Crystal Packing and Hydrogen-Bonding Studies: The Crystal and Molecular Structures of the Nonhydrate and Hydrate Forms of 2,6-Di(propanoylamino)pyridine

The crystallization of 2,6-di(propanoylamino)pyridine ([CH3(CH2)n-1CONH]2C5H3N, n = 2, [2Apy]) from hexane/ethyl acetate mixed solvent gives two types of crystals, 2APy and 2Apy · 2H2O. The crystal data, packing structures, and hydrogen bonding network of both crystals suggest that 2APy and 2APy · 2H2O are not structurally similar. In the crystal structure analysis of 2APy, two crystallographically independent 2APy molecules were observed in its asymmetric unit, whereas the asymmetric unit of 2APy · 2H2O consists of one crystallographically independent 2APy molecule and two crystallographically independent water molecules (Ow, Ow′). The water molecules (Ow, Ow′) are connected via Ow…Ow′ intermolecular hydrogen bonds to form two chains in a one-dimensional arrangement along the direction of c-axis, built up of two crystallographically independent water molecules. The driving force behind the molecular aggregation of 2APy is mainly N…O = C hydrogen bonding, whereas those of 2APy · 2H2O are N…Ow, C = O…Ow, and Ow…Ow′ hydrogen bonding. The differences in the kind of hydrogen bonding networks in both crystals contribute to the differences in the packing modes observed in 2APy and 2APy · 2H2O.