Raman scattering in ferromagnetic TDAE-C60 compared to TDAE-C70

Денисов, В. Н.; Zakhidov, A.A.; Ruani, G.; Zamboni, R.; Taliani, C.; Tanaka, Kazuyoshi; Yoshizawa, Kazunari; Okahara, T.; Yamabe, Tokio; Achiba, Yohji

doi:10.1016/0379-6779(93)90078-b

Cited by 19 publications

(18 citation statements)

References 11 publications

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“…As an adsorbate on a metal surface, the electronegative C 60 molecule naturally picks up electrons [23,24], and recent evidence has been provided of charge transfer which can be as large as n=6 [17]. In the solid state, finally, there are compounds, covering a wide range of charge transfers, from n=1, as in TDAE + -C − 60 [25] or Rb 1 C 60 [26], n=3, as in K 3 C 60 or Rb 3 C 60 [27], n=4 as in K 4 C 60 [28], n=6 as in Rb 6 C 60 [29], or even higher as in Li 12 C 60 [30,16].…”

Section: The Hamiltonian Includes the Termsmentioning

confidence: 99%

Electron-vibron interactions in charged fullerenes. II. Pair energies and spectra

1994

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The ground state energy shifts and excitation spectra of charged buckminsterfullerene C n− 60 , n = 1, . . . 5 are calculated. The electronvibron Hamiltonian of Part I is extended to include all A g and H g modes with experimentally determined frequencies and theoretically estimated coupling constants. Complex splitting patterns of H g vibrational levels are found. Our results are relevant to EPR measurements of spin splittings in C 2− 60 and C 3− 60 in solution. Spectroscopic gas-phase experiments will be of interest for further testing of this theory. As found in Part I, degeneracies in the electron and vibron Hamiltonians give rise to a dynamical Jahn Teller effect, and to a considerable * Email: manini@tsmi19.sissa.it † Email: tosatti@tsmi19.sissa.it ‡ Email: assa@phassa.technion.ac.il 1 enhancement of the electronic pairing interaction. This helps to overcome repulsive Coulomb interactions and has important implications for superconductivity in K 3 C 60 and the insulating state in K 4 C 60 .

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Section: The Hamiltonian Includes the Termsmentioning

confidence: 99%

Electron-vibron interactions in charged fullerenes. II. Pair energies and spectra

1994

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“…Comparing the effects of resonance on our results with the data of [8] who performed Raman spectroscopy at λ=1064 nm we see that positions of the tangential modes (w>700 cm -1 ) correspond well in the two cases, but there are big differences in the frequencies of the radial modes. According to [8] all radial modes are downshifted near 7 cm -1 , which is not observed with 514.5 nm excitation.…”

Section: Resultsmentioning

confidence: 50%

“…According to [8] all radial modes are downshifted near 7 cm -1 , which is not observed with 514.5 nm excitation. We suggest that the origin of this effect is related to resonance of the 1064 nm laser line with the t1u→t1g electronic transition of C60 -anion [15].…”

Section: Resultsmentioning

confidence: 88%

“…It should be noted that Raman modes with mainly radial character of carbon displacements Ag(1), Hg(1,2,3) [13] are downshifted in frequency much less (or not shifted at all) than the high frequency modes Ag(2), Hg (7,8) with predominantly tangential character. The analogous behavior of the Raman modes observed earlier in the spectra of alkali metal doped C60 compounds was explained by a charge transfer-related effect [14].…”

Section: Resultsmentioning

confidence: 99%

“…The early Raman and IR measurements of TDAE-C60 were performed on powder samples or doped C60 films [7][8][9] and their results are rather controversial. Thus, the experiments performed on TDAE-C60 single crystals are of great importance.…”

Section: Introductionmentioning

confidence: 99%

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Low temperature raman spectra on tdae-c60 single crystals

et al. 1997

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Low-temperature single crystal Raman spectra are presented for the organic ferromagnetic insulator TDAE-C60. The mode intensities, lineshifts, linewidths and depolarization ratios are compared with alkali-doped fullerene materials and with pure C60. A comparison of visible laser light excited spectra (Eexc. = 2.41 eV) with infrared excited Raman measurements (Eexc. = 1.17 eV) shows a selective resonance effect whereby in the visible, a frequency shift of only the tangential modes is observed, while in the infraredwhich is resonant with the t1u → t1g electronic transition -also the radial modes are observed to shift. The effect is attributed to Raman resonance with different relaxed states of C60 anion.

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Synthesis and electrochemical properties of 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles and tricyanoacrylates

et al. 1995

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The reaction of phenylacetylenes 4a-h with copper(1) acetate (5) and TCNE (tetracyanoethylene) in THFIacetonitrile gave 4-phenyl-l-buten-3-yne-l,1,2-tricarbonitriles 6a-h. 4i did not react to give 6i. The phenylacetylenes 4b-i were prepared by a two-step synthesis starting from the corresponding phenyl halides lb-i. The tricyanoacrylates 8 were synthesized from the corresponding cyanoacetates ?, TCNE and catalytic amounts of pyridine in THE -Cyclovoltammetric investigations showed that the butenynes 6 and the tricyanoacrylates 8 are strong electron acceptors which can be easily reduced. The radical anions 6'-are unstable in acetonitrile and react irreversibly with 6 to give oligomeric anions 6;-. Only 4-(2,4,6-trimethoxyphenyl)-1 -buten-3-yne-1,1,2-tricarbonitrile (6h) is reduced to a radical anion 6h'-which associates with 6h in a reversible follow-up process to form a dimeric anion 6h;-. By contrast, the tricyanoacrylates 8 can be reversibly reduced to their respective radical anions and dianions.In the last three decades various theories of organic ferromagnets were proposed [']. Compounds with unpaired electrons like stable organic radicals or radical ions are always required. In recent years organic materials with ferromagnetic properties at low temperatures could be synthesized. These materials are ionic charge-transfer complexes (CT complexes) prepared from strong electron donors (D) and strong electron acceptors (A); Miller et a1.t21 synthesized an organometallic CT complex decamethylferrocene (D) and TCNE (tetracyanoethylene) (A) with a Curie temperature T, = 4.8 K. Wudl et al.L3] published in 1991 the first purely organic ferromagnet, a CT complex containing tetrakis(dimethy1amino)ethene (D) and f~l1erene-C~~ (A) with T, = 16.1 K.In our approach to ferromagnetic CT complexes we investigated the synthesis of new organic donors and acceptors as well as their electrochemical behaviour which gave information about redox potentials and stabilities of the corresponding radical ions.In this paper we describe the synthesis and the electrochemical properties of 4-phenyl-1 -buten-3-yne-1,1,2-tricarbonitriles 6 with functional groups at the phenyl ring and tricyanoacrylates 8. These compounds derive from TCNE by replacement of a cyano group by a phenylacetylene or an ester moiety. They are still unknown, except 6a which is described by Ukhin et al.t4] and by Hopf et al.L5], and methyl tricyanoacrylate which has been published by Hall et al.r61. We investigated butenynes 6 and tricyanoacrylates 8 because we expected them to be strong electron acceptors which possibly could form stable radical anions. Synthesis of Phenylacetylenes 4 and Butenynes 6The catalytic condensation of phenyl halides with protected acetylenes gives, after removal of the protecting group, the corresponding phenylacetylene~[~-~]. We found that these reactions are suitable for the preparation of phenylacetylenes 4b-i. The protected acetylenes used were 2-methyl-3-butyn-2-01 (Scheme 1) and 2-propyn-1-01 (Scheme 2). During the condensations under...

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Raman scattering in ferromagnetic TDAE-C60 compared to TDAE-C70

Cited by 19 publications

References 11 publications

Electron-vibron interactions in charged fullerenes. II. Pair energies and spectra

Electron-vibron interactions in charged fullerenes. II. Pair energies and spectra

Low temperature raman spectra on tdae-c60 single crystals

Synthesis and electrochemical properties of 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles and tricyanoacrylates

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