Complexation and DFT studies of lanthanide ions by (2-pyridylmethoxy)homooxacalixarene derivatives

The binding of lanthanide cations by 2-pyridylmethoxy derivatives of p-tert-butyldihomooxacalix[4]arene (1b), in the cone conformation, and p-tert-butylhexahomotrioxacalix[3]arene (2b), in both cone and partial cone conformations, was studied. These properties were assessed by extraction studies of the metal picrates from water into dichloromethane and stability constant measurements in methanol and acetonitrile, using spectrophotometric and microcalorimetric techniques. Proton NMR titrations with La³⁺ and Yb³⁺ cations were done in order to get information on the binding sites. Computational methods (density functional theory (DFT) calculations) were also used to complement the NMR data. The p-tert-butylcalix[4]arene analogue (3b) was also studied, and the results of the four ligands were compared. Partial cone-2b is the best extractant for lanthanide ions, showing some preference for the heavy lanthanides. In complexation, all four ligands show the same trend and a high selectivity for Yb³⁺ (ML, log β ≥ 7). Besides the formation of ML complexes, ML₂ species were also obtained. In most cases, these species were corroborated by the proton NMR studies. For partial cone-2b with Pr³⁺ the complexation process is enthalpically driven, whereas for 3b the formation of the ML₂ species with this cation is due to a favourable entropy term. DFT studies indicate that ligand 3b forms the most stable complex with La³⁺, followed by partial cone-2b.     

p-tert-Butyldihomooxacalix[4]arene/p-tert-Butylcalix[4]arene: Transition and Heavy Metal Cation Extraction and Transport Studies by Ketone and Ester Derivatives

The binding properties of two phenylketones (2a and 3a) and two ethylesters (2b and {3b) derived from p-tert-butyldihomooxacalix[4]arene or from p-tert-butylcalix[4]arene, in the cone conformation, towards transition (Ag⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn²⁺, Fe²⁺ and Mn²⁺) and heavy (Cd²⁺, Hg²⁺ and Pb²⁺) metal cations have been determined by extraction studies with metal picrates and liquid membrane transport experiments with the same salts. The affinity of these ligands for Ag⁺ has also been investigated by ¹H NMR spectroscopy. Both ketones are better extractants than the esters, and show a strong preference for Ag⁺, while Cu²⁺ is the most extracted cation with the esters. ¹H NMR titrations with AgSO₃CF₃ indicate 1 : 1 complexes for all ligands, those with ketones are more stable, on the NMR time scale, than those with esters. Both esters are good carriers for Ag⁺, and 2b exhibits the highest transport rate (4.7 mol h^-1) found until now with dihomooxacalix[4]arene derivatives.     

Excellent Ag+ selective receptors: Syntheses and complexation properties of novel biscalix[4]arene with benzalazine groups

By reacting mono-substituted or 1,3-bi-substituted [2-(p-formylphenyloxy)ethyloxy]-p-tert-butylcalix[4]arene (3 or 4) with hydrazine hydrate in ‘1+2’ or ‘2+2’ condensation mode, novel benzalazine-bridging biscalix[4]arenes 5 and 7 were conveniently obtained in the yields of 76 and 81%, respectively. Condensation of compound 4 and salicylide hydrazone gave a novel calix[4]arene benzalazine derivative 6 in the yield of 85%. The structures and conformations of all new compounds were characterised by elemental analyses, ESI-MS, ¹H NMR and ¹H–¹H COSY techniques. Biscalix[4]arene 7 adopts a symmetrical cone conformation with tube cavity. The liquid–liquid extraction experiment showed that all new hosts possessed excellent complexation abilities towards soft metal cations. Compound 7 exhibited high complexation selectivity towards Ag⁺. The Ag⁺/Na⁺ and Ag⁺/Hg²⁺ extraction percentages of host 7 were as high as 73.1 and 54.9, respectively. The UV–vis spectra complexation experiments revealed that the complexation constant of receptor 7 with Ag⁺ was 1.9 × 10⁵ M^? 1 and the 1:1 stoichiometry of receptor 7–Ag⁺ complex was formed. The ¹H NMR spectra complexation experiments suggested that Ag⁺ was bound in a cavity composed of two benzalazine groups on bridging chains.     

一种基于硫杂杯[4]芳烃的高效银离子载体

合成了基于下缘含有酰肼基团的硫杂杯芳烃衍生物的银离子载体1,其核磁研究证实硫杂杯芳烃以1,3-交替构象存在,并且通过非竞争萃取实验和竞争萃取实验研究了它对碱金属和过渡金属离子（Li⁺, Na⁺, K⁺, Cs⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Ag⁺）的键合能力和选择性。实验结果表明：将酰肼基团引入1,3-交替构象的硫杂杯芳烃骨架的下缘可以提高其对Ag⁺的键合能力和选择性,同时,对Cu²⁺的萃取能力较弱,对碱金属离子和其它的重金属离子几乎没有萃取能力。进一步的核磁滴定和电喷雾质谱实验显示化合物1与银离子形成配合物的配合计量比为1：1,由此推断主要由“N-Ag⁺”配位键以及硫杂杯芳烃骨架的协同作用构成了化合物1与银离子的配合模式。     

Novel calix[4]arene-thiacrown ether for selective and efficient extraction of Ba(II), Pb(II), and Hg(II)

A di-ionizable p-tert-butylcalix[4]arene-1,3-thiacrown-5 ether extractant was synthesized. Its cone conformation and polyether ring attachment regioselectivity were verified by NMR spectroscopy. The metal ion-complexing properties of this ligand were evaluated by solvent extractions of metal cations from aqueous solutions into chloroform. The ligand was found to be an efficient extractant with Ba²⁺ selectivity in competitive solvent extraction of alkaline earth metal cations. It also exhibits high extraction ability for Pb²⁺ and for Hg²⁺ in single species solvent extractions.     

BODIPY appended cone-calix[4]arene: selective fluorescence changes upon Ca binding

BODIPY appended new calix[4]arene diethyl ester (1) has been synthesized in the cone conformation. With respect to fluorescence intensity changes upon metal ion complexation, 1 shows a Ca²⁺ ion selectivity over other metal cations. Presence of two proximal hydroxyl groups and two facing ethyl esters in BODIPY-calix[4]arene were observed to play an important role in exhibiting its selective Ca²⁺ ion binding.     

Experimental and computational studies of the binding properties of lower rim tetra- and di-substituted calix[4]arene amide derivatives with metal ions

Abstract

Experimental and theoretical binding studies of representative alkali, alkaline earth, transition, heavy metal and lanthanide cations by tetra- and di-substituted calix[4]arene amide derivatives (diethyl amide 1a–c and morpholide amide 2a–c) in the cone conformation were carried out. Binding was assessed by extraction experiments of the metal picrates from water to dichloromethane and proton NMR titrations. Density functional theory calculations were also performed to determine the binding energy of the complexes formed and to analyse the host–guest interaction modes. In the cases of ligands 1b and 2c with Na⁺ and Ag⁺ picrates, the extraction energy was also determined using the polarisable continuum model. The results are discussed in terms of the nature of the amide residue and the substitution pattern (1,3 vs. 1,2). Both tetra-amide derivatives are good extractants, showing preference for Na⁺, Ca²⁺, Ag⁺ and Pb²⁺ cations, mainly di-ethylamide 1a. Concerning di-amide derivatives, the relative position of the substituents seems to be more important than the nature of the amide group in the extraction process. Proton NMR studies indicate the formation of 1:1 complexes between the amides and the cations studied, and DFT data show that all ligands form the most stable complexes with La³⁺.     

Efficient divalent metal cation extractions with di-ionizable calix[4]arene-1,2-crown-4 compounds

Di-ionizable calix[4]arene-1,2-crown-4 ethers in the cone conformation were synthesized and their conformation and regioselectivity verified by NMR spectroscopy. These new ligands exhibited high Ba²⁺ selectivity in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform. The selectivity order was Ba²⁺>>Sr²⁺>Ca²⁺>Mg²⁺ with Ba²⁺/Sr²⁺ selectivity exceeding 100. The ligands also exhibited high extraction ability for Pb²⁺ and for Hg²⁺ in single species extraction. With variation of proton-ionizable groups, which are oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, ‘tunable’ ligand acidity was obtained.     

A Thermodynamic Study Between 18-Crown-6 with Mg2+, Ca2+, Sr2+and Ba2+ Cations in Water–Methanol and Water–Ethanol Binary Mixtures Using The Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca²⁺ and Sr²⁺ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K _f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺. The values of thermodynamic parameters (Δ H _c ° and Δ S _c °) for formation of 18C6–Mg²⁺, 18C6–Ca²⁺, 18C6–Sr²⁺ and 18C6–Ba²⁺complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H _c ° and Δ S _c °) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number.     

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands: synthesis and high divalent metal ion extraction selectivity

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ethers in the cone conformation are synthesized with their conformation and regioselectivity verified by NMR spectroscopy. The new ligands are efficient extractants with high selectivity for Ba²⁺ in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform.     

Synthesis and complexing properties of four imidazolyl acetamido p-tert-butylcalix[4]arenes

Four imidazolyl acetamido p-tert-butylcalix[4]arenes 5–8 have been prepared by reacting the corresponding methyl esters derivatives 1–4 with histamine in 1:1 mixture of methanol:toluene. The yields ranged from 56 to 68%. 5–8 have been shown to be in cone conformation. The complexation behaviour of 5–8 towards monovalent metal picrates M⁺Pic⁻ with M⁺ = Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ and divalent metal picrates M²⁺(Pic⁻)₂ with M²⁺ = Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Zn²⁺ and Co²⁺ are given. Tentative localisation of the metal cations in the receptors is given. The binding properties towards these cations have been determined along with stoichiometries of the complexes.     

Tetra(diethyl)amide-p-tert-butyl-thiacalix[4]arene in Cone Conformation: Synthesis and Binding Properties with Alkali,Alkaline Earth,Heavy and Transition Metal Ions

Tetra(diethyl)amide-p-tert-butylthiacalix[4]arene 1a in the cone conformation was synthesized and its binding properties towards a large variety of metal ions were established on the basis of liquid–liquid and solid–liquid extraction as well as complexation experiments. This compound is a less efficient and selective compound than the “classical” tetra(diethyl)amide-p-tert-butylcalix[4]arene 3 in the cone conformation for alkali and alkaline earth metal ions. However, Pb²⁺ is selectively extracted and complexed within heavy and transition metal ions.     

Synthesis,Conformational Analysis and Extraction Studies of p-isopropylcalix[n]arene Derivatives (n = 4, 6, 8). A New Family of Molecular Receptors

Abstract

Ethers, esters and ketones, derivatives of p-isopropylcalix[n]arenes (n = 4,6,8), have been prepared; 33 new molecular receptors have been isolated and fully characterized. ¹H NMR and ¹³C NMR measurements reveal that tetraester and tetraketone derivatives are in cone conformation at room temperature when hexa and octa derivatives look like flexible flattened cones. Extraction studies with metal picrates from aqueous solution into dichloromethane were used to assess the ionophoric activity of the p- isopropylcalix[n]arene derivatives. The better E% are obtained with tetrameric derivatives in cone conformation, fully functionalized on the phenolic oxygens by ester or ketonic groups. The tetraamide derivative is the most efficient binder; the E% values are around 100 for Li, Na, K, Rb, Cs, Ca and Ba.     

Study of Complex Formation Between Dicyclohexano-18-Crown-6 (DCH18C6) with Mg 2+, Ca2+, Sr 2+, and Ba2+ Cations in Methanol–Water Binary Mixtures Using Conductometric Method

The complexation reactions between Mg²⁺,Ca²⁺,Sr²⁺ and Ba²⁺ metal cations with macrocyclic ligand, dicyclohexano-18-crown-6 (DCH18C6) were studied in methanol (MeOH)–water (H₂O) binary mixtures at different temperatures using conductometric method . In all cases, DCH18C6 forms 1:1 complexes with these metal cations. The values of stability constants of complexes which were obtained from conductometric data show that the stability of complexes is affected by the nature and composition of the mixed solvents. While the variation of stability constants of DCH18C6-Sr ²⁺ and DCH18C6-Ba²⁺versus the composition of MeOH–H₂O mixed solvents is monotonic, an anomalous behavior was observed for variations of stability constants of DCH18C6-Mg²⁺ and DCH18C6-Ca²⁺ versus the composition of the mixed solvents. The values of thermodynamic parameters (ΔH_c°, ΔS_c°) for complexation reactions were obtained from temperature dependence of formation constants of complexes using the van’t Hoff plots. The results show that in most cases, the complexation reactions are enthalpy stabilized but entropy destabilized and the values of thermodynamic parameters are influenced by the nature and composition of the mixed solvents. The obtained results show that the order of selectivity of DCH18C6 ligand for metal cations in different concentrations of methanol in MeOH–H₂O binary system is: Ba²⁺>Sr²⁺>Ca²⁺> Mg²⁺.     

Calix[4]Arenes in the partial cone conformation as ionophores in silver ion-selective electrodes

Two calix[4]arene derivatives, in the partial cone conformation, with sulfur-containing functionalities, were tested as neutral carrier ionophores in potentiometric silver-selective electrodes of conventional membrane and membrane-coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2-nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p-chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec⁻¹) in the range 10⁻⁴–10⁻¹ M and excellent selectivity [log K_Ag,_MH+ < −1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in the cone conformation.     

Extraktion von Alkali- und Erdalkalimetallpikraten aus wässerigen Lösungen in Methylenchlorid durch ungeladene azyklische Ionophoren. Quantitative Interpretation

Extraction of alkali and alkaline earth metal picrates from water into methylene chloride. Quantitative interpretation The ligands N, N, N′, N′-tetraphenyl-3, 6-dioxaoctanediamide (1) , (?)-(R, R)-N, N′di [(ll - ethoxycarbonyl) undecyl] - N, N′, 4, 5-tetramethyl-3, 6-dioxaoctanediamide (2) , and N, N′-diheptyl-N, N′, 5,5-tetramethyl-3,7-dioxanonanediamide (3) , reported earlier as components for liquid membrane electodes with selectivity for Ba²⁺ (1) , Ca²⁺ (2) and Li⁺ (3) , were used to study models for the extraction of alkali and alkaline earth metal picrates from water into methylene chloride. The composition of the extracted complexes of alkaline earth cations with 1 and 2 proved to be mono- and diassociated with the picrate anion. The extraction selectivity observed for 1, 2 , and 3 towards different cations paralleled the potentiometric selectivity factors obtained for liquid membrane electrodes with 1, 2 , and 3 as membrane components.     

The Preorganization Effect of the Calix[4]arene Platform on the Extraction Properties of Acetylhydrazide Groups with Transition Metal Ions

The binding properties of the cone conformer of O,O,O,O-tetrakis[hydrazinocarbonylmethyl]-4-tert-butylcalix[4]arene, the cone and the 1,3-alternate conformers of the corresponding thia analogue have been evaluated by means of liquid–liquid extraction for a large variety of metal ions. The extraction constants and the stoichiometries of the complexes formed have been determined. Comparison of the extraction properties of calix[4]arenes with their acyclic monomeric analogue clearly demonstrated, that the preorganization of acetylhydrazide groups on the calix[4]arene platform is the cause for a significant improvement of its binding properties. The presence of additional “soft” nitrogen binding sites in acetylhydrazide derivatives of calix[4]arenes compared to their amide derivatives leads to a shift from their classical selectivity for alkali and alkaline earth cations to transition metals. The cone conformer of tetrathiacalix[4]arene shows higher selectivity in a series of d-metal ions compared with its “classical” analogue. The 1,3-alternate conformer exhibits an excellent extraction selectivity for Cu²⁺ and Hg²⁺.     

Sulphur-enriched thiacalix[4]arenes in the cone conformation: synthesis, crystal structures and cation binding properties

The synthesis and crystal structure of p-tert-butylthia- and p-tert-butylcalix[4]arene derivatives 1–7 substituted at the narrow rim by diethylthiophosphate ester groups, -PS(OEt)₂ are reported. In these compounds the phosphorus atoms are directly attached to the phenolic O atoms of the calix units and the S atoms of the thiophosphate may serve as a two-electron donor to a metal ion. Their crystal structures were solved, which revealed their cone conformation. Their cation-binding properties have been established by liquid-liquid extraction of metal picrates from water into dichloromethane and stability constant determination in acetonitrile using UV-absorption spectrophotometry. Quantitative extraction was achieved for Ag⁺ (%E = 99) with the tetra-substituted thiacalix[4]arene derivative. The complexes were found to be of 1:1 stoichiometry and the location of the metal cations was shown to be nearby the sulphur atoms by ¹H NMR.     

Transition Metal Ion-binding Properties of a 14-Membered N2O2S2- Macrobicyclic Ligand

The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N₂O₂S₂-macrobicycle. Metal picrates such as Pb²⁺, Co²⁺, Zn²⁺, Ni²⁺,Cu²⁺ and Cd²⁺ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb²⁺ only among the other metals. The extraction constant (log K _ex) was determined to be 13.8 for Pb²⁺ complex.     

Synthesis, 1H-NMR conformational analysis and complexation studies of two di-imidazolyl acetamido p-tert-butylcalix[4]arenes

The synthesis of a new di-imidazolyl-di-methoxy acetamido p-tert-butylcalix[4]arene 4 is reported. 4 has been prepared by reacting the corresponding di-methyl ester di-methoxy derivative with histamine in 1:1 mixture of methanol: toluene. The binding properties of 4 towards alkali, alkaline earth, transition (Zn²⁺, Co²⁺) and heavy (Pb²⁺, Cd²⁺) metals have been investigated along with the complexes stoichiometries. The ¹H-NMR spectra of complexes show the location of cations in receptor 4. Partial cone conformation is observed only with strontium and calcium whereas the cone conformation is detected with most of the cations. Comparison of the complexation results with those obtained for di-imidazolyl acetamido p-tert-butylcalix[4]arene 3 missing the methyl groups is also reported.