From lamellar net to bilayered-lamella and to porous pillared-bilayer: reversible crystal-to-crystal transformation, CO2 adsorption, and fluorescence detection of Fe3+, Al3+, Cr3+, MnO4−, and Cr2O72− in water

Abstract

An aqua-coordinated lamellar net [Zn(5-NH₂-1,3-bdc)(H₂O)] (1, 5-NH₂-1,3-H₂bdc = 5-amino-1,3-benzenedicarboxylic acid) has been found to undergo a reversible stimuli-responsive 2D-to-2D crystal-to-crystal transformation with a water-free bilayered-lamellar net [Zn(5-NH₂-1,3-bdc)] (1′) upon removal and rebinding of aqua ligands, whereas a 2D porous pillared-bilayer [Zn₂(5-NH₂-1,3-bdc)₂(NI-bpy-44)]·DMF (2, NI-bpy-44 = N-(pyridin-4-yl)-4-(pyridin-4-yl)-1,8-naphthalimide) has been tailored by introducing NI-bpy-44 to replace the coordinated aqua ligands. Pillared-bilayer 2 displayed a moderate CO₂ uptake of 79.1 cm³ g⁻¹ STP at P/P₀ = 1 and 195 K with an isosteric heat of CO₂ adsorption (Q_st) of 37.0 kJ mol⁻¹ at zero-loading. It is noteworthy that the water suspensions of 1 and 2 both displayed good fluorescence performances, which were effectively quenched by Fe³⁺, MnO₄⁻, and Cr₂O₇²⁻ ions and shifted to long wavelengths by Fe³⁺, Al³⁺, and Cr³⁺, even with the coexistence of equal amounts of most other interfering ions. Taking the Stern–Volmer quenching constant, limit of detection, quenching efficiency, anti-interference ability, and visual observation into consideration, it is clear that both 1 and 2 are promising and excellent fluorescent sensors for highly sensitive detection of Fe³⁺, MnO₄⁻, and Cr₂O₇²⁻.