Rational synthesis of a luminescent uncommon (3,4,6)-c connected Zn(ii) MOF: a dual channel sensor for the detection of nitroaromatics and ferric ions

Abstract

The articulate combination of intriguing functional groups and luminescence properties can deliver metal–organic frameworks (MOFs) with multifarious applications viz. selective and specific sensing of nitroaromatic compounds (NACs), an important constituent of explosives, as well as sensing of toxic metal ions. In this regard, a new d¹⁰ configuration based Zn(II) metal–organic framework (MOF) {(NH₂(CH₃)₂)[Zn₄(ddn)₂(COO)(H₂O)₄]·solvent}_n (1) has been synthesized using a π-conjugated and rigid multicarboxylate ligand 3,5-di(3,5-dicarboxylphenyl)nitrobenzene (H₄ddn). 1 displays a 3D (3,4,6)-c connected net which is based on two types of binuclear [Zn₂(μ₂-COO)₂(μ₁-COO)₂] and [Zn₂(μ₂-COO)₄] clusters. Sensing studies of 1 to detect nitro-aromatic compounds reveal highly specific detection of 2,4-dinitophenol (DNP) with remarkable quenching (K_SV = 8.93 × 10³ M⁻¹) and a low limit of detection (LOD: 1.12 ppm). The luminescence quenching mechanism in the case of 1 in the presence of NACs has been ascribed to the concurrent presence of the charge transfer as well as the weak interaction between the MOF and NACs. The activated framework of 1 also displayed highly selective detection of ferric ions with K_SV = 1.13 × 10⁴ M⁻¹ with a low limit of detection (LOD: 1.24 ppm).