Coordinated water modulation for proton conductivity via post-synthetic transmetalation in yttrium-based coordination polymers

Abstract

Understanding the correlation between structural variations and proton transport in coordination polymers (CPs) is essential for developing efficient solid-state proton conductors (SSPCs). In this study, we demonstrate that post-synthetic transmetalation via alkali metal exchange enhances proton conductivity in a pseudo-three-dimensional yttrium-based CP, {[Y(H₂O)₄(HDSNDC)]·H₂O}_n (H₄DSNDC = 4,8-disulfonaphthalene-2,6-dicarboxylic acid). Immersion in 1 M KCl solution induces transmetalation, yielding a potassium-substituted analogue, {K₃(H₂O)₂(HDSNDC)}_n. Structural analysis reveals that transmetalation induces structural reorganization, in which terminal H₂O ligands are converted into μ-bridging ones. These bridging H₂O ligands exhibit increased acidity due to cooperative polarization by adjacent K⁺ ions, facilitating proton dissociation and significantly enhancing conductivity from 7.23 × 10⁻⁵ S cm⁻¹ for Y-DSNDC to 2.50 × 10⁻³ S cm⁻¹ for K-DSNDC at 363 K under 95% RH. This work highlights transmetalation-induced coordination tuning as an effective strategy to enhance proton transport in CPs.