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. 2016;36(6):305-326.
doi: 10.1080/02603594.2016.1171216. Epub 2016 Feb 28.

Experimental and Theoretical Aspects of Anion Complexes with a Thiophene-Based Cryptand

Syed A Haque  1 , Musabbir A Saeed  1 , Afsana Jahan  1 , Jing Wang  1 , Jerzy Leszczynski  1 , Md Alamgir Hossain  1
Affiliations

Experimental and Theoretical Aspects of Anion Complexes with a Thiophene-Based Cryptand

Syed A Haque et al. Comments Mod Chem A Comments Inorg Chem. 2016.

Abstract

Selective recognition of anions has received a tremendous attention in recent years because of their significant importance in biology and environment. This article highlights our recent research on a thiophene-based azacryptand that has been shown to effectively bind anions including iodide, bromide, chloride, nitrate and sulfate. Structural studies indicate that the ligand forms inclusion complexes with chloride and iodide. On the other hand, it forms cleft-like complexes with nitrate and sulfate, where three anions are bound between the cyclic arms. The ligand binds each anion with a 1:1 binding mode in water, exhibiting strong selectivity for sulfate; which is further supported by ESI-MS and DFT calculations.

Keywords: Anion receptor; DFT calculation; association constant; binding energy; host-guest chemistry.

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Figures

Figure 1
Figure 1
Partial 1H NMR spectra (500 MHz) of H6L(Ts)6 in the presence of one equivalent of various anions in D2O at pD = 2.0. [a = ArCH2, b = NCH2CH2, c = NCH2CH2].
Figure 2
Figure 2
1H NMR titrations of H6L(Ts)6 (2 mM) with an increasing amount of NaCl (R = [NaCl]0/[L]0) in D2O at pD = 2.0.
Figure 3
Figure 3
1H NMR spectra of [H6L](Ts)6 (2 mM) with an increasing amount of Na2SO4 (R =[Na2SO4]0/[host]0) in D2O at pD 2.0.
Figure 4
Figure 4
1H NMR titration curves of [H6L](Ts)6 with anions in D2O. The changes in chemical shifts of NCH2CH2 are shown against the increasing ratio of an anion to [H6L]6+.
Figure 5
Figure 5
ESI-MS (positive ion mode) spectrum of the (a) chloride, (b) iodide, (c) nitrate and (d) sulfate complexes. Each solution was prepared from the respective anion salt of L (1.0×10−6 M) in MeOH/H2O (1:1, v/v).
Figure 6
Figure 6
Crystal structure of [H8L(Cl)](Cl)6+ motif in 1 showing one encapsulated and six external chlorides.
Figure 7
Figure 7
Crystal structure of [H6L(Br)(H2O)3]5+ motif in 2 showing one encapsulated bromide and three cleft bound water molecules.
Figure 8
Figure 8
Crystal structure of [H6L(I)(H2O)3]I32+ motif in 3 showing one encapsulated iodide and three cleft bound water molecules.
Figure 9
Figure 9
Crystal structure of [H8L(NO3)3]5+ motif in 4 showing three cleft bound nitrates.
Figure 10
Figure 10
Crystal structure of [H6L(CH3OH)(HSO4)(SO4)2]+ motif in 5 showing the encapsulated methanol and three cleft bound sulfates.
Figure 11
Figure 11
Optimized structure of the encapsulated sulfate in [H6L]6+: perspective view and space filling model calculated at the B3LYP/6-311G(d,p) level of theory. Selected H-bond lengths (Å) of D⋯O [H⋯O]: O1⋯N2, 2.79 [1.649]; O1⋯C2, 3.477 [3.153]; O2⋯N3, 2.907 [1.887]; O2⋯N6, 2.880 [1.835]; O3⋯N5, 2.664 [1.598]; O3⋯N6, 3.195 [2.681]; O4⋯N7, 2.744 [1.690]; O4⋯C3, 2.744[2.379].
Scheme 1
Scheme 1
The ligand L and the electrostatic potential map for [H6L]6+ calculated at the B3LYP/6-311G(d,p) level of theory (red: negative potential, blue: positive potential).
Scheme 2
Scheme 2
The L and the electrostatic potential map for [H6L]6+ calculated at the M06-2X/6-31G(d,p) level of theory (red: negative potential, blue: positive potential).
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