Solute–solvent halogen bonding during adsorption on silver nanostructures

[Display omitted] ► Silver nanoparticles can induce ionization of 4-iodobenzoic acid in mono- and multi-layer. ► Halogen bonds form between 4-iodobenzoate ions and CCl4 in multilayer. ► DFT and SERS suggest strong interaction between CCl4 and benzoate oxygen atoms. ► Halogen bonding was not observed in the system without silver nanoparticles. We offer here evidence for halogen bonding induced by silver nanoparticles (SNPs) in a multilayer containing 4-iodobenzoate ion (4IBI) and CCl4. SERS experiments show in the monolayer that CCl4 does not adsorb and 4-iodobenzoic acid (4IBA) adsorbs as 4IBI. SEIRA experiments reveal that 4IBI forms in the multilayer during deposition from CCl4 on SNPs. Further infrared experiments on clean BaF2 prove that 4IBI formation caused by underlying SNPs was necessary for CCl4 inclusion in a 4IBI multilayer. Several potential scenarios involving intermolecular attraction between CCl4 and 4IBI are proposed to explain the results. Although halogen bonding involving solvents has been theoretically and experimentally demonstrated in solution phase chemistry, in bulk crystals, and at the monolayer level, here it is shown that halogen bonding interactions can also be significant in multilayer films. Results from this work will likely impact a range of applications across diverse fields where halogen bonding in thin films and nucleation chemistry are important.