Raman spectra and molecular orientation of 7,7′,8,8′-tetracyanoquinodimethane in thin films evaporated on aluminum

Raman spectra of thin films of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) evaporated in vacuo on aluminum mirrors were measured with external reflection method. Raman intensity was dependent on polarization of the incident laser beam, collection angle of the scattered light, and molecular orientation of the surface species. The optimum conditions for observing Raman spectra of a thin film on metal surface were discussed experimentally and theoretically.From the collection angle dependence of Raman intensity, it is deduced that the aromatic ring of TCNQ is oriented almost parallel to the metal surface.     

Mixed valence copper(I)–copper(II) complexes of N,S donor ligands and their 7,7′,8,8′-tetracyanoquinodimethane derivatives

The reaction of the CuCl2·2H2O with the N,S donor ligands bis(o-aminobenzenethio)ethane, bis(o-aminoben-zenethio)propane and bis(o-aminobenzenethio)butane (abbreviated as eN2S2, pN2S2 and bN2S2, respectively) yielded mononuclear CuII complexes of stoichiometry Cu(L)Cl2 (L=eN2S2, pN2S2 or bN2S2). When the reactions were performed in the presence of 2,6–diacetylpyridine and NaClO4, binuclear mixed valence CuI–CuII complexes of stoichiometry [Cu2(L)][ClO4]3 (L=eN6S4, pN6S4 or bN6S4) were formed. Metatheses between the binuclear complexes and the lithium salt of 7,7,8,8-tetracyanoquinodimethane (TCNQ) yielded complexes of stoichiometry Cu2(L)(TCNQ)2 (L=eN6S4, pN6S4 or bN6S4). All of the complexes were characterised by analytical and spectroscopic techniques.     

Spectroscopic studies on the electron donor—acceptor interaction between piperidines and tetrachloro-1,2-benzoquinone

The title interaction has been studied in chloroform medium. The 2:1 charge-transfer (CT) complex formed between the donor and acceptor is stable in excess acceptor concentrations, but transforms to a disubstituted product in excess donor concentrations. The u.v.—vis and ¹H NMR spectral data for the CT complexes and the solvent effect on the electronic transition of the CT have been presented and discussed.     

A comparison of the asymmetric hydrogenation catalyzed by rhodium complexes containing chiral ligands with a binaphthyl unit and those with a 5,5′,6,6′,7,7′,8,8′-octahydro-binaphthyl unit

The chiral ligands H₈–BINAPO and H₈–BDPAB were synthesized by reacting chlorodiphenylphosphine with H₈–BINOL and H₈–BINAM, respectively. Applications of these ligands in the Rh-catalyzed enantioselective hydrogenation of a variety of (Z)-acetamido-3-arylacrylic acid methyl esters provided chiral amino acid derivatives with good to excellent enantioselectivities (H₈–BINAPO: up to 84.0% e.e.; H₈–BDPAB: up to 97.1% e.e.). In the hydrogenation of acetamidoacrylic acid, 99% e.e. was obtained when a [Rh(H₈–BDPAB)]⁺ catalyst was used. The catalytic activities and enantioselectivities of [Rh(H₈–BINAPO)]⁺ and [Rh(H₈–BDPAB)]⁺ are substantially better than those obtained with the corresponding rhodium catalysts containing BINAPO (up to 64% e.e.) and BDPAB (up to 92.6% e.e.).     

Spectroscopic studies on the electron donor—acceptor interaction between 1-propanamine-3-triethoxysilyl and π-acceptors

The spectrophotometric properties of the title interaction have been studied in methylene chloride. 2:1 charge-transfer (CT) complexes were formed between the acceptors and the donor, except with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) a 4:1 complex was formed between the acceptor and the donor. The UV—vis. and IR spectral data for the CT complexes and the solvent effect on the electronic transition of the CT have been presented and discussed. The ionization potential of the donor was determined.     

Spectroscopic studies of multiple charge transfer complexes of p-toluidine with π-acceptor picric acid in different polar solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to be 1: 1 ratio by straight line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K _CT), molar extinction coefficient (?_CT), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R _N) and ionization potential (I _D). The results indicate that the formation constant (K _CT) for the complex were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used.     

Spectroscopic studies on the inclusion behavior between caffenic acid and ��-cyclodextrin

To investigate the inclusion ability of ??-cyclodextrin (??-CD) for caffenic acid (CA). The conditions for the formation of inclusion complex and the binding constant between ??-CD and CA were determined by fluorescent and ultraviolet spectroscopic methods. The behavior of CA as a free radical scavenger before and after its inclusion was investigated. In addition, solid samples of the inclusion complex, prepared through the co-precipitation and grinding methods, were characterized via IR spectroscopy and differential scanning calorimetry. The inclusion complex was further characterized with ¹H NMR spectroscopy. By using fluorescent and ultraviolet spectroscopy, the conditions for the formation of inclusion complex between ??-CD and CA were optimized and the binding constant determined. It was observed that the guest molecule behaves as a better anti-oxidant after its inclusion into ??-CD.     

413 — Biocatalytic oxidation of glucose on the conductive charge transfer complexes

Glucose oxidase entrapped in the layer near the electrode surface of conductive charge-transfer complexes or on glassy carbon electrodes modified by tetracyano-quinodimethane (or by its K-salt) catalyzes the electrochemical oxidation of glucose in the interval from −0.05 to 0.4 V (vs. Ag⋎AgCl). When enzyme electrodes operate in a switched-off state the charge is accumulated in the complexes. The components of the complexes oxidize the active center of glucose oxidase. A scheme for electrocatalytic oxidation of glucose by mediators is proposed.     

Theoretical investigation on the structural and electronic properties of complexes formed by thymine and 2′-deoxythymidine with different anions

Hydrogen bonding interactions between thymine nucleobase and 2′-deoxythymidine nucleoside (dT) with some biological anions such as F⁻ (fluoride), Cl⁻ (chloride), OH⁻ (hydroxide), and NO₃ ⁻ (nitrate) have been explored theoretically. In this study, complexes have been studied by density functional theory (B3LYP method and 6-311++G (d,p) basis set). The relevant geometries, energies, and characteristics of hydrogen bonds (H-bonds) have been systematically investigated. There is a correlation between interaction energy and proton affinity for complexes of thymine nucleobase. The nature of all the interactions has been analyzed by means of the natural bonding orbital (NBO) and quantum theory atoms in molecules (QTAIM) approaches. Donors, acceptors, and orbital interaction energies were also calculated for the hydrogen bonds. Excellent correlations between structural parameter (δR) and electron density topological parameter (ρ _b) as well as between E(2) and ρ _b have been found. It is interesting that hydrogen bonds with anions can affect the geometry of thymine and 2′-deoxythymidine molecules. For example, these interactions can change the bond lengths in thymine nucleobase, the orientation of base unit with respect to sugar ring, the furanose ring puckering, and the C1′–N1 glycosidic linkage in dT nucleoside. Thus, it is necessary to obtain a fundamental understanding of chemical behavior of nucleobases and nucleosides in presence of anions.     

Solvent effect on the thermodynamic and spectrophotometric properties of charge—transfer complexes—II

The thermodynamic and spectrophotometric properties of the hexamethylbenzene—iodine charge—transfer complex in different donor solvents such as benzene, toluene, xylene (o-, m-, p-) and mesitylene are found to depend on the solvent. The results show that the oscillator strengths of the charge—transfer bands of the hexamethylbenzene—iodine complex in these donor solvents increase with the heats of formation but these values of oscillator strengths are found comparatively high in comparison with the results observed earlier in inert solvents. The charge—transfer interaction of donor solvents with iodine is responsible for changing both thermodynamic as well as spectrophotometric properties of the hexamethylbenzene—iodine complex. An attempt is made to calculate the thermodynamic and spectrophotometric properties of these complexes free from other interaction.     

Mass spectrometry and molecular modeling studies on the inclusion complexes between alendronate and β-cyclodextrin

Complexation of alendronate sodium (AlnNa) with β-cyclodextrin (β-CD) was studied by means of ESI-mass spectrometry. The experimental results show that stable 1:1 inclusion complexes between selected bisphosphonates and β-CD were formed. In addition, complexes with different stoichiometry were observed. DFT/B3LYP calculations were performed to elucidate the different inclusion behavior between alendronate and β-CD. Molecular modeling showed that the inclusion complex of Aln-β-CD where the two phosphonate groups bound to the central carbon atom of bisphosphonate were inserted into the cavity of β-CD from its “top” side was thermodynamically more favorable than when they were inserted from its “bottom” side; the complexation energy was ?74.05 versus ?60.85 kcal/mol. The calculations indicated that the formation of conventional hydrogen bonds was the main factor for non-covalent β-CD:Aln complex formation and stabilization in the gas phase.     

Synthesis and spectroscopic studies on charge-transfer molecular complexes formed in the reaction of imidazole and 1-benzylimidazole with σ- and π-acceptors

The spectrophotometric characteristics of the solid charge-transfer molecular complexes (CT) formed in the reaction of the electron donors imidazole (IML) and 1-benzylimidazole (BIML) with the σ-acceptor iodine and π-acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoethylene (TCNE) and 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL) have been studied in chloroform at 25 °C. These were investigated through electronic and infrared spectra as well as elemental analysis. The results show that the formed solid CT-complexes have the formulas [(IML)2 I]I3, [(IML)(DDQ)], [(IML)2(TCNE)5] and [(IML)(CHL)] for imidazole and [(BIML) I]I3, [(BIML)(DDQ)2], [(BIML)(TCNE)2] and [(BIML)(CHL)2] for 1-benzylimidazole in full agreement with the known reaction stoichiometries in solution as well as the elemental measurements. The formation constant KCT, molar extinction coefficient ?CT, free energy change ΔG0, CT energy ECT and ionization potential Ip have been calculated for the CT-complexes [(IML)2 I]I3, [(IML)(DDQ)], [(IML)(CHL)], [(BIML) I]I3, [(BIML)(DDQ)2], [(BIML)(TCNE)2] and [(BIML)(CHL)2].     

Spectroscopic study of charge transfer complexes of some benzo crown ethers with π-acceptors DDQ and TCNE in dichloromethane solution

Formation of the charge transfer complexes between benzo-15-crown-5, dibenzo-18-crown-6, dibenzo-24-crown-8 and dibenzo-crown-10 and the π-acceptors DDQ and TCNE in dichloromethane solution was investigated spectrophotometrically. The molar absorptivities and formation constants of the resulting 1:1 molecular complexes were determined. The stabilities of the complexes of both π-acceptors vary in the order DB18C6 > DB3OC10 ⋍ DB24C8 > B15C5. All of the resulting complexes were isolated in crystalline form and characterized. The influences of potassium ion on the formation and stability of the TCNE molecular complexes were studied. Effects of the crown ether structure and the role of the K⁺ ion on the formation of charge transfer complexes are discussed.     

Molecular complexes of cyclophanes,XVIII: Spectroscopic and thermodynamic studies on the charge-transfer complexes between 4-([2.2]paracyclophanoyl)amines and π-acceptors

The charge-transfer (CT) complexes of several substituted 4-([2.2]paracyclophanoyl)amines as donors with tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as -acceptors have been studied spectrophotometrically. The role of the molecular structure of the donors on their Lewis basicities, the site and type of CT interactions are discussed. The thermodynamic properties of some CT complexes as well as the solvent effect on the CT complexation are reported.

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Molekulare Komplexe von Cyclophanenen, 18. Mitt.: Spektroskopische und thermodynamische Untersuchungen der Charge-Transfer-Komplexe von 4-([2.2]Paracyclophanoyl)aminen mit -Akzeptoren

Zusammenfassung Es wurden die Charge-Transfer-Komplexe einiger substituierter 4-([2.2]Paracyclophanoyl)amine als Donoren mit Tetracyanoethylen (TCNE) und 2,3-Dichlor-5,6-dicyanobenzochinon (DDQ) als -Akzeptoren spektrophotometrisch untersucht. Der Einfluß der Donor-Molekülstrukturen auf ihre Lewis-Basizitäten sowie Ort und Typ der CT-Wechselwirkung werden diskutiert. Es wird über die thermodynamischen Eigenschaften einiger CT-Komplexe und auch über Lösungsmitteleffekte bei der Komplexierung berichtet.

     

Spectroscopic and electrochemical study of dinuclear and mononuclear copper complexes with the bidentate ligand of the 2,2′-diquinoline series

The newly synthesized complex (2) of copper(I) chloride with di-n-hexyl 2,2′-biquinoline-4,4′-dicarboxylate (L) was spectroscopically and electrochemically characterized. The X-ray diffraction study showed that the crystals of complex 2 consist of the dinuclear moieties [L₂Cu¹ ₂(μ-Cl)₂] containing Cu₂(μ-Cl)₂ clusters. Spectrophotometric studies and ESI-mass spec-trometric measurements showed that after the dissolution of complex 2 in acetonitrile (AN) and N-methyl-2-pyrrolidone (NMP), the solution contained not only the dinuclear complexes [L₂Cu¹ ₂(μ-Cl)₂] but also [L₂Cu¹]Cl, [LCu¹Cl(Sol)], and [Cu¹Cl(Sol)] (Sol is the solvent). The electrochemical data also confirm the conclusion that bridged dinuclear chloride complex 2 dissociates both in NMP and AN to form the tetrahedral bis-biquinoline complex [L₂Cu¹]Cl. In solutions of complex 2 in alcohols and _N,_N-dimethylformamide (DMF), only [L₂Cu¹]Cl and [Cu¹Cl(Sol)] are present. In EtOH, AN, and DMF, [Cu¹Cl(Sol)] undergoes disproportionation to [Cu¹¹Cl(Sol)] and Cu⁰.     

Preparation and characterization of ruthenium complexes with the new 4,4′,4″-tri-tert-butylterpyridine ligand and with 4,4′-di-tert-butylbipyridine

An efficient procedure for the preparation of 4,4′,4″-tri-tert-butylterpyridine (trpy*) which is formed together with 4,4′-di-tert-butylbipyridine (bipy*) is described, and the preparation of the complexes (trpy*)RuCl₃, [(trpy*)L₂RuCl]PF₆ (L₂ = bipy, bipy*), and (bipy*)₂RuCl₂ and their characterization by cyclic-voltametry, UV—vis and ¹H NMR spectroscopy are reported. It is shown that introduction of tert-butyl substituents increases the solubility of the resultant complexes and enhances the electron donating influence of the trpy ligand.