Anion-dependent dynamic structure and tunable luminescence of Zn-MOFs with carboxyphenyl-terpyridine ligands

Abstract

Based on a cationic layered Zn-MOF (1⊃NO₃⁻) with free NO₃⁻ anions located in the interlayer channels, two anion-exchanged compounds (1⊃ClO₄⁻ and 1⊃BF₄⁻) were achieved by replacing free NO₃⁻ anions with ClO₄⁻ or BF₄⁻ anions. However, an anion-induced structural transformation occurred during the Cl⁻ anion exchange with coordinated NO₃⁻ anions replaced by Cl⁻anions, resulting in the formation of a 2D hcb layered structure (2) and a 3D ths framework (3). The transformation process is fully investigated by means of FT-IR, PXRD and SC-XRD, revealing anion-dependent structural dynamism of the framework. More interestingly, these MOFs demonstrated anion-dependent tunable luminescence evidenced by different fluorescence intensities in the solid state as well as highly sensitive but varied detection capabilities for nitroaromatics. Thus, the MOFs presented here can be used as an ideal platform to deeply explore the possible transformation mechanism, and various tunable luminescent behavior related to the nature of anions, including sizes/shapes, geometries, their coordinating tendencies to metal, and their different hydrogen-bonding abilities with the framework.