Carboxylic Acid and Phenolic Hydroxyl Interactions in the Crystal Structures of Co-Crystals/Clathrates of Trimesic Acid and Pyromellitic Acid with Phenolic Derivatives

Crystallization of trimesic acid (H₃TMA) in the presence of phenol resulted in the single crystals of [(H₃TMA)·(phenol)], 1. The crystal structure consists of two-dimensional hydrogen bonding layers with herringbone geometry via an acid-phenol synthon in which the O−H group of phenol inserts into a conventional acid dimer in an unsymmetrical fashion. The consistency and robustness of this observed phenomenon were confirmed by reproducing a similar structure by treating H₃TMA with m-cresol [(H₃TMA)·(m-cresol)], 2. On the other hand, similar reactions with H₄PMA resulted in unprecedented clathrates of H₄PMA containing a square grid network via a conventional acid synthon. The square grids have dimensions of 8.3 × 8.3 Å and clathrate phenolic guests. Our studies indicate that H₄PMA can act as a host only for the phenolic derivatives such as phenol [(H₄PMA)·(phenol)], 3, o-cresol [(H₄PMA)₂·(o-cresol)], 4, p-cresol [(H₄PMA)₂·(p-cresol)], 5, and p-chlorophenol [(H₄PMA)₂·(p-chlorophenol)], 6.