Anion recognition in aqueous solution by cyclic dinuclear square cage-shaped coordination complexes

Article abstract of DOI:10.1016/j.ica.2019.118961

Three cyclic dinuclear complexes, namely [M₂(H₂L)₂](ClO₄)₄ [M = Co²⁺ (1), Ni²⁺ (2), Zn²⁺ (3), H₂L = (1,2)-bis-N'-(pyridin-2-ylmethylene)benzohydrazide hydrazine, C₂₆H₂₂N₈O₂], containing amide and hydrazine groups were synthesized and characterized. Each central metal ion is coordinated with two oxygen atoms and four nitrogen atoms from carbonyl, and pyridine and imine, respectively. The metal ion is six-coordinated and has a slightly deformed octahedral geometry. X-ray crystallographic analyses showed that all the three cyclic dinuclear complexes crystallize in the orthorhombic system, and belong to the C222 space group, with two molecules in each unit cell. The cyclic dinuclear molecule is linked by two H₂L ligands with a Z-form-HN-NH-bridge, nearly forming a square coordination cage with edges of length around 8.4 ?. The cyclic dinuclear complexes can recognize acetate and fluoride anions in an acetonitrile solution containing 60% volume water. Recognition is governed by electrostatic interactions in cooperation with the cage structure effect with the mechanism of anion displacement reaction. The results show that the recognition of anions in acetonitrile aqueous solution is an exothermic and entropy-reducing reaction. This suggests that the enthalpy change plays an important role in the presence of highly polar water and highlights the importance of positively charged cage structure effect. A color change from light yellow to dark yellow was clearly observed for complex 3 on addition of acetate or fluoride anions in acetonitrile aqueous solution containing 60% water. Complex 3 can be used for colorimetric “naked eye” recognition of acetate or fluoride anions in acetonitrile aqueous solution. Theoretical calculations based on time dependent density functional theory (TD-DFT) show the agreement between the theoretical results and experimental data.

Full text of DOI:10.1016/j.ica.2019.118961

Accepted Manuscript
Research paper
Anion Recognition in Aqueous Solution by Cyclic Dinuclear Square Cage-sha-
ped Coordination Complexes
Cai-Ye Fu, Yu-Qian Li, Lu Chen, Yun-Guang Wang, Li-Rong Lin
PII:
S0020-1693(19)30689-9
https://doi.org/10.1016/j.ica.2019.118961
118961
DOI:
Article Number:
Reference:
ICA 118961
Inorganica Chimica Acta
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Received Date:
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Accepted Date:
15 May 2019
11 June 2019
11 June 2019
Please cite this article as: C-Y. Fu, Y-Q. Li, L. Chen, Y-G. Wang, L-R. Lin, Anion Recognition in Aqueous Solution
by Cyclic Dinuclear Square Cage-shaped Coordination Complexes, Inorganica Chimica Acta (2019), doi: https://
doi.org/10.1016/j.ica.2019.118961
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1 Anion Recognition in Aqueous Solution by Cyclic Dinuclear
2 Square Cage-shaped Coordination Complexes
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Cai-Ye Fu, Yu-Qian Li, Lu Chen, Yun-Guang Wang and Li-Rong Lin*
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen,
361005, P. R. China
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ABSTRACT: Three cyclic dinuclear complexes, namely [M2(H2L)2](ClO4)4 [M = Co2+ (1), Ni2+ (2), Zn2+ (3), H2L = (1,2)-bis-N'-(pyridin-2-
ylmethylene)benzohydrazide hydrazine, C26H22N8O2], containing amide and hydrazine groups were synthesized and characterized.
Each central metal ion is coordinated with two oxygen atoms and four nitrogen atoms from carbonyl, and pyridine and imine,
respectively. The metal ion is six-coordinated and has a slightly deformed octahedral geometry. X-ray crystallographic analyses
showed that all the three cyclic dinuclear complexes crystallize in the orthorhombic system, and belong to the C222 space group,
with two molecules in each unit cell. The cyclic dinuclear molecule is linked by two H2L ligands with a Z-form HNNH bridge, nearly
forming a square coordination cage with edges of length around 8.4 Å. The cyclic dinuclear complexes can recognize acetate and
fluoride anions in an acetonitrile solution containing 60% volume water. Recognition is governed by electrostatic interactions in
cooperation with the cage structure effect with the mechanism of anion displacement reaction. The results show that the recognition
of anions in acetonitrile aqueous solution is an exothermic and entropy-reducing reaction. This suggests that the enthalpy change
plays an important role in the presence of highly polar water and highlights the importance of positively charged cage structure
effect. A color change from light yellow to dark yellow was clearly observed for complex 3 on addition of acetate or fluoride anions
in acetonitrile aqueous solution containing 60% water. Complex 3 can be used for colorimetric “naked eye” recognition of acetate or
fluoride anions in acetonitrile aqueous solution. Theoretical calculations based on time dependent density functional theory (TD-
DFT) show the agreement between the theoretical results and experimental data.
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Keywords: Anion recognition; Cyclic dinuclear coordination complexes; Square cage
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1. Introduction
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Anion recognition continues to be one of the most active fields in supramolecular chemistry because of its wide
applications in areas such as sensing, 1-5 extraction, 6, 7 self-assembly, 8-13 transmembrane transport, 14-19 and
catalysis. 20-23 The design of receptors capable of anion binding in aqueous media is a widely researched topic
because the effects of water on the affinities and selectivities of such receptors are still not completely understood.
24-28 Considerable efforts have been made to design various recognition receptors that are effective in water. Such
receptors are mainly based on combinations of non-covalent interactions such as hydrogen-bonding, electrostatic,
π–π, hydrophobic, and coordination interactions. 26, 28-35 Single hydrogen-bonding or other interactions do not
provide efficient receptors for anions in aqueous solution because of competition between the receptor and protic
solvents, particularly water. Protonated bicyclic receptors, 36 quaternary ammonium cages, 37, 38 cyclic or bicyclic
polyamines, 39 cryptands, 40, 41 guanidinium-based receptors, 42 and cyclopeptides43 and other synthetic receptors44, 45
can perform in anion recognition well in aqueous media. Another successful strategy for anion recognition in water
involves the use of metal-based coordination interactions combined with electronic and/or hydrogen-bonding
interactions. 26, 32,43-47 Binding studies performed with these receptors have greatly increased our understanding of
anion coordination chemistry. Thermodynamic studies of anion recognition in water are currently divided into two
main areas: endothermic complexation by a favorable entropy change (positive ΔHО and positive TΔSО) and the
*Corresponding author.
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E-mail address: linlr@xmu.edu.cn

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opposite thermodynamic behavior (i.e., negative ΔHО and negative TΔSО). 24-26 It would be interesting to extend
these investigations to other types of receptor to gain more information on the binding modes that allow anion
recognition in water. On the basis of these reports, we investigated the design of cyclic dinuclear complexes with
molecular cages. Such metal–ligand coordinated molecular cages are potential size- and shape-selective synthetic
receptors with various responses to guest molecules. 48-50 In this study, we designed a ligand containing amide and
hydrazine groups, i.e., (1,2)-bis-N'-(pyridin-2-ylmethylene)benzohydrazide hydrazine (H2L), it generally exists in E-
form (Scheme 1). The oxygen atom from carbonyl and two nitrogen atoms from pyridine and imine can chelate
metal ions. Two Z-form H2L ligands in an HNNH group can easily react with two six-coordinated metal ions to
form a square coordination cage, i.e., [M2(H2L)2]4+, with a saturated coordination metal center. The total four
positive charges on the metal centers make the complex soluble in polar solvents. The cage rim and its cavity
provided by the two H2L ligands is capable of efficient binding of guests. We reasoned that these amide and
hydrazine groups in the positively charged cages could provide the static geometric requirements for specific anion
recognition. The anion recognition properties of pure H2L and its cyclic dinuclear complexes in pure acetonitrile
solution and acetonitrile aqueous solutions containing 40%, 50%, and 60% volume water were therefore
investigated. All three cyclic dinuclear complexes can recognize acetate (CH3COO) and fluoride (F) anions in
acetonitrile solution, even containing 60% water. UV-vis spectroscopy and 1H NMR titrations showed that the
binding force in anion recognition mainly arises from electrostatic interactions in cooperation with the cage
structure effect in acetonitrile aqueous solution. Thermodynamic data showed that anion recognition in acetonitrile
aqueous solution is an exothermic and entropy-reducing reaction. The zinc cyclic complex can be used for
colorimetric “naked eye” recognition of CH3COO  and F anions in acetonitrile aqueous solution.
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2. Experimental Section
2.1 Materials and Methods.
Analytical-grade reagents were purchased from the Sinopharm Chemical Reagent Co. (Shanghai, China) and used
as received. Metal(II) perchlorate hexahydrate [M(ClO4)2·6H2O, M = Co, Ni, Zn] and tetrabutylammonium with
various anions were purchased from Alfa Aesar (Tetrabutylammonium phosphate undergoes protonation (pKa3 =
12.67) in neutral water or aqueous solutions and is identical to tetrabutylammonium hydrogenphosphate). Melting
points were determined with an X-4 micromelting point apparatus without correction. Elemental analyses were
performed with a Vario EL III elemental analyzer. Positive electrospray ionization mass spectrometry (ESI MS) data
were obtained with a Bruker ESQUIRE-3000 Plus LC-MS/MS spectrometer, with methanol as the solvent. IR spectra
(KBr pellets) were recorded with a Nicolet AVATAR FT-IR 330 spectrometer. Solution 1H NMR spectra were recorded
at 400 MHz with a Bruker ADVANCE 400 spectrometer at room temperature, i.e., about 25 °C. The chemical shifts
(ppm) were reported relative to tetramethylsilane as an internal reference. UV-vis absorption spectra were recorded
with a Shimadzu UV224012PC absorption spectrometer. Thermal experiments were performed by placing a 1 cm
cuvette in the thermostated cell of a spectrophotometer, and the spectrum was recorded; the temperature error
was controlled to ±1 °C.
2.2 General Protocol for UV-vis Spectrophotometric Titrations.
The concentrations of stock solutions of H2L and complexes 13 were all 5.0 × 104 mol/L; the solvent was DMSO
or acetonitrile (depending on the solubility of the substance). A microsyringe was used to pipette the stock solution
(50.0 μL) into a 1 cm cuvette containing acetonitrile (2.50 mL) to obtain a 1.0 × 105 mol/L solution for analysis.
Solutions (5.0 × 103 mol/L) of anions as tetrabutylammonium salts were added in microvolumes to the cuvette,
followed by thorough mixing. UV-vis spectra were recorded at each concentration of the added anion.
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2.3 H NMR Titrations.
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Tetrabutylammonium fluoride or acetate was dissolved in 9:1 acetonitrile-d3/DMSO-d6 to prepare a 0.20 mol/L
stock solutions. The host acetonitrile-d3/DMSO-d6 (9:1) solution (0.01 mol/L, 0.50 mL) was added to an NMR tube. A
certain equivalent amount of tetrabutylammonium fluoride or acetate solution was microsyringed into the tube,
followed by thorough mixing. Spectra were recorded at 0, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0 anion
equivalents.
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2.4 DFT and TD-DFT Calculations.
DFT Calculations were performed using Gaussian 09b program.51 The structure of complex 3 was fully optimized
and frequency verifications were performed in acetonitrile using the B3LYP hybrid density functional with the default
PCM solvent model and its crystallographic coordinates. The LANL2DZ basis set was employed for Zn with effective
core potential, and the 6–31ꢀG(d, p) basis set was used for other atoms.52Then the energies of each molecules
were calculated at the optimized geometries by TD-DFT with the same basis set.
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2.5 Determination of [Co2(H2L)2](ClO4)4 (1), [Ni2(H2L)2](ClO4)4 (2), and [Zn2(H2L)2](ClO4)4 (3)
structures.
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Diffraction data for 1 and 3 were collected with a Bruker SMART Apex CCD diffractometer with graphite-
monochromated Mo Kα (λ = 0.71073 Å) radiation in ω scan mode at -100 °C. Crystal data integration and
reduction were performed with SAINT software.53 The data for 2 were collected with an Oxford Gemini S
Ultra CCD area detector at -70 °C. Absorption correction was performed with the multiscan CrysAlis Red
program.54 The structures were solved by direct methods with SHELXS-2014 and refined by full-matrix least-
squares calculations with SHELXL-2014, based on F2.55 All non-hydrogen atoms were refined anisotropically.
Least-squares refinement of hydrogen atoms was mixed: some were constrained and others were
independent. For the constrained case, hydrogen atoms were placed at the calculated positions using the
riding model. Hydrogen atoms in water were not determined. For complexes 2 and 3, the unit cell included
a large region of disordered solvent molecules, which could not be modeled as discrete atomic sites.
PLATON/SQUEEZE was used to remove the diffused electron density from these solvent molecules and to
produce a set of solvent-free diffraction intensities. The generated data were then used to refine the
structures again. Data for the crystal structures of complexes 13 have been deposited at the Cambridge
Crystallographic Data Centre (CCDC 1831733 for 1, 1831731 for 2, and 1831732 for 3).
2.6 Ligand Synthesis.
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2.6.1 (E)-4,4'-Azobenzenedicarboxylic acid diethyl ester (LA).
Ethyl p-aminobenzoate (0.50 g, 3.0 mmol), sodium iodide (0.90 g, 6.0 mmol), and anhydrous ether (30.0
mL) were added to a flask. tert-Butyl hypochlorite (0.66 g, 6.0 mmol) was added and the mixture was stirred
at room temperature for 3 h under nitrogen. Sodium thiosulfate solution (60.0 mL, 1.0 mol/L) was added to
the solution. The aqueous solution was extracted three times with dichloromethane. The combined organic
layers were treated with anhydrous sodium sulfate and filtered. The collected solution was concentrated
under reduced pressure and purified by silica gel chromatography with petroleum
ether/dichloromethane/ethyl acetate (20/10/1) as the eluent. LA (0.34 g, yield 70%) was obtained as an
orange–red solid. mp 135–136 °C; ESI(+) MS m/z (methanol) 327.0 [M+]; 1H NMR (400 MHz, CDCl3) δ (ppm)
8.24 (s, 4H), 8.02 (s, 4H), 4.45 (s, 4H), 1.46 (d, J = 2.9 Hz, 6H).
2.6.2 (E)-1,2-Azodibenzoydrazide (LB).
LA (0.98 g, 3.0 mmol) and hydrazine hydrate (85%, 20.0 mL) were added to a flask. The solution was refluxed
at 110 °C for 10 h under vigorous stirring. Deionized water (50.0 mL) was added to the solution. The mixture
was stored in a refrigerator for 24 h and a pale-yellow solid formed. The precipitate was filtered and washed
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with 1:1 ethanol/water. LB (0.71 g, yield 80%) was obtained as a pale-yellow solid. mp > 300 °C; ESI(+) MS m/z
(methanol) 300.6 [M+]; 1H NMR (400 MHz, DMSO-d6) δ (ppm) 9.39 (s, 2H), 8.21 (s, 2H), 7.63 (d, J = 8.8 Hz, 4H),
6.69 (d, J = 8.8 Hz, 4H), 4.39 (s, 4H).
2.6.3 1,2-Bis-(N'-pyridin-2-ylmethylene)benzohydrazide hydrazine (H2L).
LB (0.30 g, 1.0 mmol) and 2-pyridinecarbaldehyde (0.21 g, 2.0 mmol) were dissolved in methanol (50.0 mL).
The solution was refluxed at 60 °C for 24 h under vigorous stirring. The precipitate was filtered off and washed
with methanol. H2L (0.38 g, yield 70%) was obtained as a yellow solid. mp 189–190 °C; ESI(+) MS m/z
(methanol) 501.0 [M + Na+]; 1H NMR (400 MHz, DMSO) δ (ppm) 11.75 (s, 2H), 8.63–8.58 (m, 2H), 8.45 (d, J =
18.2 Hz, 4H), 7.94 (s, 2H), 7.88 (dd, J = 7.5, 1.3 Hz, 2H), 7.80 (d, J = 8.8 Hz, 4H), 7.40 (ddd, J = 7.3, 4.9, 1.2 Hz,
2H), 6.81 (d, J = 8.8 Hz, 4H); FT-IR (KBr, cm1) 3423 (w, O–H), 1638 (s, C=O), 1571 (m, C=C), 1281 (s, C–N), 829,
782, 758 (m, Ph–H). Anal. Calcd for C26H22N8O2(H2O)4: C, 56.72; H, 5.49; N, 20.35. Found: C, 56.36; H, 5.08; N,
20.36.
2.6.4 Synthesis of Complexes 13.
All three complexes were synthesized by the following method. Ligand H2L (0.048 g, 0.1 mmol) and
M(ClO4)2·6H2O (0.1 mmol, M = Co, Ni, Zn) were dissolved in a mixed solvent (12.0 mL acetonitrile and 8.0 mL
chloroform). The solution was stirred at room temperature for 24 h. Single crystals of complexes 13 were
obtained by anhydrous diethyl ether diffusion into the reaction solution.
[Co2(H2L)2](ClO4)4 (1). Red block crystal (yield 65%); mp >300 °C; ESI(+)-MS m/z (methanol) = 268.7
([Co2(H2L)2]4+), 357.6 ([Co2(H2L)2-H+]3+), 535.9 ([Co2(H2L)2-2H+]2+). FT-IR (KBr, cm1): 3419 (w, OH), 1601 (s,
C=O), 1565 (m, C=C), 1294 (s, CN), 1257 (s, NN), 842, 775, 760 (m, PhH). Anal. Calcd for
Co2C52H44N16O20Cl4(H2O)5(CH3CN)2(CHCl3): C, 38.80; H, 3.49; N, 14.29. Found: C, 39.00; H, 3.41; N, 14.29.
[Ni2(H2L)2](ClO4)4 (2). Yellow block crystal (yield 60%); mp > 300 °C; ESI(+)-MS m/z (methanol) = 268.2
([Ni2(H2L)2]4+), 357.5 ([Ni2(H2L)2-H+]3+), 535.9 ([Ni2(H2L)2-2H+]2+). FT-IR (KBr, cm1): 3434 (w, OH), 1600 (s,
C=O), 1563 (m, C=C), 1293 (s, CN), 1255 (s, NN), 834, 775, 755 (m, PhH). Anal. Calcd for
Ni2C52H44N16O20Cl4(H2O)5(CH3CN)2(CHCl3): C, 38.82; H, 3.49; N, 14.29. Found: C, 38.84; H, 3.35; N, 14.34.
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[Zn2(H2L)2](ClO4)4 (3). Yellow block crystal (yield 65%); mp > 300 °C; ESI(+)-MS m/z (methanol) = 271.8
([Zn2(H2L)2]4+), 361.9 ([Zn2(H2L)2-H+]3+), 542.7 ([Zn2(H2L)2-2H+]2+). 1H NMR (400 MHz, DMSO) δ ppm = 12.08 (s, 2H),
8.60 (d, J = 4.2 Hz, 4H), 8.47 (s, 2H), 7.97 (s, 4H), 7.83 (d, J = 8.5 Hz, 4H), 7.47 (s, 2H), 6.82 (d, J = 8.6 Hz, 4H). FT-IR
(KBr, cm1): 3434 (w, O-H), 1618 (s, C=O), 1571 (m, C=C), 1289 (s, CN), 1255 (s, NN), 834, 773, 708 (m, PhH). Anal.
Calcd for Zn2C52H44N16O20Cl4(H2O)6(CH3CN)2(CHCl3): C, 38.14; H, 3.54; N, 14.04. Found: C, 38.21; H, 3.40; N: 13.96.
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3. Results and Discussion
3.1 X-ray Crystallographic Analysis.
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Crystals of [Co2(H2L)2](ClO4)4 (1), [Ni2(H2L)2](ClO4)4 (2), and [Zn2(H2L)2](ClO4)4 (3) were grown by diethyl ether vapor
diffusion into chloroform and acetonitrile binary solutions. The molecular geometries of their crystal structures were
determined by single-crystal X-ray crystallography. Table 1 gives the crystallographic parameters of the three cyclic
complexes. The important bond lengths and angles of the three compounds are listed in Table S1.
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The perspective view of the molecular structure of complexes 1-3 is shown in Figure 1 and Figures S1-3. The crystal
structures show that the three complexes have similar structures and all belong to the orthorhombic system, in the
C222 space group, and form cationic square shape structures. Each Z-form H2L ligand acts as a bridge between two
metal ions to form two edges, leading to a nearly square coordination cage. The coordination mode of the two central
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metal ions in each complex is the same, i.e., they are coordinated to two oxygen atoms from carbonyl and four
nitrogen atoms from pyridine and imine, forming a stable structure with coordination number six, and the geometry
of the coordination polyhedron is a slightly deformed octahedron. The diagonal M···M separations are 12.878, 12.790,
and 12.923 Å for Co···Co, Ni···Ni, and Zn···Zn, respectively. The average diagonal N4A···N4A (or N5A···N5A) separations
are 11.829, 11.917, and 11.735 Å in complex 1, 2, and 3, respectively. The lengths of the four edges from the metal
center to the first nitrogen atom of the hydrazine group are all around 8.4 Å for the three complexes. This shows that
the three complexes almost form molecular square coordination cages. The total of +4 charges on the metal ions is
balanced by four perchlorate anions outside the cavity of the square. In addition, there are solvent acetonitrile
molecules and water molecules inside the square cavity. The CoO, NiO, and ZnO bond lengths range from 2.112
to 2.146, 2.093 to 2.141, and 2.133 to 2.198 Å, respectively. The CoN, NiN, and ZnN bond lengths are 2.0412.149,
1.9722.108, and 2.0452.141 Å, respectively. These MO and MN bond lengths are similar to those reported in the
literature for the same coordination mode. 56 Furthermore, the hydrogens at the imine carbon, amide nitrogen, and
hydrazine can form intermolecular hydrogen bonds with solvent water molecules or the perchlorate counter anion.
The hydrogen-bond parameters are summarized in Table S2. The crystal structures directly indicate the presence of
multiple hydrogen-bonding sites in this series of cyclic dinuclear square coordination cages.
3.2 UV-vis Spectroscopy Titrations.
The designed H2L ligand has amide CONH and hydrazine HNNH groups (Scheme 1). It normally forms
hydrogen bonds with fluorine, oxygen, or nitrogen atoms, similarly to other neutral anion receptors. First, we
examined the recognition properties of the H2L ligand for anions in organic solvents. The UV-vis absorption
spectra of H2L and H2L with addition of 10 equiv of various anions in acetonitrile solution were recorded.
Figure 2 shows that H2L has a maximum absorption peak at 322 nm ( = 5.9 × 104 L mol1 cm1). The UV-vis
absorption spectrum of H2L changed to different extents on addition of 10.0 equiv of F, CH3COO , Cl, Br,





ClO4 , NO3 , H2PO4 , PO43 HSO4  and BF4 in tetrabutylammonium salts. The clearest change in the UV-vis
absorption spectrum was observed for addition of F. The intensity of the absorption peak at 322 nm
decreased significantly and the peak red shifted. A new absorption peak appeared at 425 nm. Addition of
CH3COO to the H2L solution resulted in a slight increase in the intensity of the absorption peak at 322 nm
and a new absorption peak appeared at 415 nm. Addition of other anions to the H2L solution did not cause
significant changes in the UV-vis absorption spectrum. The inset in Figure 2 shows the changes in the
absorbance at 322 nm after addition of 10.0 equiv of various anions. The intensity changes show that the

order of the degree of interactions between H2L and the anions is F > > CH3COO  > BF4 > Br > ClO4
>
HSO4 > NO3 > PO43 > H2PO4 > Cl. The changes in the UV-vis absorption spectrum of H2L in acetonitrile
solution as a function of F anion concentration were monitored. With increasing addition of F, the intensity
of the absorbance of H2L at 322 nm gradually decreased and red shifted, and a new absorption peak appeared
at 425 nm, with an isosbestic point at 336 nm. These results indicate that H2L forms a stable hydrogen-bonded
complex with F. Similar changes were observed on addition of CH3COO  anion, even on addition of the



strong base OH anion in tetrabutylammonium salt; but other anions, i.e., BF4 , Br , ClO4 , HSO4 , NO3 ,

3
H2PO4 , PO4 and Cl did not change the UV-vis spectrum (Figures S4 and S5 in the electronic supplementary
information). H2L behaves similarly to most neutral anion receptors but does not occur a deprotonation
process; it recognizes anions in pure organic solvents but recognition is poor in solutions containing water
(Figure S6).
H2L reacts easily with Co2+, Ni2+, and Zn2+ to form cyclic complexes 13. These complexes are nearly square
cationic coordination cages, [M2(HL)2]4+, with each Z-form hydrazine of H2L bridging two metal ions to form
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two edges. Unlike H2L, complexes 13 interact strongly with various anions in acetonitrile solution. Taking
complex 3 as an example, Figure 3 shows the changes in the UV-vis absorption spectrum of complex 3 in the
presence of 10 equiv of various anions in acetonitrile solution. The UV-vis spectrum of 3 in acetonitrile
solution shows two strong absorption bands, at 283 nm ( = 3.8 × 104 L mol1 cm1) and 363 nm ( = 1.0 ×
105 L mol1 cm1). The UV-visible absorption spectrum of 3 in acetonitrile changed to different degrees on





addition of 10 equiv of F, Ac, Cl, Br, ClO4 , NO3 , H2PO4  PO43 , HSO4  and BF4 anions in
tetrabutylammonium salts. A comparison of these spectra shows that addition of F and CH3COO  led to red
shifts of both bands, to 302 and 398 nm, with a decrease in the intensity of the shorter-wavelength band and

an increase in the intensity of the longer-wavelength band. In contrast, on addition of PO43 , H2PO4 , Cl,

HSO4  and Br the band at 283 nm red shifted to around 320 nm and its intensity increased, and the intensity


of the band at 363 nm decreased. On addition of ClO4 , NO3  and BF4 anions to the solution, the intensity of
the band at 363 nm decreased. These results show that complex 3 can interact with various anions in
acetonitrile solution. Similar phenomena were observed for complexes 1 and 2 in acetonitrile solution
(Figures S7–S9). It was not observed the occurrence of deprotonation process even for the interaction of
complexes with the strong base OH anion in tetrabutylammonium salt.
These complexes can interact with various anions because the complex cages have an internal cavity with
a cationic charge, and amide and hydrazine multiple recognition sites for anions, therefore the cage complex
can easily interact with anions through electrostatic, hydrophobic, and/or hydrogen-bonding interactions
with anions. It is well-known that the intensity of hydrogen bonding of an anion to a receptor becomes weaker
as the dielectric constant of the solvent increases. 35, 57 Water has one of the highest dielectric constants of
all solvents and different anions show different solvation properties in water.58 We therefore hypothesize
that the three complexes have different binding abilities and will show selectivity for certain anions in solvent
mixtures with high water contents.
The anion recognition abilities of complexes 13 in acetonitrile solutions containing 40%, 50%, and 60%
volume water were therefore examined. The experimental results show that the anion recognition abilities
of the three complexes were similar; complex 3 was selected as an example.
The changes in the UV-vis absorption spectrum of complex 3 on addition of 10 equiv of various anions in
acetonitrile solution containing 40% water (Figure 4) show that the UV-vis absorption spectrum changes most
on addition of CH3COO , with F coming second. On addition of CH3COO  or F, a new absorption peak
appeared at around 380 nm, and the intensity of the absorption peak at 332 nm decreased significantly.
However, addition of other anions did not cause obvious changes to the absorption bands of complex 3.
Complex 3 can selectively recognize CH3COO  and F in acetonitrile solution containing 40% water and





responds little to other anions such as Cl, Br, ClO4 , NO3 , H2PO4  PO43 , HSO4  and BF4 . Figure 5 shows
the changes in the UV-vis absorption spectrum of complex 3 as a function of the CH3COO  anion
concentration in acetonitrile solution containing 40% water. During the titration, a new absorption peak
appeared at 380 nm, accompanied by an isosbestic point at 350 nm; this indicates the formation of stable
complexes of 3 with CH3COO . The changes in the UV-vis absorption spectrum of complex 3 as a function of
the F anion concentration are similar to those with CH3COO  Figure S10.
The changes in the UV-vis absorption spectra of the three complexes on addition of various anions in
acetonitrile solution containing 50% and 60% water were also investigated (Figures S11–19). The results show
that the anion recognition properties are similar to those in acetonitrile solution containing 40% water.
However, the binding ability of the complexes to anions becomes weaker with increasing water content
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because anion solvation becomes easier when more water is present. The hydrogen-bonding interactions
between complexes and anions are generally inhibited, and the recognition ability decreases, with increasing
water content.
On addition of 10.0 equiv of CH3COO  or F the light yellow solution of complex 3 in pure acetonitrile, in
acetonitrile containing 40%, 50%, or 60% water solutions (Figures 6 and S20), all immediately became dark
yellow. However, such color changes for complexes 1 and 2 cannot be observed in acetonitrile containing
40%, 50%, or 60% water solutions (Figure S21). Complex 3 can be used for colorimetric “naked eye”
recognition of acetate or fluoride anions in acetonitrile aqueous solution.
3.3 1H NMR Titrations.
1H NMR spectroscopy is a versatile tool for determining whether interactions between anions and
receptors involve hydrogen bonding or deprotonation of the receptor.59-61 1H NMR spectra of H2L and
complex 3 in the presence of various concentrations of anions were therefore recorded, with 9:1 acetonitrile-
d3/DMSO-d6 as the solvent owing to their solubilities are low in acetonitrile and better in DMSO. Figures 7
and 8 show the corresponding 1H NMR spectra of H2L and complex 3 with various concentrations of CH3COO 
anions in acetonitrile-d3/DMSO-d6 mixed solvents. The chemical shift of Hd (δ, ppm) in the amide group
(CONHd) of H2L is 11.56. This signal gradually broadened and shifted downfield with increasing concentration
of CH3COO −. At the same time, the chemical shift of Ha (δ, 8.03 ppm) in the hydrazine group (NHaNHa) was
broadened and accompanied by a little upfield shift. This shows that Hd and Ha in in H2L complexed with
anions to form hydrogen bonds.
The chemical shift of Hd (δ ppm) in the amide group (CONHd) of complex 3 is 12.03, a little downfield of
that for free H2L, because of coordination of the metal ion with oxygen of the amide group carbonyl, and the
chemical shift of Ha in the hydrazine group (NHaNHa) is the same as that for H2L. The chemical shifts of Hd
in complex 3 became a little narrow on introduction of various amounts of CH3COO . The chemical shift of
Ha (δ, 8.03 ppm) was also broadened and shifted upfield a little. These results show that complex 3 may
interact with anions through Hd or Ha proton in pure organic solvent. Furthermore, the NMR spectrum of
complex 3 with addition of F and CH3COO in acetonitrile-d3 containing of 40% D2O was also examined. The
NMR signals of complex 3 did not change on introduction of these two anions (Figure S22 in the supporting
information). There is therefore no clear evidence of hydrogen bonding in acetonitrile aqueous solution.
The anion may interact with the positively charged square coordination cage by electrostatic interactions in
cooperation with the cage structure effect.
During the NMR titrations in pure acetonitrile-d3 solvent, an orange precipate was observed on addition of a
large excess of anions. The precipate was separated by filtration and its positive electrospray ionization mass
spectrum was examined. The highest peak in the ESI mass spectrum appears at 542.8, corresponding to [Zn2(H2L)2-
2H]2+ , which is the same peak observed in pure complex 3. Addition of F or CH3COO to the complex solution

precipates the similar positively charged cage with a different counter anion. This indicates that ClO4 is probably
displaced by F or CH3COO (inside or outside the cavity) or any complex-anion adduct is formed similar with the
title compound, which leads to the formation of a less soluble positively charged square coordination cage.
However, it can not be excluded that metal ions can be involved in the interaction with the anions although they are
saturated coordination metal centers. At any rate, the complexes are not inert toward ligand substitution and the
“saturated coordination” is reached by involving amide oxygen atom, whose donor properties would be expected to
be weak. Therefore, it can not be ruled out that anions may displace one or more ligand binding sites and directly
interact with metal ions.
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3.4 Enthalpy/entropy Compensation of Complex 3 in Acetonitrile Solutions Containing Water.
Job plots showed that the stoichiometry of H2L binding to F or CH3COO  anions was 1:2, with the
maximum molar fractions at 0.33. The maximum molar fractions in the Job plots for complexes 13 with
F and CH3COO anions are within the range of 0.33 ~ 0.5. (Figure S23) For some supramolecular systems, a
maximum shift to 0.45 may indicate 1:2 complex formation; even more complicated cases are also possible.
62, 63. In the UV-vis spectroscopy titrations, the UV-vis spectrum was unchanged after the ratio of the
concentration of anion to that of receptor molecule reached 2, especially for F as shown in Figure S24.
Therefore our approach was to fit the raw data to 1:2 model and calculated the binding constant between
the receptor and the anion by non-linear fitting of changes in the UV-vis absorption spectra, according to
equation 1. 64
A  (C2  K  A  A ) / (1  C2  K)
(1)
l i m
0
Equation 1 is the non-linear fitting equation for the formation of a 1:2 complex between a receptor molecule and
an anion; A and Alim are the absorbance and maximum absorbance of the new absorption peak in the UV-vis
absorption spectrum of the receptor molecule in the presence of an anion; A0 is the absorbance of the receptor
molecule without an anion; C is the concentration of the receptor molecule; and K is the general binding constant.
The anion concentration was plotted against the absorbance by non-linear fitting to equation 1. The results show
good fitting, which indicates that 1:2 anion complexes are present in the solution (Figure S25). The calculation
results of binding constant (log K) are shown in Table 2.
The anion-binding constants of H2L in pure acetonitrile and of the three complexes in acetonitrile solutions
containing different amounts of water were compared. The results show that the binding constants of the three
complexes with anions in different solutions are almost all greater than those of H2L in pure acetonitrile. This indicates
that the designed cyclic dinuclear complexes easily associate with anions.
A comparison of the anion-binding constants of the complexes in different aqueous solutions shows that the binding
constants decreased with increasing water content. This is mainly because a higher water content enhances anion
solvation by water molecules, therefore the interactions between the receptor molecules and anions are inhibited,
which weakens the ability of the receptors to recognize anions. This further proves that the interactions between the
complex and the anion are mainly caused by electrostatic interactions in cooperation with cage cavity effect.
The mechanism of complex binding with anions in aqueous solutions was elucidated by performing UV-vis titration
spectroscopy of H2L in acetonitrile solution with F, and of complex 3 in acetonitrile containing 40% water with
CH3COO  and F, at 30.0 and 35.0 °C. The effects of temperature on the binding constants can be used to
approximately determine the enthalpy and entropy of the recognition reaction. 65 The data in Table 3 shows that
recognition by H2L of F in acetonitrile solution is an endothermic reaction (∆H > 0) and the entropy is favorable (∆S >
0). As the temperature increases, the change in free energy (∆G) gradually decreases and the reaction at higher
temperatures is favorable for recognition. Similarly, the recognition reactions of complex 3 with F and CH3COO  in
acetonitrile solution are endothermic (∆H > 0), with a favorable entropy term (∆S > 0). As the temperature increases,
∆G gradually decreases and appropriate higher temperatures are beneficial to the recognition reaction. However, the
recognition reaction of complex 3 in acetonitrile containing 40% water is an exothermic reaction (∆H < 0) but with an
unfavorable entropy term (∆S < 0). As the temperature rises, ∆G gradually increases. Higher temperatures are
therefore
unfavorable for anion recognition reactions in aqueous solution. These results show that anion
desolvation plays an important role in anion recognition in pure acetonitrile solvent (the entropy-driven term makes
an important contribution). In contrast, the recognition of anions in acetonitrile aqueous solutions is an exothermic
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and entropy- decreasing reaction. This suggests that the enthalpy change plays an important role in the presence of
highly polar water.
We also tried to determine the binding mode by DFT calculations. The structure of complex 3 was fully optimized
and frequency verifications were performed in acetonitrile using the B3LYP hybrid density functional with the default
PCM solvent model and its crystallographic coordinates. The initial geometry of the fluoride and acetate counter ion
atoms in [Zn2(H2L)2]4+ was retrieved by placing the counter ion atoms on the basis of the optimized structure of the
complex 3. Various starting structures were generated by changing the counter ion position. The possible structures
of [Zn2(H2L)2]F4(I), [Zn2(H2L)2]F4(II), [Zn2(H2L)2] (CH3COO)4, [Zn2(H2L)2] (F)2 (ClO4)2 and [Zn2(H2L)2] (CH3COO)2 (ClO4)2 were
separately calculated and the minimum energy structure was compared with that of [Zn2(H2L)2](ClO4)4. The calculation
results are shown in Table S3. The energy of the optimized structure of complex 3 is the lowest and the [Zn2(H2L)2]F4
complexes is the highest. The energies of [Zn2(H2L)2] (Anion)2(ClO4)2 are between the parent complex 3 and
[Zn2(H2L)2](Anion)4 of which displaces four ClO4 anions. The energy of the complex [Zn2(H2L)2]F4(II) with two fluoride
anions inside its cavity and two outside the cavity is the same as that of [Zn2(H2L)2]F4(I) with all four fluoride anions
outside the cavity. These results indicate that it is possible for the small anion enter the cage cavity. However, the UV-
vis and NMR titration results suggest that the fluoride or acetate anions displace the two counter perchlorate anions
to form a similar cage-like complex. The theoretical UV-vis spectra of the possible structures of [Zn2(H2L)2] (F)2 (ClO4)2
and [Zn2(H2L)2] (CH3COO)2 (ClO4)2 calculated by TD-DFT are the most similar to the experimental spectra of complex 3
on addition of fluoride or acetate anions (see Figure 9). TD-DFT calculations can descript a detail molecular orbitals
involved in the electronic transitions (Table 4). The calculations show that the highest energy occupied orbital (HOMO)
of complex 3 is centered at the two azodibenzoydrazide moieties of the ligands, while the highest energy occupied
orbital (LUMO) localizes on the four N'-pyridin-2-ylmethylene moieties. In case of complexes [Zn2(H2L)2] (F)2 (ClO4)2
and [Zn2(H2L)2] (CH3COO)2 (ClO4)2, HOMO is centered at theπorbital of one of the ligands and their LUMOs are rather
different and complicated (see in Table S4). Furthermore, the HOMO-LUMO energy gap of complexes [Zn2(H2L)2] F2
(ClO4)2 and [Zn2(H2L)2] (CH3COO)2 (ClO4)2 is 3.11 and 3.19 eV, respectively, smaller than that of complex 3 (3.38 eV).
This demonstrates that the interaction of complex 3 with fluoride or acetate anions in aqueous acetonitrile solution
can induce strong changes in its UV-vis spectrum and prove the experimental results.
Some recent reports on the dinuclear metal complexes as chemosensors show that they are excellent hosts toward
certain anions, mainly through metal-ligand interactions, anions include N3 , NCS, Cl, HPO4, nucleoside
monophosphates, oxalate, succinate, and citrate.44,46,47,50, 65-68 Our three cyclic dinuclear complexes are different from
the reported dinuclear metal complexes in that the metal ions in our designed complexes are all six-coordinated, with
normally no more coordinate sites for anions, as in the case for first-row transitional metals. These cyclic dinuclear
complexes can bind strongly with a wide range anions in pure acetonitrile solution. The binding constants with anions
are high of the order 109, i.e., one to three orders higher than most values reported in the literature.46,47,50 They can
identify acetate and fluoride anions in an acetonitrile solution containing 60 % water, but fail to identify certain anion
at higher water contents. We suppose that the enthalpy change plays an important role in the presence of highly polar
water and this highlights the importance of the effects of positively charged cage structures on different anion-binding
abilities.
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4. Conclusions
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In summary, we synthesized three cyclic dinuclear (Co2+, Ni2+, and Zn2+) complexes with square positively charged
cavities. The complexes contained multiple recognition sites, including amide and hydrazine groups. X-ray
crystallographic analyses showed that all three cyclic complexes crystallized in the orthorhombic system, and belonged
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to the C222 space group, with two molecules in each unit cell. The cyclic dinuclear molecule was linked by two Z-form
ligands to form a square coordination cage. The cyclic dinuclear complexes easily associated with various anions in
pure acetonitrile as the solvent, without anion selectivity. The cyclic dinuclear complexes selectively recognized
acetate and fluoride anions in acetonitrile containing 60% water, mainly governed by electrostatic interactions in
cooperation with cage structure effect. The mechanism of anion recognition can be assumed as anion displacement
reaction. TD-DFT calculations show the agreement between the theoretical results and experimental data. Anion
recognition in acetonitrile aqueous solution is an exothermic and entropy-reducing reaction. The enthalpy-driven
change enables effective recognition in the presence of highly polar water. Furthermore, the cyclic binuclear zinc
complex 3 can be used as for colorimetric “naked eye” recognition of acetate or fluoride anions in acetonitrile aqueous
solution.
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We think that such cyclic dinuclear positively charged square coordination cages with appropriate direction NH or
OH groups will provide highly efficient anion recognition in pure water, and we are now investigating the preparation
of more robust similar complexes for anion recognition in water.
385
Acknowledgment
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We are grateful for financial supports from the National Natural Science Foundation of
China (grants no. 21271150).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in the online version, at
http:// doi.org/10.1016/j.ica. xxxxx.
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495
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2191-2194.
(50) V. Amendola, G. Bergamaschi, A. Buttafava, L. Fabbrizzi, E. Monzani, J. Am. Chem. Soc. 132 (2010) 147-156.
(51) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.B. Scalmani, V., B.
Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G.
Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E.
Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant,
S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C.
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Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S.
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12

496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
Scheme, Table, and Figure Captions
Scheme 1. Syntheses of ligands and complexes 13
.
Table 1. Crystallographic data for complexes 13
.
Table 2. Binding constants of compounds with different anions in acetonitrile solutions with various water contents
(logK).
Table 3. Thermodynamic data for anion recognition reactions of H2L and complex 3 in acetonitrile and acetonitrile
containing 40% water.
Table 4. Solvent corrected (acetonitrile) major transition to excited states of complexes with their contributing
excitation, oscillator strengths and associated wavelengths.
Figure 1. Molecular square of complexes 1 (left), 2(middle) and 3(right) (Part hydrogen bonding and solvent
molecules are shown). Color scheme: C gray, O red, N blue, Cl green, Co violet red, Ni sea green and Zn
cyan
Figure 2. Changes in UV-vis absorption spectrum of H2L (1.0 × 105 mol/L) on addition of 10 equiv of different anions
in acetonitrile solution. Inset shows changes in absorbance at 422 nm on addition of 10 equiv of different
anions.
Figure 3. Changes in UV-vis absorption spectrum of complex 3 (1.0 × 105 mol/L) on addition of 10 equiv of different
anions in acetonitrile solution. Inset shows changes in absorbance at 332 nm on addition of 10 equiv of
different anions.
Figure 4. Changes in UV-vis absorption spectrum of complex 3 (1.0 × 105 mol/L) on addition of 10 equiv of different
anions in acetonitrile solution containing 40% water. Inset shows changes in absorbance at 381 nm on
addition of 10 equiv of different anions.
Figure 5. Changes in UV-vis absorption spectrum of complex 3 (1.0 × 105 mol/L) on addition of different
concentrations of acetate in acetonitrile solution containing 40% water.
Figure 6. Color changes of H2L (a and b) and complex 3 (c and d) in presence of various anions: (a) and (c) in pure
acetonitrile solution; (c) and (d) in acetonitrile solution containing 50% water.
Figure 7. 1H NMR spectra of H2L in presence of 0, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 equiv of
CH3COO [nBu4N] in 9:1 acetonitrile-d3/DMSO-d6 solvent.
Figure 8. 1H NMR spectra of complex 3 in presence of 0, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 equiv
of CH3COO [nBu4N] in 9:1 acetonitrile-DMSO-d6 solvent.
Figure 9. UV-vis spectra of the possible structures calculated by TD-DFT and the experimental spectra of complex 3
on addition of fluoride or acetate anions.
13

538
539
540
541
542
543
Scheme 1.
O
N
O
N2, 3h, RT
O
O
O C2H5
H2N
N
NaI, t-BuOCl, Ether
O C2H5
C2H5
( LA )
60 oC, 24h, CH3OH
O
110 oC, 10h
HN
O
HN NH2
NH
N2H4·H2O H2N NH
N
O
( LB )
NH
O
N
N
NH
HN
O
RT, 24h, CH3CN, CHCl3
M(ClO4)2·6H2O
N
HN
N
( H2L )
H
H
N
N
H
N
H
N
N
N
O
O
[M2(H2L)2](ClO4)4
N
N
M

M = Co2+, (1)
Ni 2+, (2)
M
4ClO4
N
N
O
O
Zn2+, (3)
N
N
N
N
H
H
N
N
H
H
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
14

578
579
580
581
582
583
584
585
Table 1.
586
Crystal data
1
2
3
CCDC number
Empirical formula
Moiety formula
1831733
C168H156Cl8Co6N52O70
3(C52H44N16Co2O4),
8(ClO4), 2(C2H6O),
4(C2H3N), 24(O)
4660.62
1831731
C164H144Cl8Ni6N52O74
3(C52H44N16Ni2O4),
8(ClO4), 4(C2H3N),
30(O) [+ solvent]
4663.05
1831732
C164H144Cl8Zn6N52O70
3(C52H44N16O4Zn2),
8(ClO4), 4(C2H3N),
26(O) [+ solvent]
4639.12
Formula weight
Wavelength(Å)
Crystal system
Space group
a (Å)
0.71073
1.54184
0.71073
orthorhombic
C222
orthorhombic
C222
orthorhombic
C222
24.345(3)
28.593(4)
21.598(3)
90
24.320(2)
28.857(2)
21.392(8)
90
24.232(4)
28.447(5)
21.400(4)
90
b (Å)
c (Å)
 (o)
 (o)
90
90
90
 (o)
90
90
90
V (Å3)
15034(3)
2
15013(1)
2
14751(5)
2
Z
Cal density (Mg m-3)
Abs coefficient (mm-1)
θ range
1.030
1.029
1.044
0.463
1.663
0.622
1.424 to 28.401
66582
3.063 to 61.999
15329
1.457 to 28.532
65256
Reflections collected
Data/restraints/para
Goodness of fit on F2
Final R indexes [I>=2σ(I)]
17951/0/701
0.810
10398/0/695
0.981
17663/6/680
0.835
R1 = 0.0623
WR2 = 0.1513
R1 = 0.1028
WR2 = 0.1593
R1 = 0.0732
WR2 = 0.1958
R1 = 0.0881
WR2 = 0.2126
R1 = 0.0579
WR2 = 0.1460
R1 = 0.0972
WR2 = 0.1541
R indices [all data]
587
588
589
590
591
592
593
594
15

595
596
597
598
599
600
601
602
Table 2

CH3COO F
Cl
H2PO4
Br

Compounds
H2L (0%)
1 (0%)
7.93
9.83
9.46
9.36
9.37
9.15
7.95
9.46
9.32
9.07
8.38


10.22
9.23
9.16
10.11
9.37
7.04
9.79
9.22
8.68
8.34 7.32

1 (40%)
1 (60%)
2 (0%)









7.74

9.63

2 (40%)
2 (60%)
3 (0%)


9.01 9.31
9.60

3 (40%)
3 (60%)





603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
(The relative uncertainty was less than 10%.)
16

637
638
639
640
641
642
643
644
645
Table 3
Anion
F
CH3COO
∆G
∆H
∆S
∆G
∆H
∆S
Compounds
T (oC)
(KJ/mol)
(KJ/mol)
(KJ/mol·K)
(KJ/mol)
(KJ/mol)
(KJ/mol·K)
25.0
30.0
35.0
25.0
30.0
35.0
25.0
30.0
35.0
-47.8
-49.4
-51.4
-55.8
-60.4
-63.1
-52.6
-50.2
-45.3
H2L
60.9
0.36
0.72
-0.73



(acetonitrile)
-53.9
-57.6
-59.7
-53.2
-42.0
-38.2
3
160.7
-271.2
117.4
-497.4
0.57
-1.50
(acetonitrile)
3
(40% water)
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
17

669
670
671
672
673
Table 4
Complexes/No. Wavelength (nm) Osc. Strength Symmetry Major contribs
[Zn2(H2L)2] (ClO4)4 /
1
2
3
4
5
6
7
8
9
409
399
386
383
321
318
311
309
298
1.1883 Singlet-A H-1->LUMO (61%), HOMO->L+1 (10%), HOMO->L+2 (19%)
0.3167 Singlet-A H-1->L+3 (72%), HOMO->L+1 (16%)
0.2703 Singlet-A H-3->L+1 (30%), H-2->LUMO (56%)
0.1788 Singlet-A H-3->L+1 (19%), H-3->L+2 (14%), H-2->LUMO (30%), H-2->L+3 (30%)
0.1483 Singlet-A H-5->L+1 (42%), H-4->LUMO (43%)
0.2770 Singlet-A H-5->L+2 (40%), H-4->L+3 (37%)
1.2244 Singlet-A H-7->LUMO (38%), H-6->L+1 (26%
0.5227 Singlet-A H-7->L+3 (40%), H-6->L+1 (14%), H-6->L+2 (32%)
0.1202 Singlet-A H-9->LUMO (26%), H-9->L+3 (11%), H-8->L+2 (28%)
[Zn2(H2L)2] F2 (ClO4)2 /
1
2
3
4
5
6
7
8
9
415
404
399
393
386
383
379
337
336
0.6329 Singlet-A HOMO->L+2 (70%), H-1->L+3 (11%)
1.0223 Singlet-A H-2->LUMO (76%)
0.3442 Singlet-A HOMO->L+2 (10%), HOMO->L+3 (87%)
0.1555 Singlet-A
0.2218 Singlet-A
H-2->L+1 (88%)
H-1->L+2 (64%), H-1->L+3 (24%), HOMO->L+2 (11%)
0.1456 Singlet-A H-1->L+2 (31%), H-1->L+3 (63%)
0.1111 Singlet-A
0.1561 Singlet-A
H-4->LUMO (10%), H-3->LUMO (48%), H-3->L+1 (23%)
H-5->L+2 (22%), H-5->L+3 (22%), H-4->L+2 (51%)
0.104
Singlet-A
H-5->L+2 (29%), H-4->L+3 (57%)H-5->L+3 (9%)
10 313
0.2126 Singlet-A
H-13->L+2 (11%), H-12->L+2 (10%), H-12->L+3 (41%), H-7->LUMO (13%)
11 312
12 310
13 300
0.5705 Singlet-A
0.3014 Singlet-A
0.2969 Singlet-A
H-12->L+3 (13%), H-7->LUMO (25%), H-6->L+1 (17%)
H-7->LUMO (28%), H-6->LUMO (14%), H-6->L+1 (34%)
H-1->L+7 (18%), HOMO->L+6 (58%), HOMO->L+7 (15%)
[Zn2(H2L)2] (CH3COO)2 (ClO4)2 /
1
2
3
4
5
6
7
8
9
415
407
401
393
388
384
317
312
310
0.2561
0.5297
Singlet-A HOMO->L+2 (69%), HOMO->L+3 (11%)
Singlet-A H-2->LUMO (62%), H-2->L+1 (15%), HOMO->L+2 (10%)
0.8009 Singlet-A
0.2555 Singlet-A H-2->LUMO (20%), H-2->L+1 (70%)
0.3579 Singlet-A H-1->L+2 (78%), HOMO->L+3 (16%)
HOMO->L+2 (15%), HOMO->L+3 (67%)
0.1465 Singlet-A H-4->LUMO (86%)
0.3021 Singlet-A H-8->L+2 (77%), H-7->L+2 (11%)
0.7559 Singlet-A H-11->LUMO (27%), H-9->L+1 (49%)
0.2816 Singlet-A H-11->LUMO (52%), H-9->L+1 (31%)
674
675
676
677
678
679
680
681
682
683
684
685
Figure 1.
18

686
687
688
689
690
691
692
693
Figure 2.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.20
0.15
0.10
0.05
BF4
Br
CH3COO
ClO4
Cl
NO3
ClO4
CH3COO F
0.00
BF4
F
PO4
Br
Cl
HSO4
H
2PO4
H2PO4
Anion
HSO4
NO3
PO4
H2L
250
300
350
400
450
500
550
600
Wavelength/nm
694
695
696
697
698
Figure 3.
699
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
H2PO4
F
HSO4
BF4
Br
ClO4
Cl
NO3
CH3COO
PO4
0.8
0.6
0.4
0.2
NO3
ClO4
CH3COO F
0.0
BF4
PO4
Br
HSO4
Cl
H2PO4
Anion
Complex 3
250
300
350
400
450
500
550
600
Wavelength / nm
700
701
702
703
704
705
706
707
19

708
709
710
711
712
713
Figure 4.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
CH3COO
F
H2PO4
0.8
0.6
0.4
0.2
HSO4
NO3
ClO4
Br
Cl
CH3COO F
0.0
BF4
PO4
Br
Cl
BF4
HSO4
H
2PO4
Anion
NO3
ClO4
PO4
Complex 3
250
300
350
400
450
500
550
600
Wavelength/nm
714
715
Figure 5.
716
[CH3COO ], 105mol/L
0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.4
1.0
1.4
2.0
2.4
3.0
3.4
4.0
4.4
5.0
5.4
6.0
6.4
7.0
8.0
9.0
10
250
300
350
400
450
500
Wavelength / nm
717
718
719
720
721
722
723
724
725
726
727
728
729
730
20

731
732
733
734
735
736
737
738
739
Figure 6.
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
21

764
765
766
767
768
769
770
771
772
773
Figure 7.
.
~
Chemical shift (p
774
775
776
777
Figure 8.
~
778
779
780
781
782
783
784
785
22

786
787
788
789
790
791
792
793
Figure 9
794
[Zn2(H2L)2](ClO4)4
Calculated
120000
100000
80000
60000
40000
20000
0
[Zn2(H2L)2]F4
[Zn2(H2L)2](CH3COO)4
[Zn2(H2L)2](ClO4)2F2
[Zn2(H2L)2](ClO4)2(CH3COO)2
250
300
350
400
400
450
450
500
550
600
2.0
1.5
1.0
0.5
0.0
[Zn2(H2L)2](ClO4)4
[Zn2(H2L)2](ClO4)4+ 10 equv F
Experimental
-
-
[Zn2(H2L)2](ClO4)4 + 10 equv CH3COO
250
300
350
500
550
600
Wavelength / nm
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809 Anion Recognition in Aqueous Solution by Cyclic Dinuclear
810 Square Cage-shaped Coordination Complexes
811
812
813
814
Cai-Ye Fu, Yu-Qian Li, Lu Chen, Yun-Guang Wang, and Li-Rong Lin*
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen,
361005, P. R. China
23

815
816
817
818
Research Highlights
819
820
821
822
823
824
825





Three new macrocyclic dinuclear complexes, containing amide and hydrazine groups were synthesized and characterized.
The macrocyclic dinuclear molecule is a square cage with edges of length around 8.4 Å.
The complexes can recognize acetate and fluoride anions in an acetonitrile solution containing 60% volume water.
The anion recognition is through exothermic and entropy-reducing reactions.
The dinuclear zinc(II) complex can be used for colorimetric “naked eye” recognition of acetate or fluoride anions.
24