Stacking interactions between two benzene molecules that coordinate transition metal ions within organometallic sandwich and half-sandwich compounds were investigated by performing Cambridge Structural Database (CSD) search and DFT-D calculations. Calculations of interaction energies revealed that stacking interactions between coordinating benzenes of sandwich (-3.69 kcal/mol) and half-sandwich compounds (-3.29 kcal/mol) are significantly stronger than the stacking interaction between noncoordinating benzenes (-2.7 kcal/mol). At large horizontal displacements (offset r = 5.0 angstrom), these sandwich parallel to sandwich interactions are remarkably strong (-3.03 kcal/mol)) while half-sandwich parallel to half-sandwich interactions are significantly weaker (-1.27 kcal/mol). The results of calculations are in good agreement with the data in the crystal structures from the CSD, where 76 of sandwich parallel to sandwich contacts have large horizontal displacements, which is significantly more than 46 of half-sandwich parallel to half-sandwich contacts arranged in this fashion. The study provides valuable information about interactions of aromatic molecules relevant to crystal engineering, materials design, and molecular recognition.
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