Crystal Engineering with the Uranyl Cation II. Mixed Aliphatic Carboxylate/Aromatic Pyridyl Coordination Polymers:  Synthesis, Crystal Structures, and Sensitized Luminescence

Eleven novel U(VI)-containing coordination polymers have been synthesized under hydrothermal conditions and characterized via single-crystal X-ray diffraction and fluorescence spectroscopy. These inorganic/organic hybrid materials represent an important advance in the synthesis of polymeric materials in that multiple organic species have been employed in an effort to influence topology and properties. This family of materials is thus the result of a systematic pairing of the uranyl cation, UO22+, with aliphatic dicarboxylates (see part I, this issue) and the dipyridyl species, 4,4‘-dipyridyl and 1,2-bis(4-pyridyl)ethane. This second organic component assumes a number of roles in these structures, including direct coordination, charge balance, and structure direction. Distinction between which role(s) the dipyridyl species will assume appears to be correlated to the size (length) matching between it and the dicarboxylate linker used. Further, polymerization of primary building units (i.e., monomeric uranyl species) to form novel tetrameric secondary building units is observed in four compounds, possibly as a compensation for size differential between the organic species.