Existence of untypical halogen-involved interactions in crystal packings: A statistical and first-principles study
There is a common perception by the scientific community that a halogen-involved interaction forms when the distance between the donor and the acceptor atoms is less than the sum of their van der Waals (vdW) radii. Our previous work, some theoretical predictions and search in the Cambridge Structural Database (CSD) for crystalline solids with halogen-involved interactions cast doubt on this common perception and lead us to express a challenging question: do halogen-involved interactions exist above the sum of the vdW radii of the contacting atoms? To address this question, we choose 21 couples with similar structures where the main difference between them is the distance between the contacting atoms involved in halogen interactions. To characterize halogen-involved nteractions, we resort to i) periodic and non-periodic density functional theory (DFT) calculations, ii) the quantum theory of atoms in molecules (QTAIM), and iii) the energy decomposition analysis (EDA). In contrast to the common perception, our results indicate that halogen-involved interactions do exist at distances up to 20.74% above the sum of the vdW radii of the contacting atoms which in the same trend with theoretical predictions. Our results modify the current picture of crystal packing which contains halogen-involved interactions, leading to new approaches in designing and engineering of crystals for applications.