Various carboxylates induced eight Zn(ii)/Cd(ii) coordination polymers with fluorescence sensing activities for Fe(iii), Cr(vi) and oxytetracycline

Abstract

To study the effects of metal ions and various carboxylates on the assembly and structures of coordination polymers (CPs) based on a bis-pyridyl-bis-amide ligand [N,N′-bis(4-methylpyridine-4-yl)-2,6-naphthalene dicarboxylamide] (4-bmnpd), eight Zn(II) and Cd(II) CPs, namely [Cd(4-bmnpd)(2-NBA)₂] (1), [Cd(4-bmnpd)(3-NIP)(H₂O)] (2), [Cd₂(4-bmnpd)(TCPA)₂] (3), [Cd(4-bmnpd)(5-HIP)(H₂O)] (4), [Cd(4-bmnpd)_0.5(5-MIP)(H₂O)] (5), [Cd₃O(4-bmnpd)(1,4-PHDA)₂(H₂O)]·H₂O (6), [Zn(4-bmnpd)(5-MIP)] (7) and [Zn(4-bmnpd)(1,2,4,5-BTA)_0.5]·2H₂O (8) [2-HNBA = 2-nitrobenzoic acid, 3-H₂NIP = 3-nitrophthalic acid, H₂TCPA = tetrachlorophthalic acid, 5-H₂HIP = 5-hydroxyisophthalic acid, 5-H₂MIP = 5-methylisophthalic acid, 1,4-H₂PHDA= 1,4-phenylenediacetic acid and 1,2,4,5-H₄BTA = 1,2,4,5-benzenetetracarboxylic acid] were synthesized under hydrothermal conditions. CPs 1–8 were characterized by elemental analysis, IR and powder X-ray diffraction. Both CPs 1 and 2 are 2D networks. CP 3 shows a 2D 3,4,5-coordinated net based on binuclear nodes. CPs 4 and 5 are 2D lamellar structures with (4,4) and (3,4) topologically connected patterns, respectively. CP 6 is a 3D framework constructed from multi-member [Cd₁₀(1,4-PHDA)₄]_n rhombus rings and 1D [Cd₃O₂]_n chains. CP 7 is a 1D ladder structure. CP 8 is a 2D structure extended by deprotonation of 1,2,4,5-H₄BTA and 4-bmnpd linkers. The influence of the choice of metal as well as the carboxylic acid on the structures of the above CPs is discussed in detail. The fluorescence sensing properties of CPs 1–8 toward metal cations (Fe³⁺), anions (CrO₄²⁻, Cr₂O₇²⁻) and antibiotics (oxytetracycline) were investigated. The limits of detection for Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and oxytetracycline were 6.9 × 10⁻⁵–1.5 × 10⁻⁴, 6.9 × 10⁻⁵–1.3 × 10⁻⁴, 7.7 × 10⁻⁵–1.3 × 10⁻⁴, and 8.5 × 10⁻⁵–9.6 × 10⁻⁴, respectively.