Integrating Photoredox and Anion-Binding Capabilities into a Metal–Organic Cage for Iodine Speciation and Sequestration

Abstract

The management of iodine species, notorious for their environmental persistence and health risks, requires innovative materials capable of efficient capture and conversion. Herein, we report the self-assembly and characterization of a Zr-based metal–organic tetrahedron (1) functionalized with redox-active triazatriangulenium (TATA⁺) panels. The cage exhibits a high binding affinity for triiodide (I₃⁻) (ca. 10⁶ M⁻¹) in methanol. The strong host–guest complexation significantly facilitates the disproportionation hydrolysis of I₂ to generate I₃⁻ and HOI. It also enables photocatalytic aerobic oxidation of I⁻ into I₃⁻ within its cavity. Mechanistic investigations revealed the key steps involving guest-to-host photoinduced electron transfer (ET) to generate radicals I^• and 1^• and ET from 1^• to dioxygen to generate superoxide. Solid-state adsorption experiments showed the rapid removal of I₂ and I₃⁻ from water by 1-NTf₂ because of the high affinity for polyiodides. Importantly, although solid-state 1-NTf₂ has no ability to directly adsorb I⁻ from water, we have for the first time developed a light-driven strategy that enables removal of I⁻ through coupled photooxidation and sequestration. This work highlights the significant potential of integrating photoredox-active moieties within stable metal–organic cages for controlling iodine binding and speciation and opens new avenues to address environmental and energy-related sequestration challenges.

Keywords

supramolecular chemistry / metal–organic cage / host–guest chemistry / photoredox activity / iodine speciation and sequestration

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