Understanding the Behavior of π-π Interactions in Crystal Structures in Light of Geometry Corrected Statistical Analysis: Similarities and Differences with the Theoretical Models

Statistical analyses on pi-pi interactions among benzenoid dimers and pyridinoid dimers have been performed. The population distributions in these analyses are not in accordance with the theoretical study on benzene dimers and pyridine dimers. A geometrical correction has been proposed and incorporated into the statistical analysis, and then the population distributions have been compared with the theoretical models. The preferred interplanar angles, interplanar distances, offset distances, offset directions, and relative orientation of the pyridyl ring in the T-shaped geometry and relative orientation of the dipoles of two pyridyl rings have been evaluated from the geometry-corrected population distribution. Interestingly, all these parameters are in good agreement with the geometries predicted in a theoretical study. In addition, this analysis also reveals the presence of a small offset in the T-shaped geometry of pyridinoid dimers, which was overlooked in the theoretical study.