Parallel interactions at large horizontal displacement in pyridine-pyridine and benzene-pyridine dimers.

A study of crystal structures from the Cambridge Structural Database (CSD) and DFT calculations reveals that parallel pyridinepyridine and benzenepyridine interactions at large horizontal displacements (offsets) can be important, similar to parallel benzenebenzene interactions. In the crystal structures from the CSD preferred parallel pyridinepyridine interactions were observed at a large horizontal displacement (4.06.0 angstrom) and not at an offset of 1.5 angstrom with the lowest calculated energy. The calculated interaction energies for pyridinepyridine and benzenepyridine dimers at a large offset (4.5 angstrom) are about 2.2 and 2.1 kcal?mol-1, respectively. Substantial attraction at large offset values is a consequence of the balance between repulsion and dispersion. That is, dispersion at large offsets is reduced, however, repulsion is also reduced at large offsets, resulting in attractive interactions.