Charge Transfer Complexes Of Iodine Research Articles

Kinetics of the toluene-iodine complex formation as revealed by Raman spectroscopy

The kinetics of formation of the toluene—iodine charge-transfer complex has been investigated using Raman spectroscopy of the iodine vibrational line. Using low donor concentrations, the non-reactive part of the line profile can be separated out from the total lineshape with the aid of the inverse Fourier transforms of the Raman spectrum. The remaining part arises in the complex formation and dissociation process only, and can be used to extract the complex lifetime. Spectra were recorded at 300 K from a solution of iodine dissolved in dilute (0–3 volume%) mixtures of the donor in n-heptane used as an inert solvent. Using for the equilibrium constant the value 0·500 l mol−1 obtained by Childs using the polyiodide solubility method, the lifetime of the toluene—iodine complex as determined from the residual linewidth of the reactive part of the total line profile is found to be 0·9−0·2 +0·3 ps. The equilibrium constant value of 0·315 l mol−1 obtained by Childs using the spectroscopic method is not consistent with a simple two-state model. The meaning of the concept of the lifetime of the complex is discussed. It is argued that it may describe the influence of several different processes, including both true dissociation of the complex and non-reactive collisions between the iodine and the donor molecules.

The synthesis and structural characterization of a charge transfer complex of iodine and indole trimer

− residues and organic molecules is evidenced. The structure consists of stacked molecules of indole trimers (cations) and columns of iodines (anions).

Surface enhanced Raman study of the pyridine—iodine charge transfer complex on the silver electrode

The surface enhanced Raman spectra (SERS) of the pyridine—iodine charge transfer complex on the Ag electrode were identified. As compared with the well known SERS of pyridine, the ν 1, ν 6a and ν 12 modes are blue-shifted. This is also confirmed from the comparison of the infrared absorption spectra of pyridine—iodine crystalline complex and pyridine. The origin of the blue shift and other characteristics of the SERS spectra of the complex are discussed. An attempt to observe the SERS spectra of the iodine moiety of the complex was unsuccessful. This is attributed to the short range effect of the charge transfer mechanism of SERS.

On the structure of iodine charge-transfer complexes in solution

Femtosecond transient absorption studies of charge-transfer complexes of I 2 with hexamethylbenzene have been performed in a series of noncomplexing solvents. Anisotropy measurements of the bleach of the charge-transfer absorption band indicate that the geometry and electronic structure of the complex is dependent upon the solvent environment. The results are interpreted as favoring an oblique, nearly axial, geometry in alkanes and a resting geometry in chlorinated methanes.

Temperature dependence of low-frequency electrical conductivity of the poly(phenylacetylene)-iodine charge-transfer complex in solution

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solutions has been measured at the frequency of 10 kHz, in the temperature range from − 15 to 40 °C. The data have been analysed in the light of current theories of polyelectrolyte solutions, considering the effect of counterions along the charged polymer chain. Our results show a linear dependence of electrical conductivity on the polymer concentration at an I 2 doping concentration of 10 mg/ml. These data can be accounted for by considering an electronic charge distributed over, on average, a polymer segment containing six monomers.

Charge-transfer complexes of iodine and nonionic surfactants: Interpretation and use in the Winkler method

Formation constants ( K c) and molar absorption coefficients (ϵ c) of complexes of iodine and various nonionic surfactants were determined, providing a basis for selection of a surfactant for use in a spectrophotometric modification of the Winkler method. The method of calculation of K c and ε c was extended to include absorption by triiodide at the wavelength of maximum absorbance of the complex. Because the molar absorption coefficients of polyoxyethylene 10 oleyl ether (oleth 10) and polyoxyethylene 23 oleyl ether were significantly greater than those of other surfactants, they are superior candidates for use in the Winkler method. Formation constants could not be correlated with molecular characteristics of the surfactants such as alkyl chain or polyoxyethylene chain length, nor with physical characteristics of iodine—surfactant solutions such as reduction of iodine loss due to volatilization.

X‐ray Diffraction Studies on the Molecular Semiconductors Based on the Charge‐Transfer Complexes of Some Substituted Phenothiazines with Iodine

AbstractThe powder X‐ray diffraction data on some molecular semiconductors based on the charge transfer complexes of three substituted phenothiazines viz., phenothiazine (PTZ), 2‐chlorophenothiazine (CPZ), and 2‐(trifluoromethyl)phenothiazine (TPZ) with molecular iodine have been reported in this paper. The indexing of the data has been done by Ito's method. All the complexes have been found to have orthorhombic crystal structures. The lattice parameters for the individual complexes are as follows: equation image .These results indicate that the segregated stacking of mixed valence with neutral and cationic donor moieties and polymeric iodide species, two pentaiodides linked with one trüodide forming a staircase delocalized structure, are present in these complexes. This may be possibly the reason for high electrical conductivity of these complexes. However, the charge transfer complexes of iodine with 2‐acetylphenothiazine (APZ), N‐acetylphenothiazine (NAPZ) and N‐benzoylphenothiazine (NBPZ) give no diffraction patterns indicating that the molecular semiconductors based on these complexes exist in amorphous form. This is further supported by very low electrical conductivities of these complexes. This structural information is quite useful in discussing the electronic properties of this class of molecular semiconductors.

Solvent effect on charge transfer complexes of iodine with some pyrimidines

Abstract The charge-transfer complex formation of 5-methyl pyrimidine (MP) and 2-amino-4,6-dichloropyrimidine (ACP) with iodine has been studied spectrophotometrically in CCl 4 , CHCl 3 and 1,2-dichloroethane. The results show that the complexes are of n − σ* type. Also, the K ct , Δ H ° and λ ct of the complexes vary markedly with the solvent. The results of the solvent effect are discussed in terms of solute—solute and solute—solvent competing equilibria.

UV Absorption spectra of charge-transfer complexes of iodine with some derivatives of epoxycyclohexane and of glycidyl ether

UV spectroscopy has been used to study the relative donor power of some derivatives of epoxycyclohexane and of glycidyl ether in the formation of charge-transfer complexes (CTC) with iodine. It is shown that the introduction of a second epoxycyclohexane fragment into the molecule of a substituted 1,2-epoxycyclohexane considerably increases the stability of complexes with molecular iodine, and that the donor power of aromatic derivatives of glycidyl ether considerably exceeds that of their structural analogs, derivatives of anisole.

Iodine- or Iodine Monobromide-Catalyzed Alkoxy–Alkoxy Exchange Reactions of Alkylalkoxysilanes: Formation of the Catalyst–Alkoxysilane Complexes and the Reaction Mechanism

Abstract The formation of charge-transfer complexes of iodine and of iodine monobromide with alcohols and alkoxysilanes has been established spectroscopically, and the formation constants of iodine–ethoxytriethylsilane and iodine–diethoxydimethylsilane complexes has been determined as 0.55±0.01 and 0.61±0.02, respectively. On the basis of these observations and the kinetic information recently reported, the previously proposed mechanism for the iodine or iodine monobromide catalyzed alkoxy–alkoxy exchange reactions of alkoxysilanes is discussed afresh. It has been confirmed that a mechanism involving a four-centered transition state containing a CT-complex is most favorable.

Studies of charge transfer complex equilibria on iodine-thiazoles by constant activity method

The iodine charge transfer complexes of thiazole, 4-methylthiazole, 2,4-dimethylthiazole, and benzothiazole in carbon tetrachloride have been studied by the constant activity method. The equilibrium characteristics of the CT complexes formed were measured. It was concluded that the CT complexes are of the n-σ* nature and the donating site for the charge transfer interaction is the lone pair of electrons on the nitrogen atom. Moreover, the effect of substitution on the CT equilibrium was also studied. The equilibrium constants have been found to be satisfactorily correlated with the pK values of the respective thiazole derivatives. This can be attributed to the lone pair of electrons on nitrogen being more localized on increasing the donating power of substituent. Hence, the electron density on the nitrogen atom increases and an increase in equilibrium constant was seen.

129I Mössbauer Spectroscopic Study of Several n-σ Charge-Transfer Complexes of Iodine with Thioethers

Abstract 129I Mössbauer studies have been made of n-σ charge-transfer complexes of iodine with thioethers, such as thiane, 1,4-oxathiane, and 1,4-dithiane. The spectra of these complexes consist of two sets of quadrupole octets, corresponding to the bridging and terminal iodine atoms. The transferred charges from the thioethers are localized on the terminal iodine atoms, and the bridging iodine atoms have slightly positive charges. This result can be well explained in terms of a covalent bond between the sulfur and bridging iodine atoms or the MO treatment of a delocalized three-center four-electron bonding. The contributions of the dative structure to the ground state are estimated to be 36, 28, and 24% for thiane–iodine, 1,4-oxathiane–iodine, and 1,4-dithiane-iodine respectively. The nature of the charge-transfer bond is discussed in comparison with amine-iodine complexes.

Gas Chromatographic Determination of Trace Amounts of Hexamethylenetetramine in Water Using an Iodine Charge-Transfer Complex

La performance de recuperation de l'hexamethylenetetramine ajoutee a l'eau en concentration de l'ordre du μg/l, est de 66 a 86% avec une deviation relative standard de 1,2 a 6%

Charge Transfer Complexes of Iodine with Oxygenated Donors-Ethers and Ketones. Transition State Structure and Dipole Moment of the Charge Transfer State

Charge Transfer Complexes of Iodine with Oxygenated Donors-Ethers and Ketones. Transition State Structure and Dipole Moment of the Charge Transfer State

129I Mössbauer Effect in Several π-σ Charge Transfer Complexes of Iodine

Abstract The 129I Mössbauer spectra at 16 K have been measured for the π-σ charge transfer complexes of iodine with benzene, coronene, perylene, and poly(p-phenylene). It is suggested that the benzene-iodine complex in benzene prepared by slow cooling consists of alternate benzene and iodine molecules with the six-fold axial symmetry. The Mössbauer spectrum for the coronene-iodine complex (1:1) shows only one chemical state of iodine. The acceptor orbital is described by only the σu-antibonding molecular orbital of iodine. The extent of charge transfer in the complex is estimated to be 0.06e− in the electronic ground state. In the poly(p-phenylene)-iodine complex the iodine exists as almost a free molecule, indicating that the interaction between the phenylene ring and iodine is very weak.

Solute–solute interaction in liquid crystal solvents: a nuclear magnetic resonance study of pyridine–iodine molecular complex in the nematic phase

1 H N.m.r. spectra of [14N]- and [15N]-pyridine partially oriented in nematic phase IV in the presence of iodine show dipolar couplings (Dij) increasing linearly as a function of iodine concentration. The spectral changes induced by iodine can be rationalized, to a first approximation, by assuming that the pyridine molecule is in equilibrium, in the oriented phase, with the pyridine–iodine charge transfer complex so that a considerable variation in the mean orientation of the pyridine moiety occurs. Attempts to reproduce the measured dipolar couplings of the exchanging complex on the basis of an average geometry and orientation afforded only dramatic distortion effects on the apparent geometry. Looking, moreover, at the geometry of [15N]pyridine in phase IV and in other liquid crystals geometrical distortions were also found, probably due to solute–solvent interactions, except for the ZLI 1167 phase, where an rα structure in close agreement with gas-phase microwave measurements was observed. The results suggest that, for pyridine in the nematic phase in the presence of iodine, at least a three-site mechanism is operating, one of the sites being the complexed pyridine.

Contact charge—transfer interaction of iodine with saturated hydrocarbons

With the help of the thermodynamic quantities just reported, the spectrophotometric properties of the contact charge-transfer complexes of iodine with saturated hydrocarbon solvents such as cyclohexane, methylcyclohexane and heptane have been calculated from the u.v. spectra of iodine in these solvents. Both the thermodynamic and spectrophotometric properties of these complexes are free from the interaction of other solvents.

Charge transfer complexes of iodine with aromatic hydrocarbons

The spectrophotometric and thermodynamic properties of charge—transfer complexes of iodine and aromatic hydrocarbons have been reinvestigated in heptane solvent to make a correlation between the oscillator strength of charge—transfer bands and the heats of formation of the complexes. The results disagree with Mulliken's prediction. An attempt has been made to calculate the thermodynamic as well as spectrophotometric properties of these complexes free from the influence of iodine—solvent interaction and the results thus obtained show a good correlation between the oscillator strength of charge—transfer bands and the heats of formation of the complexes.

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.

Mössbauer effect of 129I in n–σ and π–σ charge-transfer complexes of iodine in the frozen solution

The Mössbauer effect of 129I was applied to investigate charge-transfer complexes of the n–σ and π–σ types in the carbon disulfide frozen solution at 16 K. In the case of n–σ type complexes such as triethylamine–iodine and pyridine–iodine, two chemical species of iodine, which correspond to the bridging and terminal iodines, were observed in the Mössbauer spectra. It is elucidated that a charge-transfer bond is described as a mixture of a four-electron three-center bond and a covalent bond involving dσpσ hybrid orbitals in the bridging iodine. On the other hand, for the π–σ type complexes such as benzene–iodine and methylated benzene–iodine the Mössbauer spectra show only one chemical species of iodine. The acceptor orbital of iodine is thought to be described by an spd hybrid orbital. That is, a small amount of s and d characters contributes to the formation of the charge-transfer bond. From the Mössbauer parameters the charge densities and the charge distributions of iodine in these complexes were obtained.