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. 2015 Jan 1;5(48):38733-38741.
doi: 10.1039/C5RA02372F. Epub 2015 Apr 21.

Colorimetric and Optical Discrimination of Halides by a Simple Chemosensor

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Free PMC article

Colorimetric and Optical Discrimination of Halides by a Simple Chemosensor

Syed A Haque et al. RSC Adv. .
Free PMC article

Abstract

A thiophene-based tripodal copper(II) complex has been synthesized as a new colorimetric and optical chemosensor for naked-eye discrimination of halides in acetonitrile and an acetonitrile-water mixture. The binding interactions of the new receptor with several anions were analyzed by UV-Vis titrations, electrospray ionization mass spectrometric (ESI-MS) experiments and density functional theory (DFT) calculations. The results from UV-Vis titrations indicate that the coordinative unsaturated copper(II) complex strongly binds a halide at its vacant copper(II) centre via a metal-ligand bond forming a 1:1 complex, exhibiting binding affinities in the order of fluoride > chloride > bromide > iodide. The interactions of the receptor with halides were further confirmed by ESI-MS, showing a distinct signal corresponding to a 1:1 complex for each halide, suggesting that the noncovalent interactions also exist in the gas phase. In addition, time-dependent DFT (TD-DFT) calculations were also carried out to understand the excited-state properties of the chemosensor complexes. A detailed analysis of the TD-DFT calculations shows a consistent red-shift in the first optically-allowed transition, consistent with the observed colorimetric experiments.

Figures

Fig. 1
Fig. 1
ESI-MS spectrum of 1 in CH3CN.
Fig. 2
Fig. 2
Colorimetric studies of anions (F, Cl, Br, I, NO3 and ClO4) with 1 in CH3CN at room temperature.
Fig. 3
Fig. 3
Colorimetric studies of anions (F, Cl, Br, I, NO3 and ClO4) with 1 in CH3CN-H2O (4:1, v/v) at room temperature.
Fig. 4
Fig. 4
Changes in absorbance of 1 (1 x 10−4 M) in the presence of one equivalent of different halides in CH3CN at room temperature. λmax: 1 = 291, I = 290, Br = 310, Cl = 289, F = 270 nm.
Fig. 5
Fig. 5
Changes in absorption spectra of 1 (1 x 10−4 M) with an increasing amount of fluoride (a), bromide (b), chloride (c) and iodide (d) in CH3CN. The titration curves are shown in insets.
Fig. 6
Fig. 6
Job plot analysis of 1 for the binding of fluoride in CH3CN. The change of the absorbance (ΔI) of 1 was determined from the titration plot as shown in Figure 5a.
Fig. 7
Fig. 7
ESI-MS spectra of 1 in the presence of one equivalent of (a) fluoride, (b) chloride, (c) bromide and (d) iodide in CH3CN.
Fig. 8
Fig. 8
(a) Optimized structures (1st column) of halide complexes of 1 calculated with density functional theory (DFT) using the M06L meta-GGA functional [Colour codes: gray = carbon, pink = nitrogen, orange = copper. Hydrogen atoms are not shown for clarity]; (b) Occupied (2nd column) and virtual orbitals (3rd column) contributing to the first excited-state transition for the various complexes obtained from TD-DFT calculations.
Scheme 1
Scheme 1
(a) Free amine L, copper complex [CuII(L)]2+ (1), and proposed halide-bound complex [1(X)], (b) Optimized structure of 1 calculated with density functional theory (DFT) performed using the M06L meta-GGA functional.

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