Polymorphs, hydrates and solvates of a co-crystal of caffeine with anthranilic acid.
A polymorph screen on a new 1:1 co-crystal of caffeine, C8H10N4O2, with anthranilic acid, C7H7NO2, has revealed a rich diversity of crystal forms (two polymorphs, two hydrates and seven solvates, including two sets of isostructural solvates). These forms were prepared by liquid-assisted grinding and solution crystallization, and the crystal structures of nine of these forms have been solved using either single-crystal or powder X-ray data. The structures contain O-H...N and N-H...O hydrogen bonds through which caffeine and anthranilic acid molecules assemble to form zigzag-type chains. These chains can interact in an anti-parallel and offset manner to form cage- or channel-type skeletons within which solvent molecules can be located, giving rise to the diversity of forms observed for this co-crystal. In contrast, an equivalent series of liquid-assisted grinding and solution crystallization experiments with the closely related system of theobromine, C7H8N4O2, and anthranilic acid resulted in the formation of only one 1:1 co-crystal form.
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England.
Nadeesh
N
Madusanka
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England.
Mark D
MD
Eddleston
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England.
Mihails
M
Arhangelskis
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, England.
William
W
Jones
D001969:Bromobenzenes / Q000737:chemistry; D002110:Caffeine / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D000697:Central Nervous System Stimulants; D002722:Chlorobenzenes / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D033362:Powder Diffraction; D012997:Solvents / Q000737:chemistry; D013818:Thermogravimetry; D014050:Toluene / Q000737:chemistry; D014992:Xylenes / Q000737:chemistry; D062367:ortho-Aminobenzoates / Q000737:chemistry*
D001969:Bromobenzenes; D000697:Central Nervous System Stimulants; D002722:Chlorobenzenes; D012997:Solvents; D014992:Xylenes; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; D014050:Toluene; D002110:Caffeine; C032036:bromobenzene; C031294:chlorobenzene
co-crystals; hydrates; polymorphism; solvates