Tetracyanoethylene Anion Radical Research Articles

Electronic and Vibrational Manifold of Tetracyanoethylene-Chloronaphthalene Charge Transfer Complex in Solution: Insights from TD-DFT and Ab Initio Molecular Dynamics.

The interplay between light absorption and the molecular environment has a central role in the observed photophysics of a wide range of photoinduced chemical and biological phenomena. The understanding of the interplay between vibrational and electronic transitions is the focus of this work, since it can provide a rationale to tune the optical properties of charge transfer (CT) materials used for technological applications. A clear description of these processes poses a nontrivial challenge from both the theoretical and experimental points of view, where the main issue is how to accurately describe and probe drastic changes in the electronic structure and the ultrafast molecular relaxation and dynamics. In this work we focused on the intermolecular CT reaction that occurs upon photon absorption in a π-stacked model system in dichloromethane solution, in which the 1-chloronaphthalene (1ClN) acts as the electron donor and tetracyanoethylene (TCNE) is the electron acceptor. Density functional theory calculations have been carried out to characterize both the ground-state properties and more importantly the low-lying CT electronic transition, and excellent agreement with recently available experimental results [MathiesR. A.; et al. J. Phys. Chem. A2018, 122 ( (14), ), 359429558802] was obtained. The minima of the ground state and first singlet excited state have been accurately characterized in terms of spatial arrangements and vibrational Raman frequencies, and the CT natures of the first two low-lying electronic transitions in the absorption spectra have been addressed and clarified too. Finally, by modeling the possible coordination sites of the TCNE electron acceptor with respect to monovalent ions (Na+, K+) in an implicit solution of acetonitrile, we find that TCNE can accommodate a counterion in two different arrangements, parallel and orthogonal to the C=C axis, leading to the formation of a contact ion pair. The nature of the counterion and its relative position entail structural modifications of the TCNE radical anion, mainly the central C=C and C≡N bonds, compared to the isolated case. An important red shift of the C=C stretching frequency was observed when the counterion is orthogonal to the double bond, to a greater extent for Na+. On the contrary, in the second case, where the counterion ion lies along the internuclear C=C axis, we find that K+ polarizes the electron density of the double bond more, resulting in a greater red shift than with Na+.

Polynomial coefficients. Application to spin-spin splitting by N equivalent nuclei of spin I > 1/2

The NMR intensity pattern of a nucleus split by N identical nuclei of spin 1/2 is given by the familiar binomial coefficients. These are conveniently obtained from Pascal's Triangle, equivalent to the chemist's branching diagram. Much less well known is the pattern from splitting by N identical nuclei of spin I > 1/2. This had been presented originally in terms of multinomial coefficients, but polynomial coefficients are more convenient. These describe the number of ways that N objects can be distributed to 2I+1 numbered boxes. They arise in the polynomial expansion, which is well known to mathematicians but not to chemists and which is conveniently obtained from generalizations of Pascal's Triangle. Examples include the 13C NMR of methanol-d3 and the EPR of tetracyanoethylene radical anion. Predictions are made for the 1H NMR of HC(CD3)3 and the 31P{1H} NMR of (CD3CH2)4P+.

Microwave Spin Frequency Comb Memory Protocol Controlled by Gradient Magnetic Pulses

We have demonstrated a combination of frequency comb spin-echo protocol in a conventional microwave pulsed electron spin resonance spectrometer with gradient pulses of the external magnetic field applied for on-demand retrieval of signal microwave pulses at the required moments of time. A natural high-finesse periodic structure was used as a carrier of stored information. The structure is made out of hyperfine lines of electron spin resonance of tetracyanoethylene anion radicals in toluene at room temperature. Herein, we have also observed that using the pulses of gradient magnetic field can increase the memory capacity. The experimental results demonstrated promising opportunities for controlling electron nuclear spin coherence, which could be useful for implementation of broadband microwave or optical-microwave noise free quantum memory protocols.

Room-temperature storage of electromagnetic pulses on a high-finesse natural spin-frequency comb

We have demonstrated the storage of electromagnetic pulses by exploiting a spin-echo quantum memory protocol. Therein, we have used an electron-nuclear spin ensemble of tetracyanoethylene anion radicals in toluene which has a natural periodic structure of narrow electron-spin resonance (ESR) hyperfine lines. Robust storage up to three temporal modes has been achieved with storage time $\ensuremath{\sim}1$ $\ensuremath{\mu}\mathrm{s}$ at room temperature on a conventional pulsed ESR spectrometer. On-demand retrieval of the stored field has been realized by holding the electron spins in a dephased state during the storage time. A longer storage time and the highest overall finesse $\ensuremath{\sim}20$ of the ESR spectrum have been attained by using multipulse dynamical decoupling of the electron spins from the noisy environment. The obtained experimental results suggest that the electron-nuclear spin ensemble of radicals in liquid should be a promising system for the room-temperature quantum memory.

Tuning the Electronic Structure of Graphene by an Organic Molecule

The electronic structure of an electron-acceptor molecule, tetracyanoethylene (TCNE), on graphene was investigated using the first-principles method based on density functional theory. It was theoretically demonstrated that a p-type graphene can be obtained via charge transfer between an organic molecule and graphene. Both the carrier concentration and band gap at the Dirac point can be controlled by coverage of organic molecules. The spin split and partially filled pi* orbitals of the TCNE anion radical induce spin density in the graphene layer. Surface modification of graphene by organic molecules could be a simple and effective method to control the electronic structure of graphene over a wide range.

Synthesis, structure and magnetic properties of a geminal μ 2-tetracyanoethylene radical anion bridged coordination polymer

A tetracyanoethylene (TCNE) bridged coordination polymer, [Mn(cyclen)(μ 2-TCNE)] · TCNE ( 1), (cyclen = 1,4,7,10-tetraazacyclododecane, TCNE = tetracyanoethylene), has been synthesized by combining [Mn II(cyclen)] 2+ and the potassium salt of TCNE radical anion, K[TCNE]. The compound crystallizes in two polymorphs. Both structures feature formal TCNE radical anion ligands in an unusual geminal (or 1,1−) bridging geometry between two high spin Mn(II) centers. The N TCNE–Mn–N TCNE bond angles of two bridging TCNE /− ligands are 88.07(9)° 1a and 85.44(14)° 1b, respectively. Each bridging TCNE /− is π stacked with an uncoordinated TCNE /− to form what can be construed as a diamagnetic dianion, TCNE 2 2 - , containing a 4-center 2-electron (4c/2e −) bond. The results of variable-temperature magnetic susceptibility measurements indicate behavior consistent with weak antiferromagnetic coupling between two Mn(II) centers with no significant contribution of spin from the organic radicals.

Synthetic, Structural, and Electrochemical Studies of Edge-Bridged Open Ferrocenes

The syntheses of the new compounds Fe(3-Me3Si-6,6-dmch)2, 2, and Fe[3-(i-Pr)3Si-6,6-dmch]2, 3, are reported, along with X-ray structural studies of these species, and of the previously reported Fe(1,3,5,6-temch)2 (dmch = dimethylcyclohexadienyl; temch = tetramethylcyclohexadienyl). Each species crystallized in something close to the expected gauche-eclipsed conformation. In accord with previous work on Fe(6,6-dmch)2, but in contrast to results for open ferrocenes such as Fe(2,4-C7H11)2 (C7H11 = dimethylpentadienyl), the three species under study undergo reversible one-electron oxidations at room temperature to stable 17-electron cations, with potentials for oxidation being more favorable than that for ferrocene by 0.51–0.78 V. The edge-bridged open ferrocenes also react in a 1:1 ratio with TCNE (TCNE = tetracyanoethylene), yielding salts that were shown spectroscopically to contain the expected cationic 17-electron metal complexes and the TCNE radical anion.

Organic- and molecule-based magnets

The discovery of organic- and molecule-based magnets has led to design and synthesis of several families with magnetic ordering temperatures as high as ∼125°C. Examples of soft and hard magnets with coercivities as high as 27 kOe have also been reported. Examples from our laboratory of organic-based magnets using the tetracyanoethylene radical anion, [TCNE]•−, are discussed. In addition, several molecule-based magnets based on Prussian Blue structured materials as well as dicyanamide are discussed.

Steric Influence on the Structure, Magnetic Properties, and Reactivity of Hexa- and Octaisopropylmanganocene

The reaction of KCpni (Cpni = (C3H7)nC5H5-n; n = 3, 4) with MnCl2 in THF produces the metallocenes (Cp3i)2Mn or (Cp4i)2Mn in good yield. Solid-state magnetic susceptibility measurements indicate that orange-red (Cp3i)2Mn is in high-spin/low-spin equilibrium at room temperature. In the solid-state, it has a centrosymmetric sandwich structure with an average Mn−C bond length (2.130(6) Å) typical of low-spin manganocenes. (Cp3i)2Mn reduces tetracyanoethylene (TCNE) to generate the TCNE radical anion. Despite the presence of additional electron-donating isopropyl groups, pale yellow (Cp4i)2Mn is entirely high-spin from room temperature to 10 K. The crystal structure of (Cp4i)2Mn reveals a bent metallocene structure, with a centroid−Mn−centroid angle of 167.4° and an average Mn−C distance of 2.42(2) Å. This structure is consistent with its high-spin electron configuration; the longer Mn−C bonds provide relief from the steric strain that would be present in a low-spin complex. The reaction of (Cp4i)2Mn with TCNE produces a tricyanovinylation product, C5(i-Pr)4HC(CN)C(CN)2, which was characterized by X-ray diffraction.

Molecular associations between indolizines and tetracyanoethylene

AbstractSpectroscopic, thermodynamic and kinetic properties of molecular interactions between indolizines and tetracyanoethylene are reported. The interactions involved in the complexes are weak as evidenced by the low formation constants. The kinetic behaviour indicates the initial formation of a pI‐complex that is rapidly transformed into a σ‐complex and thereafter into the final adduct(s). Apart from the results obtained by other techniques, infrared data clearly evidence vibrational contributes characteristic of the complexes, the tricyanovinyl derivatives and the tetracyanoethylene radical anion.

The Spin Density Distribution in the Tetracyanoethylene Radical Anion, [TCNE]˙−, by Single‐Crystal Polarized Neutron Diffraction

Not completely localized on the sp2-carbon atoms but distributed across the radical is the unpaired electron in the [TCNE]˙− radical anion. This was determined by the single-crystal polarized neutron diffraction study of Bu4N+ [TCNE]˙−. The experi mental results were in accord with quantum chemical calculations. The spin distribution within [TCNE]˙− according to the experiment is sp2-C:sp-C:N = 33: − 5:13.

Cover Picture (Angew. Chem. Int. Ed. Engl. 13/1994)

Angewandte Chemie International Edition in EnglishVolume 33, Issue 13 Cover PictureFree Access Cover Picture (Angew. Chem. Int. Ed. Engl. 13/1994) First published: July 18, 1994 https://doi.org/10.1002/anie.199413071Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract The cover picture shows the electron density distribution for the tetracyanoethylene radical anion as calculated with a hybird model using a minimal basis set of atomic orbitals (pz oritabls for C and N) and a multipolar expansion of the spin density. The picture shows the best agreement with the experimental data obtained by neutron diffraction. The significant electron density apparent at the nitrogen atoms is necessary for magnetic interactions. More on the analysis is given by J. S. Miller et al. on p. 139ff. Citing Literature Volume33, Issue13July 18, 1994 RelatedInformation

Characterization of MoOs-zeolite prepared from ammonium molybdate

Mo03 zeolite (MoC)3-NaY zeolite) catalyst was prepared by the thermal decomposition of ammonium molybdate adsorbed in the NaY zeolite in aqueous media. The catalyst prepared thus was characte- rized by scanning electron microscope (SEM), measuring surface area (BET), X-ray diffraction, chemical analysis, effect of CO on adsorbed SO;, and the e.s.r. technique. The electron-accepting and -donating properties were also studied by measuring the concentration ofthiophenazine cation radical (TPQD*) and tetracyanoethylene anion radical (TONE ) formed. Ten percent M0+6 of MoOs-NaY zeolite when activated at 450°Cn vacuum changed to Mo+5 ions. The formation of Mo+3 was observed during 802 reduction by CO at 450°C.

A Pressure Dependent Antiferromagnetism of AlPcF·(TCNE)xFilm

Magnetic properties of fluoro-aluminum phthalocyanine (AlPcF) film doped with tetracyanoethylene (TCNE) are studied by ESR. A strong pressure dependence is observed: At 760 Torr an antiferromagnetic transition takes place at 175±3 K, while, in vacuum, no magnetic transition is observed. DC conductivity does not have any pressure dependence. An X-ray diffraction study indicates that a pressure dependence of interlayer distance inside the film is a structural origin of the pressure dependence of the magnetism. A resonance mechanism of a charge transfer between AlPcF cation radical (AlPcF + ·) and TCNE anion radical (TCNE - ·) is proposed in order to explain an interchain magnetic coupling.

Paramagnetic relaxation of radical species in .gamma.-irradiated glassy ethanol solution of tetracyanoethylene anion radical: role of spectral diffusion in cross relaxation

Paramagnetic relaxation of radical species in .gamma.-irradiated glassy ethanol solution of tetracyanoethylene anion radical: role of spectral diffusion in cross relaxation

Mechano‐ions produced by mechanical fracture of solid polymers

AbstractIt is said that the free radical caused by C‐C‐bond scission, homogeneous scission, is produced by mechanical degradation. In addition to free radicals, ionic species are produced due to the mechanical destruction of the polymers. Studies in our group concerning this problem are summarized. When the polymers were ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document}) was detected by electron spin resonance (ESR) method. The TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document} is formed by the abstraction of electrons by TCNE from the anion produced by a heterogeneous bond scission of carboncarbon bonds in the polymer main chain. The identification of TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document} was carried out by the spectral simulation on the basis of an anisotropic hyperfine tensor including a forbidden transition term. Several polymers were examined; polyethylene, polypropylene, poly(tetrafluoroethylene) and poly(vinylidene fluoride). The ratio of ionic species and free radicals is discussed.

Ionic products in ground polymer. IV. Anions in poly(vinylidene fluoride)

AbstractWhen poly(vinylidene fluoride) (PVDF) was ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE‐) was detected in the mixture by ESR spectroscopy. The TCNE.‐ is formed by the abstraction of electrons by TCNE from the anion that is produced by a heterogeneous bond scission of carbon‐carbon bonds in the polymer main chain. The assignment of TCNE.‐ was carried out by the ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that includes a forbidden transition term. At least 85% of the bond scission of the PVDF main chain is induced by a heterogeneous process to produce ionic products. The yield of these mechanions seems to increase with the polarity of carbon‐carbon bond owing to a substituent group bonded to the carbon in the polymer main chain.

Ionic species produced by mechanical fracture of solid polymer. III. Anions from polytetrafluoroethylene

AbstractThe tetracyanoethylene anion radical (\documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document}) was detected by ESR spectroscopy in polytetrafluoroethylene (PTFE), which had been mechanically fractured in vacuo with tetracyanoethylene (TCNE) at 77 K. The assignment of \documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document} was carried out by ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that included a forbidden transition term. The \documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document} is formed by abstraction of an electron by TCNE from the anion that is produced by heterogeneous scission of the carbon‐carbon bond in the main chain of PTFE. At least 16% of the scission of the main chains of PTFE occurs by a heterogeneous process to produce the anions. Approximately 50% of the anions decay during annealing for 30 min at 220 K in the dark, and all anions decay within 15 min at 325 K.

Über die Reaktion von Chloranil mit Cyanidionen – eine ESR‐Studie

On the Reaction of Chloranil with Cyanide Ions – an ESR StudyThe reaction of chloranil 1 with cyanide ions in acetonitrile and methanol solutions has been studied. The ESR Spectra revealed the formation of semiquinone anion radicals 7,8, and 9. The latter has been found as its protonated form in methanol only. In addition, both 1 and 2,3‐dicyano‐5,6‐dichloro‐1,4‐benzoquinone 4 gave tetracyanoethylene anion radicals 6 upon reaction with cyanide ions in acetonitrile. Using 13C‐labelled cyanide 6 was shown to originate from the fragmentation of the cyanide addition product to 4. Using the spin trapping technique it was found that no cyanyl free radicals are formed during the thermal reaction of either 1 or 4 with cyanide ions.

Ionic products from the mechanical fracture of solid polypropylene

When polypropylene was fractured with tetracyanoethylene (TCNE) in the dark in vacuo at 77 K, the TCNE anion radical, TCNE — was detected (using e.s.r. methods). The TCNE — is produced by the attraction of an electron by TCNE from an anion arising from the mechanical fracture of solid polypropylene. This is presumably by ‘heterogeneous scission’ of main-chain carbon—carbon bonds in the polymer. Free radicals of the chain-end type arising from the mechanical fracture of solid polypropylene are also produced by ‘homogeneous scission’. At least 37% of scission occurs by the heterogeneous process.