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Four H-binding HCl and HF molecules position themselves at the vertices of a tetrahedron when surrounding a central Cl-. Halogen bonding BrF and ClF form a slightly distorted tetrahedron, a tendency that is amplified for ClCN which forms a trigonal pyramid. Chalcogen bonding SF2, SeF2, SeFMe, and SeCSe occupy one hemisphere of the central ion, leaving the other hemisphere empty. This pattern is repeated for pnicogen bonding PF3, SeF3 and AsCF. The clustering of solvent molecules on one side of the Cl- is attributed to weak attractive interactions between them, including chalcogen, pnicogen, halogen, and hydrogen bonds. Binding energies of four solvent molecules around a central Na+ are considerably reduced relative to chloride, and the geometries are different, with no empty hemisphere. The driving force maximizes the number of electronegative (F or O) atoms close to the Na+, and the presence of noncovalent bonds between solvent molecules.
Scheiner, S. I., Michalczyk, M., Zierkiewicz, W. (2019). Structures of clusters surrounding ions stabilized by hydrogen, halogen, chalcogen, and pnicogen bonds. Chemical Physics, 524, 55 - 62. http://www.sciencedirect.com/science/article/pii/S0301010419301600
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