Metal-ion binding by cyclic halogen-bonded structures: A theoretical study using M-(BrZ)₄ clusters (Z = F or NH₂; M = Li⁺, Na⁺, or Mg²⁺)

The ability of a cyclic halogen-bonded network to bind a metal ion is explored using M-(BrZ)4 complexes (M = Li+, Na+, or Mg2+; Z = F or NH2). Binding is characterized by bond paths connecting the metal ion with each one of the bromine atoms in the host, and orthogonal to the Br⋯Z interactions. Binding energies are substantial and follow the order Na+ < Li+ 蠐 Mg2+. The electron densities at the Br⋯M bond critical points are generally smaller than their Br⋯Z counterparts for the monovalent ions, but significantly larger for Mg2+. Both Br⋯M and Br⋯Z interactions are found to be non-covalent in nature.