Crystal structure of a 2:1 piroxicam–gentisic acid co-crystal featuring neutral and zwitterionic piroxicam molecules

• Published in: Acta crystallographica. Section E, Crystallographic communications Vol. 72; no. 12; pp. 1714 - 1717
• Main Authors: Horstman, Elizabeth M., Bertke, Jeffery A., Woods, Toby J., Kenis, Paul J. A.
• Format: Journal Article
• Language: English
• Published: United States International Union of Crystallography 01.12.2016
• Subjects: crystal structure; hydrogen bonding; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; piroxicam
• ISSN: 2056-9890; 2056-9890
• DOI: 10.1107/S2056989016017321

A new 2:1 co-crystal of piroxicam and gentisic acid [systematic name: 4-hydroxy-1,1-dioxo- N -(pyridin-2-yl)-2 H -1λ 6 ,2-benzothiazine-3-carboxamide–2-(4-oxido-1,1-dioxo-2 H -1λ 6 ,2-benzothiazine-3-amido)pyridin-1-ium–2,5-dihydroxybenzoic acid, 2C 15 H 13 N 3 O 4 S·C 7 H 6 O 4 ] has been synthesized using a microfluidic platform and initially identified using Raman spectroscopy. In the co-crystal, one piroxicam molecule is in its neutral form and an intramolecular O—H...O hydrogen bond is observed. The other piroxicam molecule is zwitterionic (proton transfer from the OH group to the pyridine N atom) and two intramolecular N—H...O hydrogen bonds occur. The gentisic acid molecule shows whole-molecule disorder over two sets of sites in a 0.809 (2):0.191 (2) ratio. In the crystal, extensive hydrogen bonding between the components forms layers propagating in the ab plane.