A Water‐Stable Cationic Metal–Organic Framework as a Dual Adsorbent of Oxoanion Pollutants

A three‐dimensional water‐stable cationic metal–organic framework (MOF) pillared by a neutral ligand and with Ni II metal nodes has been synthesized employing a rational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO 4 2− ) ions in the channels, the compound has been employed for aqueous‐phase ion‐exchange applications. The compound exhibits rapid and colorimetric aqueous‐phase capture of environmentally toxic oxoanions (with similar geometries) in a selective manner. This system is the first example of a MOF‐based system which absorbs both dichromate (Cr 2 O 7 2− ) and permanganate (MnO 4 − ) ions, with the latter acting as a model for the radioactive contaminant pertechnetate (TcO 4 − ).