Aggregation in Three Benzamide or Pyridylcarboxamide Hydrates: Formation of 1D Chains Comprising Water Molecules in a Chloro(pyridyl)benzamide Dihydrate

Three benzamide hydrated derivatives as para-methyl-N-(3-pyridyl)benzamide monohydrate (I) or Mpm H2O; N-(3-fluorophenyl)-4pyridylcarboxamide monohydrate (II) or NpmF H2O and para-chloro-N-(3-pyridyl)benzamide dihydrate (III) or Clpm 2H2O are obtained from a series of crystallization experiments using a range of solvents to obtain polymorphs and solvates (hydrates). Most of the crystallization experiment attempts did not provide hydrates and yielded the starting parent crystalline materials. However, from the experiments, two benzamides, Mpm as a monohydrate and Clpm as a dihydrate were isolated and together with a carboxamide monohydrate as NpmF H2O are reported herein. The water molecules play a key role in crystal structure formation using classical hydrogen bonding via amide N-HOH2, O-HNpyridine and O-HO=C interactions. They compensate for the excess of strong hydrogen bonding acceptors over donors in the benzamide/pyridinecarboxamide molecules, by participating as O-H hydrogen bond donors twice and usually as an O acceptor once. In the Clpm dihydrate, both water molecules form hydrogen bonded chains along the a-axis direction. The lack of hydrate formation in the majority of related benzamides is presumably related to the relative hydrophobicity of these compounds.