Charge-transfer complexes of benzanilides with π-acceptors

Spectrophotometric studies of several substituted benzanilides as electron donors with tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as electron acceptors have given results that are consistent with an interpretation of 1:1 charge-transfer (CT) complexes. The nature of interaction as well as the substituent effects on the CT complexation are discussed.     

Charge-transfer interactions between piperidine as donor with different σ- and π-acceptors: Synthesis and spectroscopic characterization

Charge-transfer (CT) complexes formed between piperidine (Pip) as donor with monoiodobromide (IBr), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,6-dichloroquinone-4-chloroimide (DCQ), and 2,6-dibromoquinone-4-chloroimide (DBQ), as acceptors have been studied spectrophotometrically. The synthesis and characterization of piperidine CT-complexes of monoiodobromide, [(Pip)(IBr)], 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, [(Pip)(DDQ)], 2,6-dichloroquinone-4-chloroimide, [(Pip)(DCQ)] and 2,6-dibromoquinone-4-chloroimide, [(Pip)(DBQ)] were described. These complexes are readily prepared from the reaction of Pip with IBr, DDQ, DCQ and DBQ within CHCl₃ solvent. IR, UV–Vis techniques and elemental analyses (CHN), characterize the four piperidine charge-transfer complexes. Benesi–Hildebrand and its modification methods were applied to the determination of association constant (K), molar extinction coefficient (?).     

Spectroscopic studies on the interaction of cimetidine drug with biologically significant σ- and π-acceptors

Spectroscopic studies revealed that the interaction of cimetidine drug with electron acceptors iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted through the initial formation of ionic intermediate to charge transfer (CT) complex. The CT-complexes of the interactions have been characterized using UV–vis, ¹H NMR, FT-IR and GC–MS techniques. The formation of triiodide ion, I₃^?, is further confirmed by the observation of the characteristic bands in the far IR spectrum for non-linear I₃^? ion with C_s symmetry at 156 and 131 cm^?1 assigned to ν_as(I–I) and ν_s(I–I) of the I–I bond and at 73 cm^?1 due to bending δ(I₃^?). The rate of formation of the CT-complexes has been measured and discussed as a function of relative permittivity of solvent and temperature. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants and this observation was further supported by spectral studies. Based on the spectroscopic results plausible mechanisms for the interaction of the drug with the chosen acceptors were proposed and discussed and the point of attachment of the multifunctional cimetidine drug with these acceptors during the formation of CT-complex has been established.     

Synthesis,spectroscopic and thermal structural investigations of the charge-transfer complexes formed in the reaction of 1-methylpiperidine with σ- and π-acceptors

The reactions of the electron donor 1-methylpiperidine (1MP) with the π-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil = CHL) and iodine (I₂) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. The obtained results showed that the stoichiometries of the reactions are not fixed and depend on the nature of the acceptor. Based on the obtained data, the formed charge-transfer complexes were formulated as [(1MP)(TCNE)₂], [(1MP)(DDQ)]·H₂O, [(1MP)(CHL)] and [(1MP)I]I₃, while in the case of 1MP–TCNQ reaction, a short-lived CT complex is formed followed by rapid N-substitution by TCNQ forming the final reaction products 7,7,8-tricyano-8-piperidinylquinodimethane (TCPQDM). The five solids products were isolated and have been characterized by electronic spectra, infrared spectra, elemental analysis and thermal analysis.     

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.

     

Utility of certain σ- and π-acceptors for the spectrophotometric determination of ganciclovir in pharmaceutical formulations

Studies were carried out, for the first time, to investigate the charge-transfer reactions of ganciclovir as n-electron donor with the σ-acceptor iodine and various π-acceptors: 7,7,8,8-tetracyanoquinodimethane; tetracyanoethylene; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; p-chloranilic acid; 2,3,5,6-tetrabromo-1,4-benzoquinone; 2,3,5,6-tetrachloro-1,4-benzoquinone and 2,4,7-trinitro-9-fluorenone. The formation of the colored charge-transfer complexes was utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of ganciclovir in pure form as well as in its pharmaceutical formulation (capsules). Different variables affecting the reactions were studied and optimized. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9993-0.9998) were found between the absorbance and the concentration of ganciclovir in the range of 2.0-240 μg mL⁻¹. For more accurate analysis, Ringbom optimum concentration range was found to be between 5.0 and 225 μg mL⁻¹. The limits of detection ranged from 0.36 to 2.45 μg mL⁻¹ and the limits of quantification ranged from 1.20 to 8.17 μg mL⁻¹. A Job's plot of the absorbance versus the molar ratio of ganciclovir to each of acceptors under consideration indicated (1:1) ratio. The proposed methods were applied successfully for simultaneous determination of ganciclovir in capsules with good accuracy and precision and without interferences from common additives. The recovery percentages ranged from 99.45 ± 0.73% to 100.35 ± 1.40%. The results were compared favourably with the reported method.     

Molecular complexes of quinones: I. π-π complexes of p-chloranil with benzene and its derivatives

The relation between the position of the charge transfer band of molecular complexes formed by p-chloranil with benzene derivatives and ionization potentials of the donor molecule was analyzed. Electronic absorption spectra of p-chloranil complexes with donor molecules possessing degenerate molecular orbitals were examined. Unlike complexes with other acceptors, such as 1,3,5-trinitrobenzene and 1,3-dinitrobenzenea, molecular complexes of p-chloranil with analogous donors were classed within a single group.     

Synthesis and thermal decomposition kinetics of two lanthanide complexes with cinnamic acid and 2,2′-Bipyridine

The two complexes of [Ln(CA)₃bipy]₂ (Ln = Tb and Dy; CA = cinnamate; bipy = 2,2′-bipyridine) were prepared and characterized by elemental analysis, infrared spectra, ultraviolet spectra, thermogravimetry and differential thermogravimetry techniques. The thermal decomposition behaviors of the two complexes under a static air atmosphere can be discussed by thermogravimetry and differential thermogravimetry and infrared spectra techniques. The non-isothermal kinetics was investigated by using a double equal-double steps method, the nonlinear integral isoconversional method and the Starink method. The mechanism functions of the first decomposition step of the two complexes were determined. The thermodynamic parameters (ΔH ^≠ , ΔG ^≠ and ΔS ^≠ ) and kinetic parameters (activation energy E and the pre-exponential factor A) of the two complexes were also calculated.     

Hydrocarbon (π- and σ-) complexes of nickel,palladium and platinum: Synthesis,reactivity and applications

With the exception of metallocenes, transition metal complexes with hydrocarbon ligands only are rare. However, complexes of this type containing Group 10 metals are known and have been shown to be quite stable. These complexes are versatile precursors for many organometallic compounds. In addition, such compounds can play an important role in many reactions including C–H or C–C activation reactions and have useful applications in the thermal and photochemical production of metal films by chemical vapour deposition (CVD). The present review summarizes the synthesis, properties and chemistry of hydrocarbon complexes of Group 10 metals of the type L_nM or L_nMR₁R₂ (where L_n = σ- or π-hydrocarbon ligands; M = Ni, Pd and Pt; R₁, R₂ = σ-hydrocarbon ligands) without the involvement of any hetero donor ligands such as N, P, O and S in the metal coordination spheres.     

Studies on organolanthanide complexes: VIII. Synthesis and thermal decomposition of new σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes

1,1′-Trimethylenedicyclopentadienyl-early lanthanide chlorides, [C₅H₄CH₂)₃-C₅H₄]LnCl · THF, in THF at −70°C reacted with aryllithium or alkyllithium, producing seven new THF solvated LnC σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes. The yttrium analogue was also synthesized. Their structures were determined by elemental analysis, infrared spectra, mass spectra, ¹H NMR and thermoanalyses. The thermal decomposition of the complexes obtained was studied at ambient temperature or 100°C.     

Synthesis and properties of conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains

A versatile synthetic route to conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains was developed, and new ruthenium complexes with various ligands were synthesized and characterized. These bimetallic complexes showed a remarkable absorption in the visible region (λ_max: 452-483 nm), and undergo trans-to-cis isomerization under UV light irradiation for short time. Electrochemical study showed that the metal centers in bimetallic complexes containing the CHCHC₆H₄NNC₆H₄CHCH bridge interact with each other.     

Structure,spectral and thermal characteristics of zinc(II) halide complexes with N,N-dimethyl-N′,N′-dimethylthiocarbamoyl sulfenamide

We have studied the spectral (IR, PMR, EAS) and thermal properties of new ZnX₂ complexes (X = Cl, Br, I) with N,N-dimethyl-NN,NN-dimethylthiocarbamoyl sulfenamide (L). We have established that the {[ZnLX₂]}₂ compounds obtained are dimers with Zn—X bridging bonds and monodentate coordination of L through the thione sulfur atom.     

Thermodynamic characteristics of the formation of α- and β-cyclodextrin complexes with lumichrome, lumazine, and uracil in aqueous solution

Interactions of α- and β-cyclodextrins with lumichrome and its structural fragments, lumazine and uracil, were studied by means of solubility and 1H NMR spectroscopy. α-Cyclodextrin was found to have a weak complexing ability toward the studied compounds. It was established that β-cyclodextrin forms stable complexes with lumichrome and does not complex with lumazine and uracil. It was shown that only the benzene ring of lumichrome penetrates the β-cyclodextrin cavity, leading to a substantial increase in the solubility of lumichrome in water. We concluded that β-cyclodextrin complexation with lumichrome is highly exothermic due to the van der Waals interactions and hydrogen bonding between polar groups of the reagents.     

Bond energies, reaction volumes, and kinetics for σ- and π-complexes of MoCO5L

The photosubstitution reactions of molybdenum hexacarbonyl with σ and π donor ligands were investigated using photoacoustic calorimetry and computational methods in a series of linear alkane solvents (pentane, hexane, heptane, octane, decane, and dodecane). The results show that reaction volumes make a significant contribution to the photoacoustic signal and must be considered during thermodynamic calculations based on photoacoustic measurements. The enthalpies of CO substitution by an alkane solvent and subsequent substitution by each Lewis base were determined. Corresponding Mo-L bond energies (kcal mol(-1)) were calculated: L = linear alkanes (13), triethylsilane (26), 1-hexyne (27), 1-hexene (27), and benzene (17). The relative energies are in agreement with computational results. The experimental reaction volume for CO substitution by alkane was positive (15 mL mol(-1)) and negative or close to zero for alkane substitution by a Lewis base (for example, -11 mL mol(-1) for triethylsilane and 3.6 mL mol(-1) for benzene). The errors in the experimental and computational reaction volumes are large and often comparable to the reaction volumes. An improved calibration of the methods as well as a better understanding of the underlying physics involved is needed. For the Lewis bases reported in this study, the second-order rate constants for the displacement of a coordinated alkane are less than diffusion control (5 × 10(6)-4 × 10(7) M(-1) s(-1)) and decrease monotonically with the alkane chain length. The rate constants correlate better with steric effects than with bond energies. An interchange mechanism is consistent with the results.     

Synthesis of π-conjugated, pyridine ring functionalized bis-terpyridines with efficient green, blue, and purple emission

A large variety of rigid, π-conjugated, pyridine ring functionalized bis-terpyridines are synthesized efficiently using tandem Miyaura/Suzuki-type cross-coupling reaction. Photophysical property study reveals that the absorption and luminescent properties of the obtained bis-terpyridines are profoundly affected by the nature of the functional groups at the peripheral pyridine and the spacers. Namely, by tailoring precisely the structures, the light-emitting efficiencies of bis-terpyridines can be enhanced significantly with quantum yields (Φ_f) of up to 0.62, and the emission colors can be tuned to display distinct colors including purple, bright blue, and bright green. Consequently, the novel bis-terpyridines are attractive ligands for the assembly of new metallo-supramolecule based functional materials.     

Interactions of amphiphilic drugs withα-,β-, andγ-cyclodextrins

The association of several amphiphilic drugs with -, -, and -cyclodextrins has been measured by use of drug-sensitive electrodes. Drugs investigated are hydrochlorides of chlorpromazine, dibucaine, tetracaine, and procaine, and valethamate bromide. Each drug forms the drug:cyclodextrin=11 complex with - and -cyclodextrin, and both the 11 and 21 complex with -cyclodextrin, except valethamate which only forms the 11 complex. The strength of the 11 complex formations is in the order of CyD>-CyD>-CyD. The association constant of the 21 complex in drug--CyD is larger than that of 11 complex. The free energy change of the conplex formation has a positive correlation with that of the micelle formation of drugs. The deviation from this relation is explained in terms of fittability of the bulky hydrophobic group of drugs into the cyclodextrin's cavity. The free energy change for the complex formation between chlopromazine or valethamate and -CyD is governed by the enthalpy term and not by the entropy term which controls the surfactant--CyD interactions.