Crown-containing butadienyl dyes 8. Structures and complexation of chromogenic dithia-15(18)-crown-5(6) ethers

The structures of new butadienyl dyes of the benzothiazole series containing the dithia-15-crown-5 (2a) or dithia-18-crown-6 (2b) fragments were established by X-ray diffraction. Complexation of dyes 2a,b with Hg²⁺, Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, and alkaline-earth cations in aqueous-acetonitrile solutions was studied by spectrophotometry. At a high percentage of water in solutions (P _w ≈ 50%), these dyes have a very low ability to bind Pb²⁺ cations (logK < 2) and virtually do not bind Cd²⁺, Zn²⁺, and alkaline-earth cations. At the same time, these dyes form stable 1: 1 complexes with Hg²⁺ and Ag⁺ cations at all P _w. The stability constants of complexes with the Ag⁺ cation increase with increasing P _w because the free energy of hydration of this cation is much lower than the free energy of solvation in acetonitrile. In the P _w range from 0 to 75%, the stability constants of the complexes of dyes 2a,b with the Hg²⁺ cation are larger than those of the corresponding complexes with the Ag⁺ cation by more than four orders of magnitude. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 90–96, January, 2006.     

Crown ether styryl dyes

New crown ether-containing styryl dyes of the benzothiazole series containing an aza-15-crown-5-ether moiety were synthesized. Thetrans-cis-photoisomerization of these dyes and their analogs was studied; the effect of metal cations on the kinetics of darkcis-trans-isomerization was elucidated. The stability constants of the complexes of thecis-isomers of these dyes with Ca(ClO₄)₂ were estimated. The dramatic increase (by more than three orders of magnitude) in the stability of the complexes on passing from a cationic dye to a betaine was attributed to the formation of an intramolecular bond in thecis-complexes between the sulfo group of theN-substituent and the metal cation located in the cavity of the azacrown-ether moiety.     

Synthesis,complexation, and <Emphasis Type="Italic">E—Z</Emphasis> photoisomerization of azadithiacrown-containing styryl dyes as new optical sensors for mercury cations

New styryl dyes containing azadithia-15-crown-5 fragments were synthesized. The complexation of these compounds with Ag⁺, Pb²⁺, Cu²⁺, Hg²⁺, and H⁺ cations was studied by ¹H NMR spectroscopy, steady-state, and time-resolved spectroscopy. The stability constants of the complexes were calculated from the spectrophotometric titration data. The photophysical properties and E—Z photoisomerization of styryl dyes and their complexes with mercury and copper(II) cations in acetonitrile were examined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 495–507, March, 2007. Centre de Physique Moléculaire Optique et Hertzienne-UMR CNRS 5798, Bordeaux University I, 351 Cours de la Libération, 33405 Talence, France.     

Stability constants of complexes formed by new Schiff-base lariat ethers derived from 4,13-diaza-18-crown-6 with Ag+, Pb2+, Cu2+ cations determined by competitive potentiometry

The stability of complexes formed by a series of Schiff-base lariat ethers, derived from 4,13-diaza-18-crown-6, 1 with Ag⁺, Pb²⁺, Cu²⁺ cations, has been comparatively determined, in methanol: dichloromethane solution. We present here the synthesis and an interesting competitive potentiometry method useful for the stability constant determination for a new family of Schiff-base bibracchial lariat ethers. The stability constants and the selectivity in competitive complexation of Ag⁺, Pb²⁺ and Cu²⁺ cations by macrocyclic receptors 1–7 (L), can be accurately evaluated and species distribution diagrams can be calculated for individual system. In all cases further functionalization of bibracchial lariat ethers 2–7 is accompanied by an increasing of the selectivity, relative to the complexes of the initial 4,13-diaza-18-crown-6 macrocycle 1.     

COMPLEX FORMATION BETWEEN HEAVY METAL CATIONS AND DIAZA CROWN ETHERS AND CRYPTANDS IN AQUEOUS SOLUTION

Abstract

Complexation of some heavy metal cations in aqueous solution by diaza crown ethers and cryptands has been studied using pH-metric titrations. In most cases, macrobicyclic cryptands form more stable complexes than diaza crown ethers. The size of the cavity aiso influences the stability of the complexes formed.     

Crown-ether styryl dyes

Styryl dyes (4a,b) containing a 15-crown-5 fragment and isomeric 2- and 4-quinolinium residues with anN-sulfopropyl substituent undergo [2+2]-autophotocycloaddition to give cyclobutane derivatives (9a,b) in acetonitrile only in the presence of Mg(ClO₄)₂ or Ca(ClO₄)₂. The stereospecificity of both pathways of photocycloaddition and its efficiency are explained by the preorganization of the supramolecular dimers derived from thetrans-isomers of the dyes when they are bound into complexes with Mg and Ca cations.For Part 14, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2225–2230, November, 1995.The work was carried out with financial support from the Russian Foundation for Basic Research (Project code 94-03-08531) and the International Science Foundation (Grants ISF, M8Q000 and N38000).     

Crown Ether Complexes of Six-Membered N-heteroaromatic Cations

Crown ether complexes of six-membered N-heteroaromatic cations and the closely related bicyclic purinium cation (6) have been studied by ¹H NMR, mass spectrometric and crystallographic methods. The stability constants for the complexes were determined by ¹H NMR titration in acetonitrile solution and the complexation stoichiometry by ¹H NMR and ESI mass spectrometric methods. Altogether six crystal structures of complexes were determined to study the complexation in the solid state. Hydrogen bonding was observed to be the most important interaction for the complexation both in solution and in the solid state but – interactions also contribute to it. All crystal structures of the DB18C6 complexes with six-membered N-heteroaromatic cations, except for 4-hydroxypyridinium, are isomorphous to previously studied five-membered N-heteroaromatic cations and pyridinium complexes. Such a close resemblance is not observed in B18C6 and 18C6 complexes or DB18C6purinium (6).     

COMPLEXATION OF ALKALINE EARTH CATIONS BY NONCYCLIC POLYETHERS,CROWN ETHERS,AND CRYPTANDS IN ACETONE

Abstract

The complexation of akaline earth cations by non-cyclic polyethers, crown ethers and cryptands was studied in acetone by means of potentiometric and calorimetric titrations. The results show that the stabilities of the complexes decrease in the order: cryptands, crown ethers and noncyclic polyethers. Interactions between the different ligands and solvent molecules influence the stability of the complexes formed when compared with methanol as solvent.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.     

Various aspects of enantiomeric recognition of (S,S)-dimethylpyridino-18-crown-6 by several organic ammonium salts

Abstract

Factors responsible for complex stability and enantiomeric recognition for the interactions of (S,S)-dimethylpyridino-18-crown-6 with several organic ammonium salts were examined using an ¹H NMR technique. The results indicate that cation structures have a significant effect on enantiomeric recognition; solvents play a very important role in the stability of the complexes, and anions can compete with ligands for the ammonium cations.     

Thiocarbamide derivatives of europium,holmium, and erbium iodides: Synthesis and structures

Data on the synthesis, IR spectra, and X-ray diffraction analysis of the thiocarbamide complexes of europium, holmium, and erbium iodides, [Ln(H₂O)₉]I₃ · 2CS(NH₂)₂ (Ln = Eu (I), Ho(II), Er (III)), are presented. The crystal structures of the complexes contain nonaaqualanthanide cations (the polyhedron shape is a monocapped tetragonal antiprism), outer-sphere thiocarbamide molecules, and uncoordinated iodide ions. The thiocarbamide molecules form hydrogen bonds with the aqua cations and join them into continuous layers or network ensembles. The thiocarbamide molecules are disordered in the crystal structures of complexes II and III.     

Crown-containing butadienyl dyes

Crown-containing butadienyl dyes containing various heterocyclic moieties and azacrown ether fragments were synthesized for the first time. The spatial structures and the absorption and fluorescence spectra of crown-containing butadienyl dyes and their complexes with metal cations were examined. The effects of the nature of the heterocyclic and crown ether fragments on fluorescence and generation of dyes and their complexes with metal cations were revealed based on the spectral data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 530–541, March, 1999.     

THE INFLUENCE OF STRUCTURAL EFFECTS ON THE COMPLEXING ABILITY OF CROWN ETHERS

Abstract

Simple regression including interaction energies of the cation-ligand systems explains to some extent the variability in logarithms of stability constants of complexes formed by a series of nine 18-crown-6 ethers with potassium cations in methanol. The atomic charges were calculated for energy minimized structures, found during molecular dynamics computations. In order to mimic the residual solvation of complexed cations, two CH₃OH molecules were incorporated above and below the macrocyclic plane. Polarization effects of the metal cation on the resulting atomic charges were considered in calculations and found to be crucial for satisfactory correlations with experimental data.     

Complexation of crown-containing butadienyl dyes with alkali and alkaline earth metal cations in the ground and excited electron states

Spectrophotometry and steady-state fluorimetry were used for the study of complexation of crown-containing butadienyl dyes with alkali and alkaline earth metal cations in acetonitrile, as well as protonation of these dyes with trifluoroacetic acid. Complexation of the compounds studied with the metal cations leads to the 1: 1 product, whereas protonation with trifluoroacetic acid affords the 1: 2 product containing 2 moles of the acid per 1 mole of the dye. Stability constants of the complexes are varied from 10 to 10⁶ L mol⁻¹, basicity of the crown-containing dyes in the reaction with trifluoroacetic acid increases with the increase in the macrocycle size. On complexation, the fluorescence spectra are shifted considerably less than the absorption spectra. This indicates that photorecoordination of the cation in the complex excited molecules occurred. Based on the correlation of the spectral shifts with the metal cation charge density, three types of complexes differing in the extent of influence of the cation charge on the spectral shifts can be singled out: “tight”, “loose”, and “solvent-separated”.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.Graphical Abstract Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali CationsYU LIU*, JIAN-RONG HAN, ZHONG-YU DUAN and HENG-YI ZHANG This revised version was published online in July 2005 with a corrected issue number.     

Catalytic activity of Mn(III) and Co(III) complexes: evaluation of catechol oxidase enzymatic and photodegradation properties

We have synthesized two mononuclear complexes, Mn-hq and Co-hq, to serve as sustainable catalysts (for degrading dyes from organic pollutant) and as biocatalysts (for promoting oxidation of catechol to quinone). The two complexes have been characterized by various spectroscopic tools, and with the assistance of single-crystal X-ray diffraction data, their molecular structures were established. The present complexes were exploited for the catalytic activity, i.e., enzymatic activity and photocatalytic property. In methanolic solution, Mn-hq and Co-hq were examined for catecholase-like activity and Mn-hq particularly catalyzes the oxidation of 3,5-di-tert-butyl catechol to analogous quinone with a K_cat value of 835.2 h^?1. Additionally, Mn-hq and Co-hq demonstrated remarkable photocatalytic activity for the degradation of methylene blue (MB) in the aqueous medium beneath visible light. Co-hq shows excellent stability and recyclability toward MB. Further, trapping experiment along with degradation pathways is also explored. Thus, the present research throws light on the excellent catalytic properties of simply designed complexes and this activity can be tuned for desired efficiencies in future prospects.

     

A Thermodynamic Study Of N,N,N',N'-Tetrakis(2-Hydroxyethyl)-Ethylenediamine Complexes With Nickel(II), Copper(II), And Zinc (II)

Abstract

Thermodynamic parameters have been determined by poten-tiometric techniques for complex ions formed by N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine TKED, with nickel (II), copper(II), and zinc(II) ions. The formation constants, enthalpy, and free energy data for the complexes exhibited values qualitatively consistent with predicted ligand field stabilization trends for these cations. The general expected stability of the complexes in the order Ni(II) < Cu(II) > Zn(II) is observed.     

A Study of Formation Equilibria of the Complexes of Some Metal Cations with Polyoxa Macrocyclic Ligands

Abstract

The complexes formed by the Na⁺, K⁺, Rb⁺, Ca²⁺, UO²⁺ ₂, and Ag⁺ cations with the macrocyclic polyethers 18-crown-6, benzo-15-crown-5, and dicyclohexy1-18-crown-6 are investigated. The stability constants of these complexes have been determined potentiometrically in (90% vol.) ethanol-water solutions at 25[ddot]C and an ionic strength μ= 0.1 (achieved with tetrabuty lammonium perchlorate). The stablity of the investigated complexes was interpreted in terms of “caging” the metal cation into the cavity of the macrocyclic ligand, an effect which depends on the ratio of the diameter of the complexed cation over the diameter of the cavity of the complexing ligand.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study

The absorption spectra of styrylbenzothiazolium dye derivatives were calculated by the time-dependent density functional (TD DFT) method. The dyes of interest were (p-dimethylamino)styrylbenzothiazolium dye and its protonated form as well as aza-15(18)-crown-5(6)-containing dyes and their complexes with alkali (K⁺ and Na⁺) and alkaline-earth (Ca²⁺, Sr²⁺, and Ba²⁺) cations. Several low-lying conformers of the azacrown-containing dyes were considered. The electronic and geometric structures of the excited states responsible for the appearance of the long-wave (π-π*) absorption bands are studied. Complexation causes a hypsochromic shift of the long-wave absorption band correlating with the pyramidality of the crown ether nitrogen in the complex. The interaction of the cation with 3–4 solvent molecules or a counterion (ClO₄ ^?) considerably reduces this shift, especially in the conformers without the metal-nitrogen bond. In some cases, the long-wave absorption band is close to the absorption band of the free dye. Similar results were obtained using the polarizable continuum model of solvation. Excited-state structures of the free model dye and the free azacrown-containing dyes exhibit a tendency to bond alternation. Conversely, the cationic complexes of the crown-containing dyes and the protonated model dye exhibit a tendency to bond equalization in the excited state. The changes in the excited-state geometries of the free dyes and their complexes account for the complexation-induced fluorescence enhancement observed in the experiments.     

Crown-ether styryl dyes

The surface enhanced Raman scattering (SERS) spectra of styryl dyes containing a crown-ether group and a heteroaromatic residue with sulfoalkyl (1a) or alkyl (1b)N-substituent and of their complexes with Mg²⁺ cations were recorded in the 10^–4–10^–8 mol L^–1 concentration range. A model for the interaction of compoundsla,b with a silver surface during their adsorption on an electrochemically treated electrode was suggested. Fastcis-trans relaxation of the adsorbed molecules1a,b and complexes (1a,b)Mg²⁺ was found. It was shown that at [1a] = 10^–5 mol L^–1 and moderate molar ratios (C _Mg/[1a] = 3/1 to 9/1) in acetonitrile solutions, (trans-1a)Mg²⁺ complexes are joined into head-to-tail type dimers. An excess of Mg²⁺ cations (C_Mg/[1a] > 100) leads to dissociation of the dimers yielding (trans-1a)(Mg²⁺)₂ complexes. The formation of dimers from complexes (trans-1a)Mg²⁺ is accompanied by a substantial distortion of the planar structure oftrans-1a. This may be an important factor influencing the efficiency of photocycloaddition involving dimers of (trans-1a)Mg²⁺.For part 15, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2429–2436, December, 1995.The work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 94-03-08760) and, to some extent, of INTAS (Grant No. 93-1829) and of the International Science Foundation (Grant No. MHAOOO).