Exceptional Perrhenate/Pertechnetate Uptake and Subsequent Immobilization by a Low-Dimensional Cationic Coordination Polymer: Overcoming the Hofmeister Bias Selectivity

Abstract

We report one of the most efficient scavenger materials, a cationic crystalline coordination polymer SBN for trapping ReO 4 –, a surrogate for 99 TcO 4 –, as an anionic radioactive contaminant of great concern. The uptake capacity for ReO 4 – reaches 786 mg/g, a value noticeably higher than the state of art anion-exchange resins and other inorganic or hybrid anion sorbents. Once being captured, ReO 4 – is greatly immobilized, as almost no ReO 4 – can be eluted using large excess of nitrate, carbonate, and phosphate anions. The processes are featured by a complete and irreversible single-crystal to single-crystal structural transformation from SBN to the ReO 4 – -incorporated phase (SBR). The coordination environments of NO 3 – and ReO 4 – probed by single-crystal structures clearly unravel the underlying mechanism, where each ReO 4 – in SBR binds to multiple Ag + sites forming strong Ag–O–Re bonds, and to 4,4′-bipyridine through a dense hydrogen bond network. These structural insights lead to a significant difference in solubility product constants between SBN and SBR, which is further confirmed by first principle calculations showing a large binding energy difference of 35.61 kcal/mol. To the best of our knowledge, SBR is the least soluble perrhenate/pertechnetate salt reported, which may be considered as a potential waste form for direct immobilization of TcO 4 – .