The crystal and molecular structure of π-cyclopentadienylvanadium tetracarbonyl

The crystal structure of(π-C₅H₅)V(CO)₄ has been found from a 3-dimensional X-ray analysis. The orange crystals are orthorhombic, space group Pnma, with the vanadium atom occupying a special position on a mirror plane. The cyclopentadienyl ring was disordered ovr two equally preferred orientations. The vanadium atom and carbonyl groups are ordered. Bond lengths are compared with related structures.     

The ultraviolet and visible spectra of π-allylpalladium complexes

The UV and visible spectra (50,000-14,300 cm⁻¹ of π-allylpalladium chloride have been recorded in a number of solvents. The spectra exhibit five bands, three relatively weak bands at about 29,500 cm⁻¹, 34,000 cm⁻¹ and 40,000 cm⁻¹ which are assigned to d-d transitions and two more intense bands at about 44,000 cm⁻¹ and 46,500 cm⁻¹ which are assigned to charge transfer transitions from the chloride p_π to the palladium d_z² orbital and from the palladium d_xz to the allyl π^* orbitals respectively. The considerable dependence of the positions of the bands on the nature of the solvent used is discussed. It is suggested that in 4 M aqueous potassium chloride a dimermonomer equilibrium exists in which the dimer is the predominant species.     

The improvement of π-conjugation by the lateral benzene of anthracene and naphthalene

The 1,4-diarylnaphthalenes, 1,4-diarylanthracenes, and 9,10-diarylanthracenes containing the different side arenes, including phenyl, 2-thienyl, and 2-furyl groups, were synthesized to study the influence of structures on π-conjugation. According to photophysics and computation, the smaller dihedral angles and the lateral benzene of anthracene would increase the π-conjugation in some cases. Compared to 1,4-diarylnaphthalenes, 1,4-di(thien-2-yl)anthracene, 1,4-di(fur-2-yl)anthracene, and 9,10-di(fur-2-yl)anthracene displayed better π-conjugation in both of the ground and fluorescing excited states, but 9,10-di(thien-2-yl)anthracene only showed better π-conjugation in the fluorescing excited state.     

The reactions of metallic mercury with π-allyl compounds of Ni,Pd and Pt

The reaction of metallic mercury with π-allyl compounds of nickel, palladium and platinum has been discussed. Nickel complexes do not react with mercury but palladium and platinum derivatives give the corresponding allylmercury halides. A reaction mechanism for π-allylpalladium chloride, for example, has been suggested, that involves the cleavage of the μ-halide bridges in the (π-C3H5PdCI) molecule and π-a-perturbation in the π-allyl ligand, causing cis-migration of the σ-bonded allyl group from palladium to the mercury atom.     

Metal π-allyl chemistry II. The alkaline hydrolysis of π-allylpalladium chloride

Investigation of the alkaline hydrolysis of π-allylpalladium chloride in boiling water has shown that when the products are swept out as they are formed using oxygen-free nitrogen the oxygen-containing product of the hydrolysis is acetone. This result, together with earlier reports of acrolein and allyl alcohol as the oxygen-containing hydrolysis products, suggests that the reaction is more complex than previously considered.     

Energies of π*- and π-states of the conduction band and valence band of chiral carbon nanotubes

Nanotubes (NTs) are mainly represented by (n,p) chiral NTs with chirality indices 0 < p < n delimited by (n,0) and (n,n) for achiral NTs. In (n,p) chiral NTs, the unit cell hexagons have a helical arrangement on the cylindrical surface of an NT and common angular and axial translations. An analytical formula was derived for calculation of the band structure of both chiral and achiral NTs with chirality indices 0 ≤ p ≤ n and band diagrams of some chiral NTs. Chiral NTs significantly extend the range of semiconducting NTs. An equation for the band gap width ΔЕ of semiconducting chiral and achiral NTs was derived: \(\frac{{\vartriangle E}}{{{\gamma _0}}} = \frac{{2\pi }}{{\sqrt {3{n^2} + 3np + 3{p^2}} }}\). Tables of the band structure parameters of metallic and semiconducting chiral NTs are presented.     

The electron-spin resonance spectra of 1,4-dithiin radical-cations and the nature of the carbon-sulphur π-bond

The radical cations of 1,4-dithiin, 1,4-benzodithiin and thianthrene have been prepared and their electron-spin resonance spectra measured at room temperature in concentrated sulphuric acid solution. Spin densities for these radicals have been calculated using McLachlan's extension of the Hückel molecular orbital method with neglect of overlap and using two models for the sulphur atom, one with and the other without the participation of the 3d-orbitals. It is concluded that the 3d-model gives significantly better results although qualitatively a similar distribution is predicted by both models. Appropriate values for the sulphur atom parameters are those used by Longuet-Higgins in his discussion of thiophene. Owing to the probable non-planarity of these radicals the improvement arising from the inclusion of d-orbitals may in fact be due, at least in part, to interaction of the carbon 2p _zorbitals with the antibonding carbon-sulphur orbitals.

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Zusammenfassung Die Radikal-Kationen von 1,4-Dithiin, Benzo-1,4-dithiin und Thianthren wurden dargestellt und ihre Elektronenspin-Resonanz-Spektren bei Raumtemperatur in konzentrierter Schwefelsäure gemessen. Die Spindichten für diese drei Radikale wurden nach der Methode von McLachlan unter Verwendung von zwei Modellen für das Schwefelatom berechnet; das eine Modell mit und das andere ohne Beteiligung von 3d-Orbitalen. Es ergab sich, daß durch das 3d-Modell eine bessere quantitative Übereinstimmung erzielt werden kann, obwohl beide Modelle eine ähnliche qualitative Verteilung ergeben. Die geeigneten Werte für die Parameter des Schwefelatoms sind die von Longuet-Higgins in seiner Diskussion über Thiophen benutzten. Da diese Radikale wahrscheinlich nicht planar gebaut sind, können, jedenfalls teilweise, die durch die Einbeziehung der d-Orbitale erzielten Verbesserungen von einer Wechselwirkung der Kohlenstoff 2 p _z-Bahnen mit den nichtbindenden Kohlenstoff-Schwefel--Orbitalen herrühren.

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Résumé Les radicaux catioaiques de 1,4-dithiin, 1,4-benzodithiin et de thianthrène ont été préparés et leurs spectres de résonance électroniques mesurés à température ambiante en solution d'acide sulphurique concentré. Les densités de spin pour ces trois radicaux ont été calculées selon la méthode de McLachlan en utilisant deux modèles pour l'atome de soufre; l'un avec et l'autre sans la participation des orbitales 3d. Il en résulte que le modèle 3d donne un meilleur accord quantitatif, quoique les deux donnent une distribution qualitativement semblable. Les valeurs appropriées des paramètres de l'atome de soufre sont celles utilisées par Longuet-Higgins dans sa discussion du thiophène. A cause de la non-planarité de ces radicaux, l'amélioration apportée par les orbitales d pourrait être due, du moins en partie, à l'interaction des orbitales 2 p _zdu carbone avec les orbitales antiliantes carbone-soufre.

     

The Synthesis,Characterization and DC Electrical Conductivity of Polypyrrole‐Zirconium Complex

Polypyrrole‐zirconium complex has been synthesized by reacting 2‐amino‐3,4‐dicyano‐5‐mercaptopyrrole with zirconium nitrate in absolute ethanol under reflux for 24 h. The product has been characterized by elemental analyses, FTIR spectroscopy, in addition to thermal analysis (TGA and DSC) and its solubility has been investigated. The DC electrical conductivity variation of polypyrrole‐zirconium complex has been studied in the temperature range 300–500 K after annealing for 24 h at 100°C and doping with I₂, FeCl₃ and CuCl₂ · H₂O for comparison. An attempt has been made to interpret the DC electrical conductivity behavior and thermal properties to chain length, dopant used, polymer structure and attached groups.     

Theoretical study of solvent effect on π-EDA complexation II. Complex between TCNE and two benzene molecules

Formation of tetracyanoethylene—benzene 1: 1 and 1: 2 complexes was modeled using the Møller—Plesset second-order theory (MP2) and polarized continuum model (PCM). The MP2 calculated geometry of 1: 1 complex presents a plane-parallel C _2υ sandwich structure with interplanar distance 3.05 × 10^?10 m, while the 1: 2 complex has D _2h geometry where the planparallel distance is equal to 3.09 × 10^?10 m. The MP2 calculations indicate that the main part of formation enthalpy in both complexes is dispersion energy due to intermolecular electron correlation. The calculations also show that the formation entropy destabilizes both complexes since from the two constituent molecules one complex molecule arises. The MP2/6-31G* procedure showed to be a suitable tool for the estimation of the relative importance of 1: 2 complexation compared to the 1: 1 complexation. In the gas phase the ratio of the equilibrium constants of both complexes K _1:2/K _1:1 = 0.09 was calculated. The presence of solvent, treated by the PCM, further destabilized the 1: 2 complex with respect to the 1: 1 complex. The ratio K _1:2/K _1:1 in CH₂Cl₂ calculated by the PCM method was 0.022, i.e. the 1: 2 complex was almost 50 times less stable than the 1: 1 complex, which is in agreement with available experimental data. According to the calculations, solvent always destabilizes complex with respect to the isolated (solvated) components.It was also found that charge polarization in the 1: 2 complex with respect to that in the 1: 1 complex was not strictly additive due to the presence of the second benzene molecule in the 1: 2 complex. Non-additive were also formation enthalpy, entropy, polarizability, charge transfer from donors to acceptor molecule and other properties. This fact is caused by a slightly changed interaction between constituent molecules in the 1: 2 complex in comparison with the 1: 1 complex as well as by the interaction between benzene molecules in the 1: 2 complex which is missing in the 1: 1 complex.Preliminary CIS/6-31G* theoretical study regarding a few first-electron (electron charge transfer) transitions in both complexes indicates the presence of Frenkel excitn and Davydov transition energy splitting in the 1: 2 “supercomplex” with the first allowed π → π* absorption transition at λ = 355 nm, while the first allowed transition in the case of 1: 1 complex was characterized by λ = 392 nm with the oscillator strength only half of that of the 1: 2 complex, which is in agreement with experiment. These unexpected large hypso-and hypochromic effects predicted by the theory could allow to overcome difficulties of the experimental determination of the 1: 2 complexation.     

Tellurium and selenium derivatives of π-cyclopentadienyliron dicarbonyl

Reactions of the diphenyl dichalcogenides Ph₂E₂ (E = Te, Se) with [π-CpFe-(CO)₂]₂ have been studied and several new complexes have been isolated and characterized. These include mononuclear π-CpFe(CO)₂EPh (E = Te, Se) and dinuclear [π-CpFe(CO)EPh]₂ (E = Te, Se). In the case of the dinuclear compounds two isomers were obtained and separated for selenium and a mixture of two isomers was obtained for tellurium. Comparisons of the donor properties of sulfur, selenium, and tellurium in these complexes are made.     

Electronic structure and aromaticity of planar singlet π-electron monocyclic π2 carbenes

Induced -electron ring currents and relative diamagnetic susceptibilities of planar singlet -electron monocyclic ² carbenes are calculated in the coupled variant of perturbation theory in the CNO method. It is shown that the parity theorem holds for charged planar ² and ² carbenes formally generated by the detachment of a proton or a hydride ion from alternant hydrocarbons. This leads, in such carbenes, to the same energies of singlet-singlet and singlet-triplet transitions, electric polarizabilities, conjugation energies, -electron ring currents, diamagnetic susceptibilities and current contributions to chemical shifts, whereas the charge contributions to the latter are of opposite signs.Donbas State Academy of Building and Architecture, 1 Derzhavina St., 339023 Makeevka, Donetsk Region, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 157–162, May–June, 1996. Original article submitted December 5, 1994.     

The Mechanism of the Initial Dark Oxidation of Ethers and the Ether-Oxygen Contact Charge Transfer Complex

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Synthesis and properties of thiophene-functionalized π-extended tetrathiafulvalenes

Two molecular ensembles composed of an array of thiophene-extended tetrathiafulvalene-thiophene were synthesized using Stille coupling and Horner-Wittig reaction as the key steps. Electrochemical redox and electronic absorption properties were investigated by voltammetric and UV-vis spectroscopic analyses.     

Excited-State Dynamics of Non-Luminescent and Luminescent π-Radicals

Recently, the potential use of organic π-radicals and related spin systems has been expanded to modern technological applications. The unique excited-state dynamics of organic π-radicals can be useful to improve the stability of photochemically unstable organic compounds, make the polarization transfer applicable to information technology, and achieve effective up-conversion of interest for luminescence bioimaging, among others. Furthermore, highly luminescent stable π-radicals have been recently reported, which are especially interesting for application in organic light-emitting devices owing to their potential to provide an internal quantum efficiency of 100 %. Thus, the excited-state nature of stable π-radicals as well as the control of their excited-state spin dynamics are emerging topics both in terms of fundamental science and related technological applications. In this minireview, we focus on the excited-state dynamics of both photostable non(weakly)-luminescent and luminescent π-radicals, which are opposites of each other. In particular, we cover the following topics: 1) effective generation of high-spin photoexcited states and control of the excited-state dynamics by using non-luminescent π-radicals, 2) unique excited-state dynamics of luminescent π-radicals and radical excimers, and 3) applications utilizing excited-state dynamics of π-radicals.     

Titanylation and vanadylation of highly π-conjugated porphyrins

We report the efficient synthesis of tetrabicycloporphyrin titanyl and vanadyl without decomposition of the bicyclo[2.2.2]octadiene unit. The complexes were heated under vacuum to give titanyl and vanadyl tetrabenzoporphyrins in 100% yield. We also titanylated and vanadylated tetra[2,3]naphthoporphyrin and tetra[2,3]anthraporphyrin, which have a greater degree of π conjugation than tetrabenzoporphyrin.     

Synthesis and Crystal Structure of Nickel Complex of DSEN

1INTRoDUCTIoNTheSchiffbasesareofgreatimportanceincoordinationchemistryasligands.TransitionmetalcomplexespreparedfromsalicylaldehydeSchiffbasespossessbiologi-calactivities[1~33.Forexample,Mn,Fe,Co,Ni,ZnandMoionsinproteincarryoxygen,transmitelectronandstoreprotein.Furthermore,manyofthiskindofcomplexescanalsobeusedashomogeneouscatalysts['~5i.WehavereportedthatSchiffbasespreparedbysalicylaldehydeandtriazolehavecatalyticactivitiesforsyn-thesizingethylenecarbonatet6).Forfurtherstudiesoftheca…     

The role of vibronic interactions on intramolecular and intermolecular electron transfer in π-conjugated oligomers

The importance of electron-vibrational coupling for intermolecular and intramolecular electron-transfer processes is discussed on the basis of first-principles correlated quantum-mechanical calculations and of a dynamic vibronic approach. The methodology is illustrated for examples selected from some of our recent work. In all instances, the theoretical results are thoroughly compared to experimental data.     

The Potential of π-Bonded Organometallic Polymers in Catalyst Design

Reductive substitution, the process whereby a hydrocarbon ligand, usually a cyclopentadienyl group, in a transition metal complex is replaced by another unsaturated hydrocarbon with concomitant metal reduction has been utilized to prepare novel complexes of Cr°, Cr^I, Mn^I, Co^I and Ni°. Similarly, ligand substitution, defined more generally as replacement of ligand(s) of a metal complex by an unsaturated hydrocarbon but with no change in the oxidation state of the metal, has resulted in the synthesis of a series of tetraphenylborate and substituted tetraphenylborate complexes of Fe^II, Mo^I, Cr^I, W^I, and Co^I. These procedures and the complexes derived therefrom are considered models for polymers incorporating a variety of novel features.