Thermal stability of coordination polymers

Polymers formed between three ligands and selected metal ions were prepared and their thermal stability in air was investigated. 1,5-Dihydroxynaphthalene-2,6-dicarboxylic acid (1,5-N-2,6) formed coordination polymers with Zn, Ni, Al, and Fe+3. Zn-1,5-N-2,6 was more stable than the corresponding Fe and Ni polymers. Pyromellitic acid (PMA) formed coordination polymers of high molecular weight with Th and U+4. The Th-PMA was stable up to 405°C., while the corresponding uranium compound decomposed below 400°C. The coordination polymer of 2,3,6,7-naphthalenetetracarboxylic acid (NT) with Th was less stable (decomposition temperature: 360°C.) than the corresponding pyromellitic polymer because the coordination of Th in Th-NT was partially accomplished by water molecules rather than carboxylic oxygens as in the Th-PMA polymer. The thermal stability of these polymers was a function of the metal involved in coordination. Higher thermal stability resulted when Zn or Th were used than if metals capable of changing their ionic valency were involved in polymer formation.