Application of the method for visualization of noncovalent interactions in conformational polymorphs of four organic acids

A method for the visualization of noncovalent interactions using examples of the conformational polymorphs of four organic compounds: 2-(phenyl­amino)­nicotinic, 2-(3-chloro-2-methyl­phenyl­amino)­nicotinic, N-(3-chloro-2-methyl­phenyl)­anthranilic and 2-(methyl­phenyl­amino)­nicotinic acids is examined. The changes in noncovalent contacts are plotted against the angle between the planes of aromatic rings allowing a visual representation of conformational adjustment of molecules as well as packing features of crystal structures. According to the k–Φ criterion, the studied structures represent conformational polymorphs. Different types of hydrogen bonding are discussed within the framework of the method of visualization and molecular Voronoi–Dirichlet polyhedra. Good correlations are found between calculated and experimental data for several cases, such as the agreement between π stacking and polymorphic transition temperatures as well as between the area of a contact and the energy of conjugation. Also, an attempt has been made to assess the relative contributions of conformational and packing polymorphism in the formation of polymorphs.