The crystal structure of the zwitterionic co-crystal of 2,4-dichloro-6-{[(3-hydroxypropyl)azaniumyl]methyl}phenolate and 2,4-dichlorophenol

The title compound, C10H13Cl2NO2·C6H4Cl2O, was formed from the incomplete Mannich condensation reaction of 3-aminopropan-1-ol, formaldehyde and 2,4-dichlorophenol in methanol. This resulted in the formation of a co-crystal of the zwitterionic Mannich base, 2,4-dichloro-6-{[(3-hydroxypropyl)azaniumyl]methyl}phenolate and the unreacted 2,4-dichlorophenol. The compound crystallizes in the monoclinic crystal system (in space group Cc) and the asymmetric unit contains a molecule each of the 2,4-dichlorophenol and 2,4-dichloro-6-{[(3-hydroxypropyl)azaniumyl]methyl}phenolate. Examination of the crystal structure shows that the two components are clearly linked together by hydrogen bonds. The packing patterns are most interesting along the b and the c axes, where the co-crystal in the unit cell packs in a manner that shows alternating aromatic dichlorophenol fragments and polar hydrogen-bonded channels. The 2,4-dichlorophenol rings stack on top of one another, and these are held together by π-π interactions. The crystal studied was refined as an inversion twin.