Crystal-to-Crystal Transformation Caused by Cation Exchange and the Difference in Electrochemical Properties of Three Coordination Polymers

Abstract

In this study, we prepared three highly stable coordination polymers under hydrothermal conditions, {[Zn 2 (μ and {[Pb(μ 4 -DBd)]} n (3). Interestingly, the crystal-to-crystal transformation could occur between 1 and 3 via means of cation exchange. 1 and 2 were two-dimensional structures and 3 was a three-dimensional structure. The structure of 2 contains a continuous hydrogen bond network, which can form an excellent hydrophilic channel. We explored the relationship between cation exchange-induced crystal-to-crystal transformation and water adsorption capacity, and proton conductivity. 1−3 exhibited excellent stability and temperature-and humidity-dependent proton conduction properties. Among these, the water adsorption capacity of 2 was 327.39 cm 3 •g −1 , which was 8.14-fold and 39.23-fold than that of 1 and 3, respectively. The proton conductivity of 2 reached 1.67 × 10 −4 S•cm −1 at 80 °C under 98% relative humidity, which was nearly 2 orders of magnitude higher than the proton conductivity of 1 and 3. All the results indicated that the continuous hydrogen bond network inside the structure was responsible for the transfer of proton and increased the proton conductivity of coordination polymers.

Two Proton Conductive Coordination Polymers Constructed by an Unprecedented Structural Transformation of a Phosphine-Based Tricarboxylate Ligand

“…As the temperature increases from 303 to 353 K, the proton conductivity (σ) value rises from 4.13 × 10 –6 to 3.12 × 10 –5 S cm –1 , indicating that the conductivity of L·2H 2 O has a significant temperature dependence (Table S8). We think the changes in the proton conductivity may be due to the fact that high temperature intensifies the movement of protons and further dissociates enough protons to help increase the value of σ …”

“…45 We think the changes in the proton conductivity may be due to the fact that high temperature intensifies the movement of protons and further dissociates enough protons to help increase the value of σ. 46 Likewise, the conductivity of CPs 1 and 2 also exhibits the obvious humidity dependence. For instance, at a constant temperature (303 K), the σ value of 1 increased by 6 orders of magnitude from 5.41 × 10 −10 (30% RH) to 5.12 × 10 −4 S cm −1 (98% RH) (Figure S9 and Figure 6b).…”