Direct Observation of Confined I − ⋅⋅⋅I 2 ⋅⋅⋅I − Interactions in a Metal–Organic Framework: Iodine Capture and Sensing

Herein a strategy is reported for capturing and sensing iodine by strong I − ⋅⋅⋅I 2 ⋅⋅⋅I − interaction, confined in a metal‐organic framework, [Tb(Cu 4 I 4 )(ina) 3 (DMF)] ( 1 ) (ina=isonicotinate). As revealed by single‐crystal X‐ray crystallography, the uptaken I 2 molecules directly contact the {Cu 4 I 4 } n chains, virtually forming an electronically polarizable tetraiodide anion (I 4 2− ) through strong I − ⋅⋅⋅I 2 ⋅⋅⋅I − interaction. As such, a quasi‐copper‐iodide layer of {Cu 4 I 5 } n with semiconducting characteristics results, leading to a significant enhancement ( Δ σ =10 7 times) in electrical conductivity over the I 2 ‐free 1 . The effect observed is several orders of magnitude higher than those reported due to iodine⋅⋅⋅aromatic interactions ( Δ σ =10 2 times) and by interactions between I 2 and a redox‐active metal centre ( Δ σ =10 4 times). The drastic enhancement in electrical conductivity was used to switch on/off an LED bulb, suggesting the possibility of electrically sensing I 2 .