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.