Mechanism-Property Correlation in Coordination Polymer Crystals toward Design of a Superior Sorbent.

A methodology was developed to design superior sorbents of oxoanions. To integrate the high efficiency of chemisorption, selectivity, and recyclability into one sorbent, understanding the nature of oxoanions-sorbent interactions and the structural evolution of the sorbents is essential. Three cationic Ag(I) coordination polymers (CPs) are synthesized for dichromate (Cr2O72-) removal, and three distinct oxoanion-exchange mechanisms are identified, namely, the replacement, breath, and reconstruction processes, depending on the degree of framework distortion induced by the dichromate-CP interactions. The single crystal to single crystal transformation during the oxoanion exchange has been investigated by using single-crystal X-ray diffraction and energy-dispersive X-ray microanalysis. The replacement process, due to a weak chemisorption, shows excellent recyclability at the cost of reduction of efficiency and selectivity of adsorption. The reconstruction process may achieve a high efficiency and selectivity, but it loses recyclability. Due to the formation of a Ag-O(dichromate) bond and the breathing effect of the framework, the sorbent with the breath mechanism shows both superior efficiency and high recyclability in dichromate removal. The study of perrhenate (ReO4-) removal using the same CPs demonstrates that one CP performing the reconstruction process during dichromate removal turns to the breath process in removal of perrhenate anions. These results of mechanism-property correlation provide an insight into improvement of the methodology to fabricate a superior CP sorbent for oxoanion removal.