Search

The intrinsic electronic absorption and fluorescence properties of several multifluorophoric dihomooxacalix[4]arenes are studied. The contributions of phenyl and/or benzyl groups (lower rim) and p-tert-butylphenyl ethers (upper rim) to the absorption and fluorescence are established. Fluorescence titrations were undertaken to investigate the calixarene complexes with nitrate and hydrogen sulfate. A comparison with UV-Vis titrations in the same concentration range showed that similar values for the association constants are obtained by both techniques. Fluorescence is thus demonstrated to be a good method for the determination of calixarene–anion association constants.

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2-pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p-tert-butylhexahomotrioxacalix[3]arene (1a) was assessed by spectrophotometry, microcalorimetry, proton NMR spectrometry and density functional theory methods.

Heteracalixarenes are members of the calixarene family in which heteroatoms such as oxygen, nitrogen, sulfur, selenium, or silicon are inserted between the methylene bridges or replace them entirely. The incorporation of heteroatoms affects the metal binding affinities of these calixarenes over their all-carbon analogues, through the abilities of the heteroatoms both to bind directly and to influence lower rim phenolic binding. This chapter covers the literature concerning phenolic homooxa- and homoazacalixarene-metal complexes mainly for the last two decades (1994–2014). The syntheses of homooxa- and homoazacalixarenes containing free OH groups at the lower rim are described and their coordination chemistry towards alkali, alkaline earth, transition, heavy, lanthanide and actinide metals is discussed. Examples of crystal structures of these metal complexes are given, as well as brief descriptions of their applications in fields such as catalysis, and metal cation extraction and transport. Keywords: alkali and alkaline earth metals; coordination chemistry; homoazacalixarenes; homooxacalixarenes; lanthanide and actinide metals; metal phenolates; metal complexes; transition and heavy metals

The binding properties of two homooxacalixarene diethylamides (1b and 2b) derived from p-tert-butyldihomooxacalix[4]arene and p-tert-butylhexahomotrioxacalix[3]arene, respectively, in the cone conformation, for lanthanide cations, were investigated. These properties were assessed by extraction studies of the metal picrates from water into dichloromethane and stability constant measurements in methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of La3+, Pr3+, Eu3+ and Gd3+ complexes in the same solvent were also performed. Proton NMR titrations with the representative lanthanides La3+, Eu3+ and Yb3+ were also carried out to establish the sites of interaction of the ligands with the cations. The analogous derivative (3b) of p-tert-butylcalix[4]arene was also studied and the results of the three compounds are compared. Diethylamide 1b is the strongest binder, showing some preference for the light lanthanides in extraction, but exhibiting practically no selectivity in c...

p-tert-Butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone (1b) was synthesized for the first time. Compound 1b was obtained in a cone conformation in solution at room temperature, as established by NMR spectroscopy (H-1 and C-13). The binding properties of ligand 1b for alkali, alkaline earth, transition, heavy metal and lanthanide cations have been assessed by phase transfer and proton NMR titration experiments. Molecular mechanics and ab initio techniques were also employed to complement the NMR data. The results are compared to those obtained with other closely related homooxacalixarene derivatives. Although triketone 1b is a weak extractant, it shows a strong peak selectivity for Na+ and also some preference for Ag+. Proton NMR titrations indicate the formation of 1:1 complexes between 1b and the cations Studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Although the molecular mechanics results show little correlation with the NMR data, a good agreement was obtained with the ab initio models. (C) 2008 Elsevier Ltd. All rights reserved.

1,3-Dimethoxy- p - tert -butyldihomooxacalix[4]arene-crown-6 ( 4 ) was synthesized for the first time. 4 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements ( 1 H, 13 C, COSY and NOESY). Conformational behaviour of 4 and p - tert -butyldihomooxacalix[4]-crown-5 ( 2 ) and crown-6 ( 3 ) was studied by dynamic 1 H NMR and by MD/MM calculations. Two-phase (water/CH 2 Cl 2 ) picrate extraction studies and transport experiments with the same salts through a CH 2 Cl 2 membrane were performed to evaluate the binding properties of these ligands towards alkali and alkaline earth metal cations. 2 and 3 are poor phase transfer agents for all cations, while 4 is a reasonable extractant for the alkali cations, showing preference for Cs + . However, all three calixcrowns are good carriers for the alkali cations and display a very selective transport for Ba 2+ .

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 μmol h-1) found until now with dihomooxacalix[4]arene derivatives.

The tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene (2) was synthesized for the first time. This derivative possesses the cone conformation in solution at room temperature, which was confirmed by NMR measurements (1H, 13C and NOE 1D). Extraction studies with metal picrates from neutral aqueous solution into dichloromethane, transport experiments with metal picrates through a dichloromethane membrane and stability constant measurements by UV absorption spectroscopy in methanol and acetonitrile were performed to evaluate the binding ability of ketone 2 towards alkali and alkaline earth metal cations. The tetraphenylketone of p-tert-butylcalix[4]arene (3) was also studied, and the results for the two derivatives were compared. Compound 2 shows a preference for K+ and Ba2+ cations, being selective only in the alkaline earth metal cation series. Compound 3 is a stronger binder than 2, but is a weaker extractant. Both show transport rates that are not proportional to complex stability or to extraction efficiency. Ketone 2 can be characterized as a selective receptor. Copyright © 1999 John Wiley & Sons, Ltd.

The diethyl amides of p-tert-butyldihomooxacalix[4]arene (1), p-tert-butylhexahomotrioxacalix[3]arene (2) and p-tert-butylcalix[4]arene (3) were used as active materials in ion-selective membrane electrodes to check the detection of different kinds of cations (Na+, K+, Cs+, Mg2 + , Ca2 + , Mn2 + , Cu2 + , Zn2 + , Cd2 + , Pb2 + and tetramethylammonium cation). The electrode characteristics and selectivity coefficients were determined and compared. Optimisation of the PVC membrane composition was achieved using three different plasticisers (bis(2-ethylhexyl) adipate, o-nitrophenyl octyl ether and bis(2-butylpentyl) adipate). Amide 3 shows selectivity for Na+, whereas compounds 1 and 2 exhibit the highest selectivity for Pb2 + among all the studied cations. The X-ray crystal structure of dihomooxacalix[4]arene tetra(diethyl)amide (1) was determined, revealing it to be in the cone conformation.

1,3-Diethoxy-p-tert-butyldihomooxacalix[4]arene-crown-6 (3) was synthesised for the first time. Compound 3 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements (1H, 13C and NOESY). The assignment of both proton and carbon NMR spectra was achieved by a combination of COSY and HSQCTOCSY experiments. The binding affinities of ligand 3 for alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. Compound 3 is a reasonable extractant for the alkali cations and also for Ag+, showing preference for Cs+. Ligand 3 forms 1:1 complexes with K+, Ca2+, Ag+ and Pb2+, as determined by proton NMR titrations, which also indicated that these cations should be encapsulated into the cavity defined by the crown ether unit, the ethoxy group and the inverted aryl ring. A new dihomooxacalix[4]crown-6 (3) was synthesised and isolated in a partial cone A conformation in solution at room temperature, as established by NMR (1H, 13C and NOESY). The binding properties of 3 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with calixcrowns 1 and 2.[image omitted].

The binding of alkali, alkaline earth, transition (Mn2 + , Fe2 + , Co2 + , Ni2 + , Cu2 + and Zn2 + ) and heavy metal (Ag+, Cd2 + , Hg2 + and Pb2 + ) cations by cone p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide (1b) has been assessed by extraction studies of metal picrates from water to dichloromethane and proton NMR titration experiments. Molecular modelling techniques were also employed to complement the NMR data. The results are compared to those obtained with the dihomooxacalix[4]arene (2b) and calix[4]arene (3b) derivative analogues. Triamide 1b displays a high extracting ability towards Na+, Ba2 + , Ni2 + , Co2 + , Ag+ and mainly Pb2 + (80% E). However, these values are lower than those obtained with tetraamides 2b and 3b, presumably due to the higher conformational flexibility of 1b. 1H NMR titrations indicate the formation of 1:1 complexes between 1b and all the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms.

The binding properties of three p-tert-butyldihomooxacalix[4]arene tetraketone derivatives (tert-butyl 2b, adamantyl 2c and phenyl 2d) in the cone conformation and one derivative (methyl 2a) in a partial cone conformation, towards alkali and alkaline earth metal cations have been established by extraction studies of metal picrates from water into dichloromethane, stability constant measurements in methanol and acetonitrile, and by H-1 NMR spectrometry. Transport experiments of metal picrates through a dichloromethane membrane were also performed. The results are compared to those obtained with closely-related calix[n]arene derivatives (n = 4 and 5) and discussed in terms of the substituents, size and conformational effects. Methylketone 2a is a poor binder for all the cations studied, due to its partial cone conformation. Ketones 2b, 2c and 2d show high extraction and complexation levels for the alkali cations, with similar profiles and preference for K+ and Na+ (plateau selectivity). Towards alkaline earth cations, these ketones show a strong peak selectivity for Ba2+ in extraction, but a plateau selectivity for Ca2+, Sr2+ and Ba2+ in complexation. The nature of the substituent attached to the ketone function has some influence on their binding properties, with phenylketone 2d being a slightly weaker binder than ketones 2b and 2c. H-1 NMR titrations confirm the formation of 1:1 complexes between the ketones and the cations studied, also indicating that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Ketones 2b, 2c and 2d show transport rates that do not follow, in general, the same trends observed in extraction and complexation.

1,3-Di(2-pyridymethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (H-1, C-13 and NOESY). Complete assignment of both proton and carbon NMR spectra wits achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crowns-6 derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd2+), with it very strong affinity for Ag+. Some transition metal cations are also well extracted. 2 Forms 1: 1 complexes with K+, C2+ and Ag+, and H-1 NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML2) complex is formed with Zn2+ and two species, probably 1: 1 and 1:2 complexes, are obtained with Ph (c) 2006 Elsevier Ltd. All rights reserved.

The binding properties of the tetra( diethyl) amide ( 2) derived from p-tert-butyldihomooxacalix[4]arene, in the cone conformation, towards alkali, alkaline earth, transition (Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and heavy (Ag+, Cd2+, Hg2+ and Pb2+) metal cations have been established by extraction studies of metal picrates from an aqueous solution into dichloromethane, transport experiments with the same salts through a dichloromethane membrane and stability constant measurements in methanol. Results concerning the calorimetric study of Na+ and K+ complexes in methanol are presented. The affinity of 2 for some cations (Na+, K+, Ba2+, Ag+ and Zn2+) has been investigated by H-1 NMR spectrometry, as well. The results are compared to those obtained with the analogous calix[4]arene tetraamide derivative 3. Amide 2 displays a preference for the alkali cations (mainly Na+ and K+) in contrast to amide 3 that prefers the alkaline earth cations. Ag+ and Cd2+ soft Lewis acids are also strongly bound by both amides. H-1 NMR titrations confirm the formation of 1: 1 complexes between 2 and all cations studied, also suggesting that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. 2 shows transport rates that do not follow the same trends as the stability constants or extraction percentages; it can therefore be characterized as a selective receptor.

The binding properties of three p-tert-butyldihomooxacalix[4]arene tetraketone derivatives ( tertbutyl 2b, adamantyl 2c and phenyl 2d) in the cone conformation and one derivative ( methyl 2a) in a partial cone conformation, towards transition ( Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and heavy (Ag+, Cd2+, Hg2+ and Pb2+) metal cations have been established by extraction studies of metal picrates from water into dichloromethane, transport experiments with the same salts through a dichloromethane membrane and stability constant measurements in methanol and acetonitrile. Results concerning the microcalorimetric study of Cu2+, Ag+ and Pb2+ complexes in methanol are presented. The affinity of the ligands for some cations ( Zn2+, Ag+, Pb2+ and Hg2+) has also been investigated by proton NMR spectrometry. The X-ray crystal structure of tert-butylketone 2b was determined. Towards transition metal cations, ketones 2b, 2c and 2d are reasonable binders, showing in general preference for Cu2+. Methylketone 2a is a poor binder for these cations, due to its partial cone conformation. The three ligands in the cone conformation present a high affinity for the heavy metal cations, with selectivities for Ag+ and Pb2+. This series of cations is even fairly well complexed by methylketone 2a, which presents high stability constants for Hg2+ and Pb2+. The cases studied by H-1 NMR titrations confirm the formation of 1 : 1 complexes between the ketones and the cations, also indicating that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Ketones 2b, 2c and 2d show transport rate sequences that follow, in general, the same trends observed in extraction and complexation for transition cations, but they are reversed for the heavy metal cations.

The binding properties of tetra(2-pyridylmethoxy) (2) derived from p-tert-butyldihomooxacalix[4]arene, in the cone conformation, towards alkali, alkaline earth, transition (Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and heavy (Ag+, Cd2+, Hg2+ and Pb2+) metal cations have been assessed by extraction studies of metal picrates from water into dichloromethane and stability constant measurements in methanol and acetonitrile. Results concerning the calorimetric study of K+, Ba2+, Cu2+ and Ag+ complexes in acetonitrile are presented. The affinity of 2 for some cations (K+, Ag+, Zn2+, Hg2+ and Pb2+) has also been investigated by proton NMR spectrometry. The analogous derivative (3) of p-tert-butylcalix[ 4] arene was also studied, and the results of both compounds are compared. Towards the hard alkali and alkaline earth metal cations ligands 2 and 3 display a low efficiency of extraction. The complexation levels are also low in methanol becoming, however, much higher in acetonitrile. The highest stability is found for Ca2+ with ligand 2 in this solvent. Both ligands show a very high affinity for the soft heavy metal ions with preference for Ag+, but other ions such as Hg2+, Pb2+ and Cu2+ are also well bound. Proton NMR titrations confirm the formation of 1 : 1 complexes between 2 and all the cations studied, also indicating that they should be located inside the cavity defined by the phenoxy oxygen and the pyridyl nitrogen atoms.

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 ≥ ...

The metal cation binding ability of cone-p-tert-butylhexahomotrioxacalix[3]arene tris(acetic acid) was investigated by 1H NMR and complementary semi-empirical calculations. NMR showed significant shifts with Na+, K+, Ag+ and, to a lesser extent, Pb2+. The macrocyclic protons undergoing the greatest shifts imply that these cations bind inside the cavity composed of the phenoxy and carbonyl oxygen atoms. Metal complexes were modelled using a semi-empirical approach and, in general, their geometry optimised structures were in agreement with NMR data. U-tube transport experiments demonstrated that the macrocycle actively transported Cr3+, Fe3+, Co2+ and Cu2+ through the organic phase.