Modulator-Directed\nCounterintuitive Catenation Control\nfor Crafting Highly Porous and Robust Metal–Organic Frameworks\nwith Record High SO<sub>2</sub> Uptake Capacity

Sulfur\ndioxide (SO<sub>2</sub>) is an important industrial feedstock\nthat can be directly utilized or catalytically transformed to value-added\nchemicals such as sulfuric acid. The development of regenerable porous\nsorbents for the highly efficient storage and energy-minimal release\nof toxic SO<sub>2</sub> operating under ambient conditions has attracted\ngrowing interest. Herein, we report the topology-guided construction\nof highly porous <b>acs</b>-type metal–organic frameworks\n(MOFs) through a counterintuitive modulator-directed catenation control\napproach. In contrast to the conventional modulator facilitated coordination\ncompetition that favors the thermodynamic catenated phase, we show\nthat the elevation of modulator concentration can promote the formation\nof the noncatenated phase probably through a sublattice dissolution\npathway. The assembly of a custom-designed trigonal prismatic triptycene-quinoxaline\nlinker and trinuclear Fe<sub>3</sub>O cluster affords either the threefold\ncatenated SJTU-219 or noncatenated SJTU-220 with desired <b>acs</b> net. Impressively, the synthetic approach is applicable to various\nmetal ions, including Al<sup>3+</sup>, V<sup>3+</sup>, and even Ti<sup>4+</sup>. The noncatenated SJTU-220 exhibits an extraordinary SO<sub>2</sub> sorption capacity of 29.6 mmol g<sup>–1</sup> at 298\nK and 1 bar, surpassing all reported solid sorbents. The uptake capacity\ncan be further raised to 35.6 mmol g<sup>–1</sup> via the replacement\nof Fe<sup>3+</sup> with kinetically more inert Cr<sup>3+</sup>, resulting\nin a staggering ∼329-fold volume reduction compared with free\nideal SO<sub>2</sub> gas. Computational simulations suggest that unique\nFe<sup>3+</sup>···S(SO<sub>2</sub>) interactions dominate\nthe SO<sub>2</sub> seeding process, facilitating the efficient packing\nof SO<sub>2</sub> molecules in the large channels. Besides, the exceptionally\nlow uptake at the low pressure region implies global weak framework-SO<sub>2</sub> interactions, which offer great potential for practically\nimplementing an “easy-on/easy-off” SO<sub>2</sub> delivery\nsystem.