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

A new 2:1 co-crystal of piroxicam and gentisic acid [systematic name: 4-hy­droxy-1,1-dioxo-N-(pyridin-2-yl)-2H-1λ(6),2-benzo­thia­zine-3-carboxamide–2-(4-oxido-1,1-dioxo-2H-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.