Halogen Trimer-Mediated Hexagonal Host Framework of 2,4,6-Tris(4-halophenoxy)-1,3,5-triazine. Supramolecular Isomerism from Hexagonal Channel (X = Cl, Br) to Cage Structure (X = I)

• Published in: Crystal growth & design Vol. 5; no. 3; pp. 887 - 899
• Main Authors: Saha, Binoy K, Jetti, Ram K. R, Reddy, L. Sreenivas, Aitipamula, Srinivasulu, Nangia, Ashwini
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 01.05.2005
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Miscellaneous; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Triazines; Differential scanning calorimetry; Thermogravimetry; Intercalation compounds; Experimental study; Isomerism; Sandwich structures; Clathrates; Intermolecular interaction; Hexagonal lattices; Lamellar structure; Honeycomb structures; Organic compounds; Crystal structure; Synthon
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg049691r

The hexagonal layer structure of host atoms in chloro, bromo, and iodo derivatives of 2,4,6-tris(4-halophenoxy)-1,3,5-triazine, X-POT, is stabilized by a cyclic and cooperative halogen trimer (X···X) synthon. The X···X distance is ∼3.5 Å in isostructural channel inclusion adducts of Cl-POT and Br-POT, whereas I···I is ∼3.8 Å in cage structures of I-POT with aromatic and hydrophobic guests. X-ray crystal structures of I-POT with mesitylene, collidine, tribromomesitylene, triiodomesitylene, hexachlorobenzene, hexafluorobenzene, 1-methylnaphthalene, CH2Cl2, CH2Br2, and CH2I2 guests in R3̄ space group are reported. Host molecules are fully ordered in these isostructural clathrates, whereas guest atoms are disordered except for C6Cl6 and C6F6. The guest molecule resides in a penta-decker sandwich surrounded by double layers of iodo trimer and triazine ring. Supramolecular isomerism from channel to cage framework and the persistent crystallization of trigonal X-POT molecules in high-symmetry host networks (space groups P63/m, P63, R3̄) are discussed in crystal engineering terms:  halogen trimer synthon, C 3 i -Piedfort unit, weak C−H···O/N interactions, changes in size/polarizability of halogen atom, and CSDSymmetry statistics. Br-POT crystallizes in a channel or cage lattice depending on the guest species. Guest release from the cage framework occurs at a higher temperature compared to the channel structure in thermal gravimetric analysis, suggesting applications in organic zeolites. This study illustrates several aspects of crystal engineering from the understanding of intermolecular interactions to the design of crystal structures and their utility as functional solids.