The Role of π-Stacking in the Composition of Phloroglucinol and Phenazine Cocrystals

• Published in: Crystal growth & design Vol. 8; no. 12; pp. 4546 - 4552
• Main Authors: Sarma, Bipul, Reddy, L. Sreenivas, Nangia, Ashwini
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Washington,DC American Chemical Society 03.12.2008
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Solid-solid transitions; Specific phase transitions; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Crystal growth; Stoichiometry; Stacking sequence; Crystallization; Template reaction; Cocrystallization; Sandwich structures; Monocrystals; Phenol; Pyridine; Hydrogen bonds; Cocrystal; Phenols; Dimers; Hydrates; Polymorphism; Crystal structure; Synthon
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg800585d

Cocrystallization of phloroglucinol (PHG) and phenazine (Phen) afforded cocrystals of 1:1.5, 1:1.75, and 1:2 PHG·Phen stoichiometry upon grinding the two components in different starting ratios and then using suitable solvents for single crystal growth. The phenol···pyridine O−H···N synthon directs 1:1.5 bimolecular organization of PHG and Phen molecules in a π-stacked motif (cocrystal 1). Additional phenazine molecules insert in the π-stacks to give a higher proportion of the aromatic species in cocrystals 2 and 3 (1:1.75 and 1:2). A hydrate cocrystal of 1:2:1 composition (4) was also obtained. The π-stack dimer motif of phenazine templated by the 1,3-(OH)2 moiety of phloroglucinol at about van der Waals distance in these crystal structures is postulated to promote the crystallization of the β-phenazine polymorph having a sandwich herringbone motif. These results suggest a role for cocrystal formers as hydrogen bond additives that favor and stabilize specific motifs for the crystallization of new polymorphs.