The 50-Fold Enhanced Proton Conductivity Brought by Aqueous-Phase Single-Crystal-to-Single-Crystal Central Metal Exchange.

ABSTRACT

Coordination polymer {[Co3L2(H2O)6]·2H2O}n goes through aqueous-phase single-crystal-to-single-crystal (SC-SC) central metal exchange to produce {[Cu3L2(H2O)6]·2H2O}n. The daughter product presents a higher proton conductivity of 0.004 S cm-1 at 95 °C and 100% RH, increasing by 50-fold relative to the parent product. The water vapor adsorption reveals that the uptake capacity of 2 reaches 145.08 mg/g, which is 7.5 times that of 1 (19.36 mg/g). High water affinity is confirmed by the smaller water contact angle of 2. Replacing water vapor with vapors of dilute hydrochloric acid and ammonia, the improvement of proton conductivity is also realized. Exchanged products all give enhanced conductivities in different vapor atmospheres, which shows that the aqueous-phase central metal exchange is a judicious choice for the preparation of excellent proton conducting coordination polymers.