Ferrocenyl-triazole complexes and their use in heavy metal cation sensing

Abstract

Complexes tris((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (3), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (6), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)ether (7), and 1-ferrocenyl-1H-1,2,3-triazol-4-yl)methanamine (9) were synthesized using the copper-catalyzed click reaction. Complexes 3, 6, 7, and 9 were characterized using NMR (¹H and ¹³{¹H}) and IR spectroscopy, elemental analysis, and mass spectrometry. Structures of 3, 7, and 9 in the solid state were determined using single-crystal X-ray diffraction. It was found that the triazole rings were planar and slightly twisted with respect to the cyclopentadienyl groups attached to them. Chains and 3D network structures were observed due to the presence of π⋯π and C-H⋯N interactions between the cyclopentadienyl and triazole ligands. A reversible redox behavior of the Fc groups between 239 and 257 mV with multicycle stability was characteristic for all the compounds, revealing that the electrochemically generated species Fc⁺ remained soluble in dichloromethane. Electrochemical sensor tests demonstrated the applicability of all the complexes to enhance the quantification sensing behavior of the screen-printed carbon electrode (SPCE) toward Cd²⁺, Pb²⁺, and Cu²⁺ ions.

Scheme 1. Reaction of 1 with 2, 4, 5, or 8 forming the ferrocenyl triazoles 3, 6, 7, and 9; (i) 1st step: solution A: thf–H₂O (ratio 7 : 1, v/v), for 3: (3.3 equiv. of 1, 1.0 equiv. of 2), for 6 or 7: (2.2 equiv. of 1, 0.15 equiv. of 3, 1.0 equiv. of 4 or 5, respectively), for 9: (1.1 equiv. of 1, 0.15 equiv. of 3, 1.0 equiv. of 8); 2nd: 0.3 equiv. of CuSO₄ in H₂O; 3rd: 3.0 equiv. of Na–ascorbate in H₂O; 4th: 25 °C, 48 h.; 5th: washing with NH₃ (until colorless), then with H₂O (pH = 7.00).

Fig. 1. ORTEP (50% probability level) of the molecular structure of 3 with the atom numbering scheme. Hydrogen atoms are omitted for clarity. Symmetry operation for generating equivalent atoms: ‘A’ = −y + 1, x − y, z. ‘B’ = −x + y + 1, −x + 1, z.

Fig. 2. ORTEP (50% probability level) of the molecular structure of 7 with the atom numbering scheme. Hydrogen atoms are omitted for clarity.

Fig. 3. ORTEP (50% probability level) of the molecular structure of 9 with the atom numbering scheme. Hydrogen atoms are omitted for clarity. The two crystallographically different molecules of 9 are denoted as A (including Fe1) and B (including Fe2).

Fig. 4. (A) Hirshfeld surfaces of 3 mapped over d_norm, (B) Hirshfeld surfaces of 7 mapped over d_norm, (C) Hirshfeld surfaces of 9 mapped over d_norm.

Fig. 5. Cyclic voltammograms of 1.0 mM solution of 3 (red line), 6 (violet line), 7 (black line), and 9 (blue line), scan rate 100 mV s⁻¹ in anhydrous dichloromethane with [NⁿBu₄][PF₆] (0.1 mol L⁻¹) used as a supporting electrolyte at 25 °C.

Fig. 6. Cyclic voltammograms of 5.0 mM [Fe(CN)₆]^3−/4− using: (A) bare SPCE (solid line), 3@SPCE (dashed dotted line); (B) bare SPCE (solid line), 6@SPCE (dashed dotted line); (C) bare SPCE (solid line), 7@SPCE (dashed dotted line); (D) bare SPCE (solid line), 9@SPCE (dashed dotted line); scan rate 100 mV s⁻¹ in aqueous solution containing 0.1 M KCl used as a supporting electrolyte at 25 °C.

Fig. 7. Square wave voltammograms of ABS solutions of Cd²⁺, Pb²⁺, and Cu²⁺ (250 μM) using a drop-casting method for the bare SPCE and 3@SPCE modified electrodes.

Fig. 8. Square wave voltammograms for simultaneous detection of SAB solutions of Cd²⁺, Pb²⁺, and Cu²⁺ metal ions (150.0 μM) using a drop-casting method for bare SPCE and the modified electrodes 3@SPCE, 6@SPCE, 7@SPCE, and 9@SPCE.

Fig. 9. Square wave voltammograms (insets: linear calibration plots) for the simultaneous detection of SAB solutions of Cd²⁺, Pb²⁺, and Cu²⁺ metal ions (0.0–1000.0 μM) using a drop-casting method for the modified electrodes: (A) for 3@SPCE; (B) for 6@SPCE; (C) for 7@SPCE; (D) for 9@SPCE.