Assembly of Effective Halide Receptors from Components. Comparing Hydrogen, Halogen, and Tetrel Bonds

Receptors for halide anions are constructed based on the imidazolium unit and then replacing the H-bonding C–H group first by halogen-bonding C–I and then by tetrel-bonding C–SnH 3 and C–SiF 3 . Attaching a phenyl ring to any of these species has little effect on its ability to bind a halide, but incorporation of a second imidazolium to the benzene connector, forming a bidentate dicationic receptor, greatly enhances the binding. Addition of electron-withdrawing F atoms to each imidazolium adds a further increment. F – consistently binds more strongly to the various receptor models than does Cl – . Whereas replacement of the H atom on the imidazolium groups with the halogen-bonding I has an inconsistent perturbing effect, tetrel-bonding SnH 3 significantly enhances the binding with either halide, and SiF 3 even more so. Placement of the various complexes into aqueous solution reduces binding energies but the trends that occur in the gas phase are largely reproduced in water. The tetrel-bonding receptors are the most selective for F – over Cl – with an equilibrium ratio on the order of 10 14 for SnH 3 and 10 28 for SiF 3 . When combined with their strong halide binding, SiF 3 –ImF 3 –Bz–ImF 3 –SiF 3 +2 bipodal receptors represent an optimal choice in terms of both binding strength and selectivity.