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