Organic Iodide\nCapture in a Titanium Metal–Organic\nFramework Driven by Multiple Noncovalent Interactions

Efficient capture of airborne radioactive alkyl iodines\n(e.g.,\nCH<sub>3</sub>I and CH<sub>3</sub>CH<sub>2</sub>I) released from nuclear\nwaste is vital to environmental protection and human health. The state-of-the-art\nframework sorbents offer the advantage of covalent immobilization\nof alkyl iodines via <i>N</i>-alkylation reaction with large\ncapacity but typically face the essential challenge of sluggish reaction\nrate despite the large existence of open channels for guest diffusion.\nHere, we demonstrate experimentally and theoretically the critical\nrole and superiority of noncovalent interactions in organic iodide\ncapture. Specifically, we document the discovery of a novel topological\ntitanium framework (BIT-61), where the infinite chains of corner-sharing\nTi-centered octahedra with terminal Cl atom and dimethylformamide\nmolecule are connected by aromatic naphthalene-based linkers. Mechanistic\nstudies show that a network of multiple noncovalent binding sites\non pore surface including −CH<sub>3</sub>, Cl, and O atoms\non Ti octahedra as well as electron-rich naphthalene allow for rapid\nconstraint of CH<sub>3</sub>I, CH<sub>3</sub>CH<sub>2</sub>I, and\nCH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>I while maintaining a high\nloading capacity. Particularly, in terms of the average adsorption\nrate (determined at 80% of the maximum uptake capacity), BIT-61 exhibits\na <i>K</i><sub>80%</sub> value of 1.22 g g<sup>–1</sup> h<sup>–1</sup> for CH<sub>3</sub>I, higher than that of reported\nmetal–organic framework and covalent organic framework adsorbents\nwith a maximum time of 61.