Dimeric iodine(i) and silver(i) cages from tripodal N-donor ligands via the [N–Ag–N]+ to [N–I–N]+ cation exchange reaction

Abstract

The directionality of the [N–I–N]+ halogen bond makes iodine(I) ions impeccable tools in the design and construction of [N–I–N]+ halogen-bonded assemblies. The synthesis of dimeric iodine(I) cages with imidazole-derived N-donor tripodal ligands is described, as well as their corresponding silver(I) precursors. The addition of elemental iodine to the parent two-coordinate Ag(I) complexes produces iodine(I) complexes with three-center four-electron (3c–4e) [N–I–N]+ bonds. Complex formation via this cation exchange was confirmed by 1H and 1H–15N HMBC NMR studies in solution, and additionally by electrospray ionisation and ion mobility mass spectrometry analysis (MS) in the gas phase. The structural analysis of the single crystal X-ray structures of 11 silver(I) cages and the computationally modelled iodine(I) cages, along with MS analysis, revealed structural similarities between the two different capsular assemblies. In addition to strong electrostatic interactions, C–H⋯F hydrogen bonds were determined to have a directing effect on the silver(I) cage formation and binding of suitably sized anions into the cavities in the solid state.