Influence of Coinage Metal(111) Surfaces on the Halogen Bond Strength of Bromo/Iodobenzene
The concept of halogen bonding strength is well established, with its strength increasing with the polarisability of the halogen, resulting in the following order within the gas phase: F < Cl < Br < I. However, a recent experimental study has shown that the known order can change when the halogen bond occurs on a surface. Overall, a halogen bond is formed by the interaction between a high electron density region of one molecule and a low electron density region (the σ hole) of a second molecule. When the σ hole is no longer planar with the high electron density region of the other molecule, the strength of the halogen bond is weakened. The influence of the σ hole orientation on the halogen bonding strength was investigated in this study using bromo/iodobenzene on metal(111) surfaces (Cu, Ag and Au). Quantum chemical calculations showed that the Br σ hole orientation is not affected by the coinage metal surface. However, the I σ hole is otherwise oriented towards the Cu(111) surface, weakening the halogen bond. A similar phenomenon occurs on a Ag(111) surface but not on Au(111). This is described in: DOI: 10.1021/acs.jpcc.3c07555.
