8-Hydroxyquinolinate-Based Metal–Organic Frameworks: Synthesis, Tunable Luminescent Properties, and Highly Sensitive Detection of Small Molecules and Metal Ions

Abstract

Five new metal-organic frameworks, [Zn₂L₂]·2DMF·2MeOH (1), [Zn₂L₂(py)₂] (2), [Cd₂L₂]·Diox·MeOH·6H₂O (3), [Mn₂L₂]·2DMF·2MeOH (4), and [Co₂L₂]·2DMF·4H₂O (5), were assembled by using a novel 8-hydroxyquinolinate derivative H₂L with different metal ions. Complex 1 features a 3D porous network consisting of meso-helical chains ( P + M) built from metal-ligand coordination bonds. The adjacent dinuclear Zn^II building blocks in 2 are connected together to generate a 2D grid network. In complex 3, each binuclear motif is bound to four Zn^II ions to produce a 2D layer structure that stacks into a 3D porous structure. The framework of complex 4 is isostructural to 5, featuring a 2₁ helical chain built from [M₂L₂] units (M = Mn or Co). The adjacent meso-helices associated in parallel are interconnected by the phenolate μ₂-O atoms of H₂L to give rise to a 2D network. Distinct solid-state luminescence properties of 1-3 were observed, arising from their different metal nodes and frameworks. In particular, complex 1 exhibited excellent stability in both common organic solvents and H₂O, thus facilitating its utility as a chemical sensor. Remarkably, luminescent 1 showed highly sensitive detection for nitroaromatic molecules in methanol and Fe³⁺ ion in H₂O even in the presence of other interfering metal cations.