A Cationic Silver Pyrazine Coordination Polymer with High Capacity Anion Uptake from Water

We
report the first example of linker modification for an N-donor
Ag-based cationic material while maintaining and in some cases increasing
the anion exchange capacity. Cationic silver­(I) pyrazine nitrate selectively
traps harmful oxo-anions from water such as permanganate, perrhenate
and a variety of α,ω-alkanedicarboxylates. We chose these
anions as initial examples of exchange for potential water purification.
The host–guest interaction between the cationic layers of π-stacked
silver pyrazine polymers and the incoming/outgoing interlamellar anions
allows for the exchange. The exchange capacity over 24 h reached 435
and 818 mg/g for permanganate and perrhenate, respectively, a record
for a crystalline metal–organic material and over five times
the exchange capacity compared to commercial resin. The material also
undergoes organic exchange as an analog for pharmaceutical waste,
some of which have a carboxylate functionality at the neutral pH range
typical of natural water sources. Both the as-synthesized and exchanged
materials are characterized by a variety of analytical techniques.