Crystal Structure Landscape of a Triphenol: Polymorphism and Isostructurality in Solvates and Cocrystals, and Pentameric and Hexameric Aromatic Stacks

Abstract

The crystal structure landscape of 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)-triphenol (TTP) has been examined for its ability to form multicomponent cocrystals. TTP formed kinetic and thermodynamic polymorphic solvate structures and exhibited isosturcturality with different solvates. TTP afforded five different solvates, from four solvents, and a hydrate structure. The solvates are either kinetic or thermodynamic forms; isostructural with different solvents, and polymorphic with a single solvent. Learning from the solvate structures, the crystal engineering of cocrystals from TTP and aza-donors has been examined. The azadonors include 4,4-bipyridine, seven different bipyridines with varying linkers, 4-halopyridines, DABCO, and a di-imidazole. TTP readily formed five different types of cocrystals. The control over the desired cocrystal type can be achieved with control over stoichiometry and choice of solvent. At equimolar stoichiometry, TTP formed isostructural cocrystals in 1:0.5/1:1 ratio (Type-I), by exploiting mutual existence of phenol···phenol and phenol···triazine homosynthons, orthogonal halogen bonding in two cases, and phenol···pyridine heterosynthon, with a large number of diazadonors. Metastable hydrated polymorphs of cocrystals, with high Z′, were also isolated for a few cocrystals. Kinetic cocrystals (Type-II) were obtained with two coformers. THF templates the formation of a large hydrogen bonded ring, mediated by phenol···pyridine heterosynthon, between TTP and two diazadonors, at 1:1.5 stoichiometry (Type-III). At higher stoichiometry of 1:2.5, TTP stabilizes the formation of isostructural cocrystals of pentameric stacks of diazadonors, stabilized through phenol···pyridine and C–H···π heterosynthons (Type-IV). Water-tetramer-assisted hexameric stack was also obtained with an azadonor (Type-V). Overall, TTP resulted in a rich structural landscape of hydrate, solvates, polymorphism in solvates, cocrystals, metastage intermediates, solvates, and stoichiometric polymorphs with azadonors and afforded a general strategy to access a pentameric stack of specific azadonor aromatic molecules.