Designing functional metal-organic frameworks from a new tripodal carboxylate ligand: Fluorescence sensing and photocatalytic properties

Abstract

A new tripodal carboxylic ligand, 2-(4-carboxylphenoxy) terephthalic acid, readily (H3L) reacts with Cd(II) salts in the presence of N-donor ligands to afford three different metal-organic frameworks of {Cd3(L)2(H2O)4·2CH3CN}n (1), {Cd3(L)2(2,2′-bipy)4·2H2O}n (2), and {Cd3(L)2(phen)2·2CH3CN}n (3). The structure of 1 consists of a 1D metal chain extending to three-dimensional network. The structures of 2 and 3 can be described as a repetition of a trinuclear core with subtle differences. 1–3 exhibit impressive chemical stability, pH stability and strong luminescence, making them excellent candidates as multifunctional fluorescent sensors for selective and sensitive detection of Hg2+, nitroaromatics as well as Cr2O72-. 1–3 are all extremely responsive to Hg2+ ion at a parts per million level, the limits of detection towards Hg2+ ion are 2.55 × 10−6M, 2.72 × 10−6M, and 9.79 × 10−7M for 1–3, respectively. The KSV value for 3 (5.155 × 104M−1) is the highest among most MOFs reported to date. 1–3 represent the first case on the recyclable luminescent probe for Hg2+ ion. Furthermore, the photocatalysis properties of 1–3 for degradation of the Rhodamine B (RhB) have also been examined.