Distance‐Programmable Sulfonate Pairs as Smart Chelation Pliers for Synergic Alkali/Alkaline‐Earth Ions Harvesting

ABSTRACT A water‐stable metal‐organic framework BUT‐8(Cr)A bearing three classes of distance‐programmable sulfonate pairs (4.3, 5.1, and 7.0 Å) is engineered as “smart chelation pliers” for synergistically harvesting alkali and alkaline‐earth ions. The one‐dimensional channels ( d , 12 Å) are decorated with periodically distributed –SO 3 H micro‐structures that self‐adapt to the bare‐ion diameter range of 1.44–3.34 Å, eliminating pore blockage and accelerating diffusion. In mono‐component solutions, BUT‐8(Cr)A delivers ultrafast equilibrium (∼15 min, C 0 = 10 000 mg L −1 ) and record capacities of 262–550 mg g − 1 for Mg 2+ , Ca 2+ , Na + , K + , Rb + , and Cs + . Real‐time pH tracking reveals that H + ‐M + exchange finishes within 3 min ( C 0 = 100 mg L −1 ), offering a rational and simple indicator for adsorption equilibrium. Regeneration can be achieved through a hot hydrochloric‐acid solution, retaining 91.7% capacity after three cycles. Theoretical and experimental evidences reveal that the pliers II/III (5.1 and 4.3 Å) preferentially capture Mg 2 + , Ca 2 + and Na + , and the pliers I/II (7.0 and 5.1 Å) adopt K + , Rb + and Cs + more easily. This distance‐programmable strategy is distinct from traditional routes focused on constructing flexible adsorption sites. This work unveils the ion‐chelating functionality of sulfonate pairs and elucidates the pivotal role of programmable inter‐site distances in mediating ion self‐adaptation.