency appears to be due to the affinity of the ligand(s) for smaller building units.