Thorium(IV) Coordination Polymers in the Pyridine and Pyrazinedicarboxylic Acid Systems

Self-assembly under hydrothermal conditions has been employed to synthesize several novel thorium-containing polymeric materials in the pyridinedicarboxylic acid (pydc) and pyrazinedicarboxylic acid (pzdc) systems. 2,3-, 2,4-, and 2,5-Pyridinedicarboxylic acid along with 2,3-, and 2,5-pyrazinedicarboxylic acid were utilized as organic linkers to produce thorium(IV) coordination polymers. Coordination of the thorium(IV) cations to the ligands in a bidentate fashion through a carboxylate group and either the pyridine or pyrazine ring to form a five-membered ring is a common structural theme throughout all of these compounds. Additionally, this choice of linkers allows for analysis of how the disposition of a second carboxylate group on an aromatic ring affects the overall structural topology. This aforementioned bidentate coordination is observed to vary as the arrangement between the carboxylate groups and N donor sites is optimized. In the pyrazine system, the frequency of this coordination is increased as the carboxylate groups are positioned on opposite sides of the ring while also providing the only form of metal-to-ligand coordination when 2,5-pyrazinedicarboxylic acid is the organic linker (compound 4). Presented are the syntheses, crystal structures, and a crystal-chemical discussion of these thorium-containing compounds.