A robust and multifunctional calcium coordination polymer as a selective fluorescent sensor for acetone and iron (+3) and as a tunable proton conductor

Abstract

A multifunctional calcium coordination polymer (Ca-CP) formulated as [(CH₃)₂NH₂][Ca(Me₂tcpbH)(H₂O)] (1) has been synthesized and characterized. Compound 1 features a robust and novel three-dimensional (3D) network with cage-like cavities. The high thermal and moisture stability of the title compound makes it a good candidate for possible environment or energy related applications. Fluorescence (FL) studies demonstrate that 1 shows emission with a maximum at 350 nm under 270 nm excitation. The title compound acts as a selective and sensitive fluorescent sensor for the detection of acetone and Fe³⁺ ions at low concentrations. The FL intensity quenching percentage and the concentration ratio of Fe³⁺/Fe²⁺ showed a linear relation with a Fe³⁺ concentration as low as 50 μM in Fe²⁺ aqueous solutions, offering an easy way to probe the extent of Fe²⁺ oxidation. Moreover, due to the relatively high hydration character of Ca²⁺, the terminal water molecules and undeprotonated carboxylate groups form a strong hydrogen-bonded network within the structure, facilitating its tunable proton conduction under various humidity and temperature conditions. The proton conducting mechanism has been investigated using PXRD, IR, and EA methods.