Physicochemical properties of π-π complexes of zinctetraphenylporphyrin with aromatic molecules

Features of the solvation of zinctetraphenylporphyrin (ZnTPP) in benzene, toluene,ortho-, meta-, andpara-xylenes were studied by a thermogravimetric method. The temperature ranges of the stability and the compositions of the corresponding specific - complexes were determined from the results of the thermogravimetric investigation of the crystallosolvates of the metalloporphyrin with the solvent molecules, and the energy characteristics of the intermolecular metalloporphyrin—solvent interactions were calculated.Institute of the Chemistry of Nonaqueous Solutions, Russian Academy of Sciences, 153018 Ivanovo. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1545–1548, July, 1992.     

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.     

Synthesis and properties of new π-conjugated pyridine ligands with tetrathiafulvalene derivatives and the rhenium(I) tricarbonyl complexes

Three new π-conjugated pyridine ligands with redox-active tetrathiafulvalene (TTF) derivatives, L₁-L₃, have been synthesized and characterized. The Diels-Alder reaction is the key step for this multistep synthetic strategy. The crystal structures of L₁ and L₃ have been studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding tricarbonyl rhenium(I) complexes (ReL₁(CO)₃X, X = Cl, 5; X = Br, 6) have also been investigated.     

Influence of alkyl substituents on the π* negative ion states of benzene and its derivatives : Electron transmission spectroscopy of p-alkylanilines

Electron affinities and electron attachment energies associated with the π^* orbitals of several p-alkylanilines (alkyl = Me, Et, i-Pr, and t-Bu) have been determined in the gas phase by electron transmission spectroscopy and have been analyzed by ab initio molecular orbital calculations at the STO-3G and 6-31G levels of basis set. The results lead to the conclusions that (a) the ²A₂ negative ion state in toluene lies below the ²B₁ state, (b) the ²A₂ state is stabilized in toluene relative to benzene by bonding overlap between the ortho carbon (C₂(2p_π)) and the Me H(1s) orbitals in the LUMO, (c) the ²B₁ state is stabilized on adding Me groups to toluene to form t-butylbenzene through reduced antibonding interactions between C₁(2p_π) and Me C(2p_π) orbitals, and (d) the lowest resonance in t-butylbenzene is extensively overlapped with the second resonance and may involve strong mixing of the ²A₂ and ²B₁ states.     

Excimer fluorescence and structures of the inclusion complexes of β-cyclodextrin with naphthalene and its derivatives

Fluorescence of the inclusion complexes with different compositions formed by naphthalene-h₈, naphthalene-d₈, 2,7-dimethylnaphthalene (DMN), and 2-benzylnaphthalene (BN) with β-cyclodextrin (β-CD) in water was studied. Two types of fluorescence are observed, monomer (MF) and excimer (EF_ fluorescence. The excimer fluorescence of the 2∶2 complex emitted by aggregated light-dispersing crystals forming a precipitate, whereas is the MF is concentrations, EF predominates for the resulting complexes. A proposed structure of the inclusion complexes was derived from MNDO/PM3 semiempirical quantum-chemical calculations. The EF is caused by the structure of the complex, in which both naphthalene molecules are separated by a distance of 4.7 Å: they lie in parallel orientation to each other, whereby one ring is displaced from the other by one-fourth of the length of the naphthalene ring. The complexes of 2,7-DMN and 2-benzylnaphthalene with β-CD do not exhibit EF. For the 2∶2 complex of 2,7-DMN with β-CD, this is due to the fact that the aromatic fragments are removed too far from one another 2-Benzylnaphthalene is unable to form an inclusion complex with β-CD, in whose structure the aromatic fragments inside the cavity could be arranged in parallel planes; instead, it forms a 1∶2 complex with β-CD.     

Molecular complexes of cyclophanes—XIII. Charge-transfer complexes of cyclophanes with fluoranil

The charge-transfer (CT) complexes of some methylated [2.2]para-, multibridged cyclo- and [2.2]indenophanes as π-donors with fluoranil (TFQ) as π-acceptor have been studied spectrophotometrically. The role of the molecular structure of the donors on their Lewis basicities and stability of their CT complexes with TFQ are discussed. Eight pure crystalline complexes were prepared. Their i.r. spectra indicate an increase of the electron density in the TFQ part of the CT complex.     

Charge transfer adducts of metal complexes of π-donor ligands with I2 and TCNQ

Copper(II) and nickel(II) biguanides and O-alkyl-1-amidinourea can act as donors for the formation of charge transfer (CT) adducts with I₂ and tetracyanoquinodimethane (TNCQ) as acceptors. Iodine adducts are characterized both in solid and solution states whereas TCNQ adducts obtain only in solution. Appearance of a broad band at 355 nm for iodine adducts and at 335 nm for TNCQ adducts and shifting of i.r. frequencies support the formation of donor acceptor associates. Elemental analysis establishes 1:1 stoichiometry of the solid adducts. The K and ε values determined by modified Benesi—Hildebrand, Scott and Rose—Drago equations are found to be of the order of 10⁴ and 10³ respectively at 298 K in methanol. The solvent effect on the K values is discussed in terms of coupled solute-solute and solute-solvent equilibria.     

Charge transfer molecular complexes of arylidene anthranilic acid derivatives with π-electron acceptors

X-Benzylidenesanthranilic acid molecular complexes with π-acceptors, tetracyanoethylene, 2,3-dichloro-5,6-dicyano-p-benzoquinone and chloranil, have been studied. The intramolecular hydrogen bonding that exists in such compounds greatly inhibits the transition of the nitrogen azomethine n-electrons. The formation constant values and molar extinction coefficients of the p-dimethyl-aminobenzylidenean-thranilic acid-DDQ CT complexes have been determined in CH₂Cl₂, C₂H₄Cl₂ and CHCl₃ in the temperature range 10–30°C. Such CT complexes are of strong n-π type.     

Enhancing Molecular Chain Entanglement and π-π Stacking Toward the Improvement of Shape Memory Performance of Polyimide

Chinese Journal of Polymer Science - Thermoplastic polyimides (PIs) with shape memory potential have received growing attention in recent years. In this work, high-performance thermoplastic PIs...     

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.     

New mercury(II) and silver(I) complexes containing NHC metallacrown ethers with the π-π stacking interactions

The oligoether-linked bis-benzimidazolium salt 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[(3-^secbutyl)benzimidazolium-1-yl]iodide (H₂L¹ · I₂), 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[(3-ethyl)benzimidazolium-1-yl]iodide (H₂L² · I₂) and 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[(3-^secbutyl)benzimidazolium-1-yl]hexafluorophosphate (H₂L¹ · (PF₆)₂) and their three new mercury(II) and silver(I) complexes containing NHC metallacrown ethers, HgL¹ · (Hg₂ · I₆) (1), HgL² · I₂ (2) and AgL¹ · PF₆ (3) were prepared and characterized. In the packing diagrams of H₂L² · I₂, 1, 2 and 3 benzimidazole ring head-to-tail π-π stacking interactions are observed.     

On the weakly C-H···π hydrogen bonded complexes of sevoflurane and benzene

A vibrational assignment of the anaesthetic sevoflurane, (CF(3))(2)CHOCH(2)F, is proposed and its interaction with the aromatic model compound benzene is studied using vibrational spectroscopy of supersonic jet expansions and of cryosolutions in liquid xenon. Ab initio calculations, at the MP2/cc-pVDZ and MP2/aug-cc-pVDZ levels, predict two isomers for the 1?:?1 complex, one in which the near-cis, gauche conformer of sevoflurane is hydrogen bonded through its isopropyl-hydrogen atom, the other in which the same conformer is bonded through a bifurcated hydrogen bond with the fluoromethyl hydrogen atoms. From the experiments it is shown that the two isomers are formed, however with a strong population dominance of the isopropyl-bonded species, both in the jet and liquid phase spectra. The experimental complexation enthalpy in liquid xenon, ΔH(o)(LXe), of this species equals -10.9(2) kJ mol(-1), as derived from the temperature dependent behaviour of the cryosolution spectra. Theoretical complexation enthalpies in liquid xenon were obtained by combining the complete basis set extrapolated complexation energies at the MP2/aug-cc-pVXZ (X = D,T) level with corrections derived from statistical thermodynamics and Monte Carlo Free Energy Perturbation calculations, resulting in a complexation enthalpy of -11.2(3) kJ mol(-1) for the isopropyl-bonded complex, in very good agreement with the experimental value, and of -11.4(4) kJ mol(-1), for the fluoromethyl-bonded complex. The Monte Carlo calculations show that the solvation entropy of the isopropyl-bonded species is considerably higher than that of the fluoromethyl-bonded complex, which assists in explaining its dominance in the liquid phase spectra.     

Long-lived phosphorescence of aqueous solutions of β-cyclodextrin complexes with naphthalene and its derivatives at room temperature

A long-lived phosphorescence at room temperature (lifetime>1 s) of aqueous solutions of β-cyclodextrin complexes with naphthalene and its derivatives was found. The phosphorescence isobserved for aggregated complexes that form in water a light-scattering suspension, and its low intensity is due to predomination of 2∶2 complexes with efficient excimer fluorescence. Complexes containing isolated aromatic molecules are assumed to be the centers of fluorescence. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2022–2024, October, 1999.     

Some peculiarities of π—π interactions between tetraphenylporphine metal complexes and aromatic solvents

The — complexes of metal tetraphenylporphinates with benzene, toluene, and xylenes were characterized by means of thermogravimetry. The ability of metalloporphyrins to form — complexes with certain -donor molecules depends largely on the -acceptor capacity of the macroheterocycle, and on the peculiarities of the metal—porphyrin coordinative linkage. Stoichiometry, energy parameters, and thermal stability of the - complexes of metalloporphyrins with various aromatic ligands are determined to a great extent by the molecular structure of solvents.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp.850–853, May, 1993.     

Conformation of aromatic rings in isolable atropisomers of 2-arylindoline derivatives and kinetic evidences for π-π interaction

The equilibrium constants [K=anti/syn] of a pair of atropisomers due to restricted rotation about Csp³-Csp² bond for [2-(2-hydroxynaphthalen-1-yl)-3,3-dimethylindolin-1-yl](4-substituted phenyl)methanone were determined in some solvents. The presence of the effective π-π interaction was demonstrated by the correlation between the equilibrium constants (K) and the substituent effect of the phenyl groups (σ_p), suggesting that the ‘neutral-type’ interaction is operative.     

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.     

Metal π complexes of benzene derivatives: Part 56. (η6-Fluoranthene)(tricarbonyl)chromium: isomerism and haptotropic equilibration

Reaction of fluoranthene with Cr(CO)₃Py₃/BF₃·OEt₂ at 25 °C affords a mixture of two isomeric complexes: traces of tricarbonyl(1-5,15-η⁶-fluoranthene)chromium (3) (coordination to benzene) and, as the major product, tricarbonyl(1-4,15,16-η⁶-fluoranthene)chromium (2) (coordination to naphthalene). The ratio 3:2 is less than 0.05 according to ¹H-NMR of crude product before crystallization. Complex 2 is thermodynamically less stable than 3: at 100 °C in decane or C₆D₆ for 8 h or at 90 °C in C₆F₆ for 100 h 2 rearranges irreversibly to 3 via an inter-ring haptotropic shift of the Cr(CO)₃ group from the naphthalene moiety to the benzene part of the fluoranthene ligand. NMR evidence for a degenerate reversible haptotropic shift within the naphthalene moiety is absent. The isomers 2 and 3 have been characterized by X-ray structural analysis.     

Organometallic dithiolene complexes of benzenedithiolate analogues with π-coordinating and π-interacting Cp* ligand

Organometallic dithiolene complexes, which were formulated as [Cp*M(dcbdt)] and [Cp*M(dcdmp)] (M = Co, Rh, Ir; Cp* = η⁵-pentamethylcyclopentadienyl, dcbdt = 4,5-dicyanobenzene-1,2-dithiolate, dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine) were prepared from a low valent Cp*Co^I or high valent Cp*M^III species (M^III = Co^III, Rh^III, Ir^III). The UV-Vis absorption spectral and electrochemical data of them were obtained. The lowest absorption (HOMO-LUMO) energies of them became redshift in order of the Co > Rh > Ir complexes. The reduction potentials suggested that the central metal modifies their LUMO levels. The molecular and crystal structures of [Cp*Co(dcbdt)] (3a), [Cp*Co(dcdmp)] (4a) and [Cp*Rh(dcdmp)] (4b) were determined by X-ray diffraction studies. The cobalt complexes 3a and 4a were monomeric, formally 16-electron complexes and have two-legged piano-stool geometries. The crystal structure of 3a indicated some plane-to-plane intermolecular interactions such as benzene?benzene interaction on the dcbdt ligand and two Cp*?benzene π-π stackings. 4a showed plane-to-plane interaction with a pseudo-4-fold-symmetry arrangement between the pyrazine moieties on the dcdmp ligand. The rhodium complex 4b was dimeric in the crystal to form a criss-cross arrangement and had a three-legged piano-stool geometry, but it was monomerized in solution. The dimer of 3b was observed in the oxidation process of the cyclic voltammogram.     

Reaction of nitroalkanes with levoglucosenone and its α-bromo and α-iodo derivatives. Cyclopentaannulation of α-halocyclenones

Michael reactions of levoglucosenone and its α-bromo and α-iodo derivatives with α,ω-dinitroalkanes were studied under conditions of chemical and electrochemical generation of base. Procedures were developed for stereospecific fusion of a cyclopentane ring to α-bromo- and α-iodolevoglucosenones, 2-iodocyclopent-2-en-1-one, and 2-iodocyclohex-2-en-1-one by the action of 2,2-dimethyl-1,3-dinitropropane.