Quantum chemical analysis of noncovalent bonds within crystals. Concepts and concerns

Abstract

While it may seem straightforward to enlist quantum chemical calculations to evaluate the energy of a particular atom-to-atom noncovalent bond within the context of a crystal structure, there are in fact a number of complicating issues that must be understood and dealt with. In addition to the primary bond of interest, the two units will typically be held together as well by secondary interactions, such as H-bonds or π⋯π stacking. Deletion of the groups involved in these secondary bonds perturb the electronic structure of the primary centers. There are also nonspecific interactions that span the breadth of the subunits, such as delocalized electrostatic forces and dispersion. It is important as well to consider how crystal packing forces modify the preferred geometry of not only the two subunits of primary interest but of the entire cluster.