Hydrogen-bond patterns in the congruent complex 4-nitrophenol-acetamide (1/1)

Fusion of 4-nitrophenol and acetamide in a 1:1 molar ratio gives the title product, C6H5NO3 center dot C2H5NO, (III), which has the character of a pure covalently bonded compound, having a high sharp melting point. Complex (III) (m.p. 371.9-372.9 K) can be recrystallized from various solvents and forms eutectics with either acetamide or 4-nitrophenol. Similar fusion of mixtures of acetamide and 2-nitrophenol yields no complex similar to (III) and mixtures of acetamide and 3-nitrophenol produce only a weak low-melting complex. The significance of this study lies in its demonstration, via graph set analysis, that some of the patterns found individually in crystalline acetamide or 4-nitrophenol have been preserved in crystals of complex (III), while several higher order graph sets are produced in (III) due to new hydrogen bonds involving the nitro group. In particular, large hydrogen-bonded rings are formed together with helical chains.