Novel syntheses of carbazole-3,6-dicarboxylate ligands and their utilization for porous coordination cages

The molecular nature, and thus potential solubility, of coordination cages endows them with a number of advantages as compared to metal-organic frameworks and other extended network solids. However, their lack of three-dimensional connectivity typically limits their thermal stability as inter-cage interactions in these materials are relatively weak. This is particularly the case for carbazole-based coordination cages. Here, we report the design and synthesis of a benzyl-functionalized octahedral coordination cage that displays moderate surface area and increased thermal stability as compared to its unfunctionalized counterpart. Structural analysis suggests the increased thermal stability is a result of aryl-aryl interactions between ligand groups on adjacent cages. We have further adapted the ligand synthesis strategy to afford a novel, high-yielding preparatory route for the isolation of carbazole-3,6-dicarboxylic acid that does not rely on pyrophoric reagents or transition metal catalysts. A benzyl-protecting strategy affords access to large quantities of carbazole-based ligands or molecular adsorbents with tunable inter-cage interactions.