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.     

Molecular complexes with aromatic cations as electron-acceptors—III. Charge-transfer spectra of substituted pyrylium thiocyanates,selenocyanates and iodides

Alkyl- and/or aryl-substituted pyrylium salts were converted, on grinding with the corresponding alkali salts, into thiocyanates, selenocyanates and iodides, whose electronic and vibrational absorption spectra were recorded. Charge-transfer bands were evidenced, even when they overlapped with absorption bands, by a compensation technique. A comparative discussion of charge-transfer spectra for pyrylium thiocyanates, selenocyanates and iodides is presented, accounting for the effect of one α- or γ-phenyl-substituent in thio- and selenocyanates which is opposite to that in the iodides. A pronounced negative solvatochromy of the CT band is observed. The donor ability of anions for the CT band of pyrylium salts increases in the order Br⁻<SCN⁻<SeCN⁻<I⁻. Correlations with ionization potentials I_D of these anions are presented, allowing an estimation of I_D's for SCN⁻ and SeCN⁻.     

Charge-transfer spectra of organometallic complexes—VII. Electron—donor—acceptor complexation of trialkyltinisothiocyanates with iodine and tetracyanoethylene

An ultraviolet-visible study of the charge-transfer interaction between R₃ SnNCS (R  Me, Et, iPr and nBu) and iodine, respectively, tetracyanoethylene has revealed that the HOMO with dominant lone pair character located on S is the preferred donor site in the electron—donor—acceptor (EDA) complexes. Formation constants of the complexes were calculated using a non-linear regression analysis of the u.v.-vis. data.     

Molecular complexes of hydrazones—VIII. Nitrofluorenes and arylhydrazones

Nitrofluorenes form π-π complexes with a series of hydrazones both in solution and in the solid state. The properties of the complexes, discussed on the basis of u.v.-vis and FT-i.r. data, suggest the presence of weak interactions, as confirmed by the formation constants and X-ray analysis. The presence of some degree of charge transfer is confirmed by ESR determinations. The X-ray analysis of the complex of benzaldehydediphenylhydrazone with 2,4,7-trinitrofluorenone is also reported.     

Molecular complexes of p-benzoquinonechlorimides with aromatic π-donors

The charge transfer spectra of molecular complexes of chloro substituted p-benzoquinone(4)-chlorimides with aromatic π-donors in cyclohexane have been studied. The interaction of 2,6-dichloro p-benzoquinone with the same set of donors has also been studied. The spectroscopic and thermodynamic data indicate that the complexes are very weak in nature. A comparison of the absorption intensities and formation constants for these complexes shows that the contribution of charge transfer forces are not the only dominant stabilising factors.     

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.     

Molecular recognition of α-amino acid esters with arylporphyrin zinc complexes

The recognition ability of 10 arylporphyrin zinc complexes with respect to glycine, -alanine, and leucine methyl esters in toluene at 20°C was studied by spectrophotometric titration. The formation of amino acid-porphyrin associates, depending on the substitution pattern in the macroring, was examined by ¹H NMR spectroscopy. The zinc complex with diarylporphyrin having hydroxy groups in the para positions of the benzene rings was found to be the best recognizing agent with respect to glycine methyl ester, while leucine methyl ester was recognized best by the complex with hydroxy groups in the ortho positions of the benzene rings.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1557–1562.Original Russian Text Copyright © 2004 by G. Mamardashvili, Storonkina, N. Mamardashvili.This revised version was published online in April 2005 with a corrected cover date.     

Palladium complexes with biological ligands—I. Equilibrium and reaction mechanism of Pd(II) complexes with ethionine

An equilibrium study has been carried out on the interaction of ethionine(eth) with Pd(II) in aqueous solution at I = 0.16 M (Cl⁻ and 25°C using potentiometic methods. It has been concluded that five complex species exist in the pH range 2.8–4.8. these species are: PdCl₃(Eth0H⁰₂, PdCl₂(Eth)⁻, PdClOH(Eth)⁻, Pd(Eth)₂(H)²⁺₂ and Pd(Eth)⁰₂. In addition, the stopped-flow method has been used to study the reaction kinetics of Pd(II) with Eth. Three kinetic steps were observed in the pH range 1–5.5. These steps are dependent on the total concentration of Eth (T_Eth) as well as the pH of the medium. The observed pseudo-first order rate constants for the three reaction kinetic steps at constant pH are expressed empirically by kⁱ_obs = m_i + m′_iT_Eth. The parameters m_i and m′_i are pH-dependent. It has been concluded that PdCl²⁻₄ and PdCl₂OH²⁻ species play an important role in the complex formation reactions with Eth. The data were interpreted in terms of the complex species obtained from the equilibrium study. cis-trans substitution reactions have been suggested to account for some kinetic steps.     

Vibrational spectra of carboxylato complexes—II. Some oxo-tetranuclear complexes

The i.r. and Raman spectra of the compounds Be₄O(OOCCH₃)₆, Be₄O(OOCCD₃)₆, Be₄O(OOCH)₆ and Zn₄O(OOCCH₃)₆ have been analysed and assigned in detail. In particular, the vibrational modes of the O(MO₃)₄ subunits, and their interactions with the carboxylate ligand vibrations, have been identified. The compound Zn₄O(OOCC₂H₅)₆ has the same oxo-centred structure as the others.     

The infrared spectra of complexes with planar dithiooxamides—III. The Ni(II) polymeric complexes

Thermal analysis, u.v. spectra and i.r. spectra are given for some nickel complexes and their isotopes of planar dithiooxamides, the results are explained by assuming planar and octahedral S,N conformations about the nickel atoms in a polymeric structure.     

Infrared intensities of charge transfer complexes—I. Iodine cyanide complexes

Infrared intensities of some ICN complexes were measured in solution, and the observed intensity changes on complex formation were explained on the basis of the electronic reorientation during molecular vibration. Formation constants were obtained as well from i.r. measurements for the purpose of the determination of equilibrium concentrations in the complex solutions.     

Molecular mechanics calculations on the differentiation of diastereomeric complexes ofcis-decalin withβ-cyclodextrin

Molecular mechanics calculations with the latest available version of Allinger's MM2 force field (MM2(91)) on the diastereomeric complexes of both enantiomeric conformations ofcis-decalin with -cyclodextrin show a small preference (1.67 kJ mol^–1) for one of them, in agreement with the available¹³C-NMR results. Calculations were found to be sensitive to the procedure used.     

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.

     

n—π electron-donor—acceptor complexes—IV. The interaction of aliphatic amines with 1,3-dicyanobenzene in n-hexane. The importance of preferred orientation in the stability of the complexes

The stability constants (K) for the electron-donor—acceptor (EDA) complexes formed between aliphatic amines as n-donors and 1,3-dicyanobenzene (1,3-DCB) have been determined in n-hexane as solvent. By means of free energy substitutent parameters and regression analysis, the electronic and steric effects of the N-amine substituents were quantitatively separated. Thus, values of log K were correlated with Taft's polar substituents, σ*, and Hancock's corrected steric substituent constants, E^C_s. Large steric effects are inferred which lead us to propose a preferential site of interaction. This preferential orientation may also explain the greater stability of the 1,3-DCB—amine complexes with respect to the corresponding 1,4-DCB—amine complexes. The proposal is supported by the excess of atomic charge predicted by the Mulliken population analysis, obtained by MNDO calculations for the acceptors and by considering that for weak n—π complexes, the electrostatic energy may be of major importance in the energy of interaction.     

Vibrational spectra of carboxylato complexes—IV. Mixed-metal and mixed-valence oxo-trinuclear complexes

Infrared spectra of mixed-metal complexes [Cr_3-nFe_nO(OOCR)₆L]⁺ (n = 1,2; R = H, CH₃; L = H₂O, γ-picoline, pyridine), and of mixed-valence complexes [Fe^III₂Fe^IIO(OOCCH₃)₆py₃], [Ru^III₂Ru^IIO(OOCCH₃)₆L₃] (L = H₂O, P(C₆H₅)₃) are reported and compared with analogous symmetrical (Cr^III)₃, (Fe^III)₃ and (Ru^III)₃ species. The effects of lowered symmetry are seen in the mixed-metal but not in the mixed-valence complexes.     

Molecular photonics of inclusion complexes of cucurbit[7]uril with 3,3′-diethylthiazolinocarbocyanine iodide

The effect of cucurbit[7]uril (Cb7) on the photonics of 3,3′-diethylthiazolinocarbocyanine iodide (Car) in water was studied by spectrofluorimetry, ns-laser kinetic spectroscopy, and quantum chemistry. The formation of an inclusion complex of Car with Cb7 was established, and the binding constant and composition of the Car@Cb7 (1 : 2) complex were determined. It was shown that Car and Car@Cb7 are able to undergo trans → cis-photoisomerization. The lifetime of the cis-isomer of free Car was found to be much shorter than that of the cis-Car form localized inside the cavity of Cb7. The energies of formation of complexes Car@Cb7 were found and the structure of the complex in the lowest excited singlet state was determined according to the quantum chemical calculations by the DFT method with the PBE functional. The trans → cis-isomerization was found to proceed via the excited singlet S1 state having the “perpendicular” conformation.     

NMR study of donor—acceptor complexes—III. 31P resonance of arylphosphines and arylphosphine chlorides and their complexes with BBr3, and BCl3.

The ³¹P NMR spectra of (4X—C₆H₄)_nPCl_3—n, (3X—C₆H₄)_nPCl_3—n (X = F, Cl, H; n = 1, 2, 3) molecules and of their donor—acceptor complexes with BBr₃ and BCl₃ are reported. The chemical shift increments on complexation δ^P—B are interpreted in terms of increased charge on the P-atom and of concomitant charge delocalisations: π(p—p)A$\text{←}\text{r}$—P and P$\text{→}\text{—}$Cl and π(p—d)A$\text{→}\text{r}$—P and P$\text{←}\text{—}$Cl in general and of mesomeric contributions in the case of the (4FC₆H₄)_nPCl_3—n compounds and their complexes.