Arsenic-Involving Intermolecular Interactions in Crystal Structures: the Dualistic Behavior of As(III) As Electron-Pair Donor and Acceptor

The element arsenic and its compounds pollute fresh water due to their toxicity and are a significant cause of human health problems in some countries. An important way to remove arsenic from freshwater uses intermolecular-interaction-based filters, e.g. based on metal-organic frameworks. Therefore, we need deeper insight and understanding of arsenic-involving intermolecular interactions. In this study, we have selected 77 crystal structures from the Cambridge Structural Database. In each structure, there are one or more As center dot center dot center dot X interactions (X = I, Br, Cl, S, O, As, N, Te). As(III) species can act ambivalently as Lewis acids or bases since they possess a lone pair, unlike As(V) species, which can only act as Lewis acids. However, As filters have so far only been constructed around the assumption that As acts as a Lewis acid. This means that an optimized design of such filters for the dangerous but less considered As(III) species would be important. To facilitate such efforts, here we compare the dualistic intermolecular interaction modes of As(III) compounds to those in As(V) species by using a complementary bonding analysis involving geometrical parameters, the electron localizability indicator, Hirshfeld surfaces, model energies, molecular electrostatic potentials, quantum theory of atoms in molecules, noncovalent interaction index analyses, and natural bond orbitals.