Arene-based Ligand Research Articles

A new thiacalix[4]arene-based metal-organic framework as an efficient electrochemical sensor for trace detection of Cd2+ and Pb2+

Heavy metal ions (HMIs) can lead to serious harm to human health and ecological environment. Thus, developing an efficient detection method for HMIs is extremely necessary. Herein, a new thiacalix[4]arene-based metal–organic framework (MOF) [Co2(L1)(TPA)2]·DMA·3CH3OH·H2O (Co-LTPA) (L1 = thiacalix[4]arene-based ligand and H2TPA = terephthalic acid) was successfully synthesized. The electrochemical detection platform (Co-LTPA/GCE) was acquired, and Co-LTPA/GCE featured ultrasensitive detection of HMIs with greatly low limits of detection (LODs) of 0.119 nM for Cd2+ and 0.279 nM for Pb2+ as well as wide linear ranges of 0.08–5.8 μM for Cd2+ and 0.01–6.0 μM for Pb2+. More importantly, the Co-LTPA/GCE sensor was employed to detect foods (milk, honey and orange juice) and water samples (tap water, lake water and drinking water) with satisfactory recoveries, proving the sensor reliability in practical applications. This work provided an example that the functional electrochemical Co-LTPA/GCE sensor was employed for Cd2+ and Pb2+ detection.

A new polyoxometalate-resorcin[4]arene-based framework as an efficient anode material for lithium-ion batteries

Abstract The development of new and efficient anode materials for lithium-ion batteries (LIBs) has attracted considerable attention. Herein, a new polyoxometalate-based metal-organic framework (POMOF), [Mn4(L)(SiW12O40)·(DMF)2·(H2O)6]·4OH·4DMF·7H2O (1), was prepared with a resorcin [4]arene-based ligand (L), Keggin-type [SiW12O40]4- anion and Mn(II) cation (DMF = N,N′-dimethylformamide). Compound 1 has a layer structure sandwiched by [SiW12O40]4- anions. The high specific capacity and excellent cycling stability are achieved by using 1 as an anode material for LIBs. The high electrochemical performance of compound 1 is attributed to the good electron storage and reversible multi-electron redox properties of [SiW12O40]4- anions within the framework.

Resorcin[4]arene-based cadmium(II) coordination polymers for efficient luminescent detection of Fe3+ and Cr2O72− ions

Two luminescent cadmium(II) coordination polymers, [Cd2(L)(BDC)2]·3DMF·5EtOH (1) and [Cd2(L)(OH-BDC)2]·2DMF·6MeOH (2), have been solvothermally prepared with resorcin[4]arene-based ligand (L) and dicarboxylic acids (H2BDC = isophthalic acid, OH-H2BDC = 5-OH-isophthalic acid and N,N′-dimethylformamide). 1 and 2 are isostructural and feature fascinating layer structures. Remarkably, 1 and 2 showed intense luminescent properties and were used as highly efficient multiple luminescent detection for Fe3+ and Cr2O72− ions.

Synthesis and Binding Properties of a Tren-Capped Hexahomotrioxacalix[3]arene.

The straightforward synthesis of a new hexahomotrioxacalix[3]arene-based ligand capped by a tren subunit was developed and the binding properties of the corresponding zinc complex were explored by NMR spectroscopy. Similarly to the closely related calix[6]tren-based systems, the homooxacalixarene core ensures the mononuclearity of the zinc complex and the metal center displays a labile coordination site for exogenous guests. However, very different host-guest properties were observed: i) in CDCl3 , the zinc complex strongly binds a water molecule and is reluctant to recognize other neutral guests, ii) in CD3 CN, the exo-coordination of anions prevails. Thus, in strong contrast to the calix[6]tren-based systems, the coordination of neutral guests that thread through the small rim and fill the polyaromatic cavity was not observed. This unique behaviour is likely due to the fact that the 18-membered ethereal macrocycle is too small to let a molecule threading through it. This work illustrates the key role played by the second coordination sphere in the binding properties of metal complexes.

Metal ion induced single-crystal-to-single-crystal transformation and luminescent sensing properties of resorcin[4]arene-based metal–organic frameworks

In this work, two new resorcin[4]arene-based metal–organic frameworks (MOFs), namely, [(CH3)2NH2][Zn3(HL)(L)(DMF)(H2O)2]·2H2O (1-Zn) and [(CH3)2NH2]2[Cd3(L)2(H2O)4]·2DMF·2H2O (2-Cd), have been synthesized under solvothermal conditions (H4L represents the resorcin[4]arene-based ligand). 1-Zn exhibits a layer structure, while 2-Cd shows a 3D motif. Remarkably, by immersing 1-Zn in an aqueous solution of Cu2+ ions, a new Cu(II)-MOF [Cu2(H2L)2(H2O)2]·3.5H2O (1-Cu) was achieved via a metal ion induced single-crystal-to-single-crystal (SCSC) transformation manner, involving generation of new metal-O bond and change of metal ion coordination geometry. Moreover, luminescent detection properties for Fe3+ ions and Cr2O72− ions were also investigated with 1-Zn and 2-Cd as luminescent sensors.

A Planar-Chiral Pillar[5]arene-Based Monophosphine Ligand with Induced Chirality at the Biaryl Axis

A planar-chiral pillar[5]arene with cyclohexylmethoxy side chains and a pendant diphenylphosphine was prepared and used as a chiral ligand in asymmetric reactions. Chirality transfer from the planar-chiral pillar[5]arene scaffold to the chiral biaryl moiety was demonstrated by circular dichroism (CD) spectroscopy, single-crystal X-ray diffraction analysis, and asymmetric catalysis.

Highly Stable Copper(I)-Based Metal-Organic Framework Assembled with Resorcin[4]arene and Polyoxometalate for Efficient Heterogeneous Catalysis of Azide-Alkyne "Click" Reaction.

A new highly stable copper(I)-based metal-organic framework (MOF), namely, [CuI4(SiW12O40)(L)]·6H2O·2DMF (1), was synthesized by incorporating Keggin-type polyoxometalate (POM) anions and a functionalized wheel-like resorcin[4]arene-based ligand (L) under sovothermal condition. 1 exhibits a charming 3D supramolecular architecture sandwiched by the POM anions. Noticeably, 1 has exceptional chemical stability, especially in organic solvents or aqueous solutions with a wide range of pH values. Considering the catalytically active Cu(I) sites in 1, the azide-alkyne cycloaddition (AAC) reaction was studied by employing 1 as the heterogeneous catalyst. Most strikingly, 1 exhibits excellent catalytic activity as well as recyclability for the AAC reaction.

"Two-Story" Calix[6]arene-Based Zinc and Copper Complexes: Structure, Properties, and O2 Binding.

A new "two-story" calix[6]arene-based ligand was synthesized, and its coordination chemistry was explored. It presents a tren cap connected to the calixarene small rim through three amido spacers. X-ray diffraction studies of its metal complexes revealed a six-coordinate ZnII complex with all of the carbonyl groups of the amido arms bound and a five-coordinate CuII complex with only one amido arm bound. These dicationic complexes were poorly responsive toward exogenous neutral donors, but the amido arms were readily displaced by small anions or deprotonated with a base to give the corresponding monocationic complexes. Cyclic voltammetry in various solvents showed a reversible wave for the CuII/CuI couple at very negative potentials, denoting an electron-rich environment. The reversibility of the system was attributed to the amido arms, which can coordinate the metal center in both its +II and +I redox states. The reversibility was lost upon anion binding to Cu. Upon exposure of the CuI complex to O2 at low temperature, a green species was obtained with a UV-vis signature typical of an end-on superoxide CuII complex. Such a species was proposed to be responsible for oxygen insertion reactions onto the ligand according to the unusual and selective four-electron oxidative pathway previously described with a "one-story" calix[6]tren ligand.

A Family of Metal–Organic Frameworks with a New Chair-Conformation Resorcin[4]arene-Based Ligand: Selective Luminescent Sensing of Amine and Aldehyde Vapors, and Solvent-Mediated Structural Transformations

By utilizing a new chair-conformation resorcin[4]arene-based octacarboxylate ligand, four functional metal–organic frameworks (MOFs), namely, [(CH3)2NH2]4[Cd2(L)]·4H2O (1), [(CH3)2NH2]4[Zn2(L)]·2DMF·6H2O (2), [(CH3)2NH2]4[Co2(L)]·2DMF·4H2O (3), and [(CH3)2NH2]2[Co3(L)(H2O)12] (4) (H8L = 2,8,14,20-tetra-methylphenyl-4,6,10,12,16,18,22,24-octa-carboxymethoxy-resorcin[4]arene and DMF = N,N-dimethylformamide), were solvothermally synthesized and structurally characterized. In 1, each L8– anion bridges eight Cd(II) atoms to give a three-dimensional (3D) (4,8)-connected (46)(412.610.86) framework. In isostructural 2 and 3, each L8– anion links eight adjacent Zn(II) or Co(II) atoms to yield a 3D (4,8)-connected (46)(411.612.85) net. In 4, each L8– anion only bridges four Co(II) atoms by using its four carboxylates each in a monodentate coordination mode to generate an infinite one-dimensional (1D) chain. Remarkably, the highly selective luminescent sensing of amine and aldehyde vapors was studied for 1 and 2 as ...

Extraction properties of tetraheptylresorcin[4]arenes in relation to Cr(III) ions

Resorcin(4)arene-based ligand bearing four heptyl chains at the lower rim of the molecule was prepared and modified by four tetradietoxyphosphoryl groups in the upper rim. The compounds obtained were characterized by NMR spectroscopy and their extractability toward chromium(III) ions was studied. The influence of process parameters such as the pH of aqueous phase, agitation time and also extractant's structure and concentration on efficiency of Cr(III) ions solvent extraction is presented. The highest yield of Cr(III) solvent extraction was obtained for two-hour agitation time of 5.010 −4 M metal solution of pH 5.0 and 5.010 −3 M chloroform solution of the tetradietoxyphosphorylated derivative of heptyl- resorcin(4)arene. Under optimal conditions, competitive solvent extraction of Cr(III), Zn(II), and Cd(II) ions was performed and separation factor values were established as 77.0 and 24.9 for Cr(III)/Cd(II) and Cr(III)/Zn(II) ions pairs, respectively. The stoichiometry of formed metal-ligand complexes 1:1 was found by classical slope analysis method.

A Water-Soluble Calix[4]arene-Based Ligand for the Selective Linear Coordination and Stabilization of Copper(I) Ion in Aerobic Conditions

A number of serious diseases are linked to copper homeostasis dysfunction. The design of copper(I)-selective chelators is of particular interest not only for the creation of therapeutic objects but also as useful tools to gain insights into the coordination of copper(I) in a biological medium. A water-soluble Cu(I)-selective ligand that associates strong Cu(I) binding at pH = 7.4 (10(14) M(-1)), insensitivity to air, and selectivity toward Cu(II) and other biologically relevant cations is described.

Tb(3+)-triggered luminescence in a supramolecular gel and its use as a fluorescent chemoprobe for proteins containing alanine.

A tetracarboxylic acid-appended thiacalix[4]arene-based ligand with Tb(3+) formed a supramolecular gel which showed novel fluorogenic sensor capability for probing alanine and proteins containing alanine.

Tetrapyrazolyl-calix[4]arene-based supramolecular architectures from [Pd16L4] macrocycle to three-dimensional microporous channels

By employing di-palladium complex [(bpy)2Pd2(NO3)2](NO3)2 (where bpy=2, 2′-bipyridine) as corners and tetrapyrazolate calix[4]arene-based ligand (L4−) as linkers, a novel cavity-containing high-positively-charged polypyrazolate-bridged metallo-macrocycle [Pd16L4]16+·16NO3 with Pd(II)⋯Pd(II) dimetal-coordination motifs has been synthesized by a directed coordination driven self-assembly with spontaneous deprotonation of the 1H-bipyrazole ligands in aqueous solution. The counter ions NO3− were trapped within the amphiphilic 3-D microporous channels in the solid state.

Synthesis, crystal structure and copper complex of 1,3-alternate p-tert-butylthiacalix[4]arene 2-picolyl schiff base

A p-tert-butylthiacalix[4]arene-based polydentated ligand with four Schiff base units on 1,3-alternate position at lower rim has been prepared in three steps, which coordinated to copper ion to form a novel dicopper complex. The structures of the polydentated thiacalixarene ligand and copper complex were fully characterized by spectroscopy and X-ray single crystal diffraction method.

Synthesis and metal ion extraction of calix[4]arene mono- and diacids with 2-methoxyethoxy pendant groups

A mono-ionizable calix[4]arene-based ligand with three 2-methoxyethoxy pendant groups is synthesized. A di-ionizable analogue with two 2-methoxyethoxy pendant groups is also prepared. Competitive solvent extractions of alkali metal cations and of alkaline earth metal cations by these ligands are performed, as are single species extractions of Hg2+ and of Pb2+. The number of proton-ionizable groups in the ligand is found to influence the metal ion binding behavior.

Unusually Large Bite Angle of a Distally Diphosphanylated Calix[4]arene Chelator (Eur. J. Inorg. Chem. 31/2010)

The cover picture shows the structure of a calix[4]arene-based ligand with an unusually large bite angle. Calix[4]arenes constitute versatile macrocyclic compounds, which can be obtained by condensation of phenols with formaldehyde. The so-called CALDIPs, which are diphosphanes built upon such a skeleton, have recently found applications in a variety of C–C bond-forming reactions, including polymerisation reactions. In the presence of group 8–10 transition metals, CALDIP ligands form straightforwardly dynamic chelate complexes, in which the ligand bite angle undergoes periodic variation. In the article by C. Jeunesse, D. Matt et al. on p. 4917 ff, a new chelate complex is described in which a CALDIP ligand adopts an unexpectedly large bite angle of 139°, which thus illustrates the great flexibility of the calix[4]arene core. The key ligand is depicted as superimposed over the sky of Strasbourg city (photo courtesy of Dr. R. Ruppert, UdS). Phenol–formaldehyde condensation products were already synthesised in Strasbourg by A. Baeyer in 1872.

First ZnII Bowl-Complexes Modeling the Tris(histidine) Metallo-Site of Enzymes

The bowl-shaped resorcin[4]arene-based ligand was prepared as a model of the trihistidine coordination core present in many mononuclear metalloenzymes. The -CH(2)-O-CH(2)- linkers connecting the imidazoles to the cavity allow three imidazoles to simultaneously bind a metal ion, and favor cis-coordination of two exchangeable ligands. The corresponding mononuclear Zn(II) complexes were shown to be capable of the selective guest binding and exchange at both endo and exo positions.

Calix[4]arene-based ligands as endotoxin receptors

Three new calix[4]arene-based receptors as potential antimicrobial agents have been synthesized. Their recognition ability towards lipopolysaccharides of Gram-negative bacteria has been studied by NMR and UV titrations.

First Insights into the Electronic Properties of a Cu(II) Center Embedded in the PN3 Cap of a Calix[6]arene-Based Ligand

The first metal complex based on the calix[6]PN3 cryptand is described. The solid-state and solution studies show a 5-coordinate Cu(II) center due to its coordination to the PN3 cap and to an exchangeable guest molecule. Spectroscopic and electrochemical studies evidence surprising properties of the metal ion, which are tentatively assigned to the unusual P-Cu(II) bond enforced by the cryptand.

Supramolecular Assemblies with Calix[6]arenes and Copper Ions: from Dinuclear to Trinuclear Linear Arrangements of Hydroxo−Cu(II) Complexes

Complexation of copper(II) by calix[6]arene-based ligands bearing either two or three N-benzylimidazole coordinating arms under basic conditions has been studied. Whereas the tris(imidazole) derivative stabilizes dicationic 5-coordinate aqua complexes in a mononuclear state with an intracavity bound guest, in the presence of hydroxide ions, the latter undergo dimerization. An X-ray structure revealed decoordination of one imidazole arm and formation of a bis(hydroxo) bridged Cu(II) core with a square-planar geometry for both metal centers sandwiched by two empty calixarene cavities. Upon methanolysis, the dinuclear complex underwent an unexpected rearrangement leading to the clean formation of a trinuclear complex. X-ray diffraction analyses of this novel species revealed a trinuclear core constructed around a central Cu(II) ion that is doubly bridged through either methoxide or hydroxide anions to two Cu(II) ions hold by two calixarene units. The same complex could be directly synthesized by reacting the ligand with copper(II) perchlorate in a 2:3 ratio in the presence of base. In solution, the tetrahydroxo Cu(3) complex was characterized by UV-vis and (1)H NMR spectroscopies and displayed an electron paramagnetic resonance (EPR) signal only below 100 K that accounts for a S = 1/2 fundamental state. Formation of the same di- and trinuclear species was observed with a calix[6]arene-based bis(imidazole) ligand, which demonstrates the generality of the reaction schemes. All these results emphasize the versatility of the calix[6]arene scaffold for the stabilization of metal complexes with various nuclearities.