Intermolecular Interactions in the Crystal Chemistry of N,N‘-Diphenylisophthalamide, Pyridine-2,6-dicarboxylic Acid Bisphenylamide, and Related Compounds

The synthesis, characterization, and crystal chemistry of N, N ‘-diphenylisophthalamide ( 1 ) and pyridine-2,6-dicarboxylic acid bisphenylamide ( 2 ) are described. Through a combination of single-crystal X-ray diffraction and molecular orbital and crystal packing calculations, the important intermolecular interactions have been determined. The structures have been compared with the closely related structures, N, N ‘-bis(3-hydroxyphenyl)isophthalamide ( 3 ) and N, N ‘-dimethyl- N, N ‘-diphenylisophthalamide ( 4 ). Crystalline 1 and 2 are isostructural, but there are subtle differences in the conformations and packing as a consequence of intramolecular hydrogen bonding in 2 . This reduces the deviation from planarity in the molecular conformation of 2 and consequently lengthens the intermolecular hydrogen bonding distances. This is reflected in the lattice energies of 1 and 2 (−40.9 and −38.7 kcal/mol, respectively) and in the stacking energies of these compounds. For the compounds that do not contain an N atom in the central ring the progression 3, 1, 4 represents a reduction in the hydrogen-bonding options, reflected in the respective lattice energies: −51.3, −40.9, and −33.3 kcal/mol. The difference between 3 and 1 is in excellent agreement with predictions based on group contributions in structure 3 . In 4 there are no hydrogen bonding options and so C−H···O interactions play a much more important role.