Electron Spin Resonance:  A Major Probe for Molecular Conductors

Coulon, C.; Clérac, Rodolphe

doi:10.1021/cr030639w

Cited by 62 publications

(50 citation statements)

References 489 publications

(862 reference statements)

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“…A single Lorentzian signal was observed down to 50 K, below which the EPR spectra of each crystal differed owing to the effect of defect spin. Therefore, we will discuss EPR data above 50 K. The angle dependence of g-values indicated that the signal was solely ascribed to TCNQ À (g ¼ 2:0025{2:0030 (==ab) and 2.0024-2.0028 (==ac), which agreed with the reported g-values for TCNQ À (g min ¼ 2:0020 and g max ¼ 2:0032) 34 ). The constant g-value against temperature indicated that there was no orientation change of TCNQ À (Fig.…”

Section: S CMsupporting

confidence: 84%

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Murata¹,

Saito²,

Nishimura³

et al. 2008

Bulletin of the Chemical Society of Japan

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Reaction between cytosine, a nucleobase, in methanol and several 7,7,8,8-tetracyanoquinodimethane derivatives (R-TCNQ) in acetonitrile yielded three kinds of ionic solids; (I) insulators composed of methoxy-substituted R-TCNQ anions, (II) semiconducting fully ionic R-TCNQ radical anion salts, and (III) conductive partially ionic or mixed-valent R-TCNQ radical anion salts. Electronic and chemical structures of these products were characterized by optical and magnetic measurements, and structural and elemental analyses. Cation units in all products were found to be protonated cytosine species. Crystal structures were determined for methoxy-substituted anion salts (R = F 4 and H) in Group I and R-TCNQ radical anion salts (R = H and Et 2 ) in Group II with hemiprotonated cytosine pairs formed by triple self-complementary hydrogen bonds. They established one-dimensional hemiprotonated cytosine ribbons by double complementary hydrogen bonds. Hydrogen bonds between cytosine and R-TCNQ anions exhibited high potential to regulate molecular arrangements producing a segregated layered structure and uniform arrangement of R-TCNQ radical anion columns stable down to low temperature. The partially ionic salt of MeTCNQ in Group III exhibited metallic behavior and the highest conductivity of 10 þ1 S cm À1 so far observed for charge-transfer complexes based on biological molecules.Biological molecules such as proteins, enzymes, DNA, etc., establish well-defined and complicated self-assembling structures which are important factors in the exhibition of their biological functions. This feature of biological molecules has attracted much attention from the viewpoint of supramolecular chemistry and crystal engineering in recent study of molecule-based materials.2 In research for organic conductors, several attempts to investigate charge-transfer (CT) complexes based on a variety of biological molecules have been also undertaken.

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Section: S CMsupporting

confidence: 84%

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Murata¹,

Saito²,

Nishimura³

et al. 2008

Bulletin of the Chemical Society of Japan

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“…27 This technique has been employed in the study of various organic materials including charge-transfer salts, 28,29 doped fullerenes, 30 and radicals. 31,32 In a typical single crystal experiment, microwave radiation is applied to a sample at a set frequency, and the energies of magnetic excitations are tuned using an external field H ext that can be varied in magnitude and direction with respect to the crystal.…”

Section: Fmr Studiesmentioning

confidence: 99%

Spin-orbit effects in heavy-atom organic radical ferromagnets

et al. 2012

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We discuss the effects of the spin-orbit interaction on heavy atom organic magnets with specific reference to a series of isostructural sulfur-and selenium-based radical ferromagnets of tetragonal space group P42 1 m. Using a perturbative approach, we show the spin-orbit effects lead to a pairwise anisotropic exchange interaction between neighboring radicals that provides an easy magnetic axis running parallel to the c-axis. Estimates of the magnitude of this magnetic anisotropy explain the significant increase in the coercive fields by virtue of selenium incorporation. Complementing this theoretical discussion are the results of ferromagnetic resonance studies, which provide an experimental verification of both the magnitude and symmetry of the spin-orbit terms. Taken as a whole, the results underscore the importance of heavy atoms and crystal symmetry in the design of molecular ferromagnets with large magnetic anisotropy and high ordering temperatures.

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“…The electrons are sufficiently delocalized on the EPR timescale ( % 10 À10 s) for both the electron-nuclear hyperfine interactions and the dipolar interactions between nearby spins to be averaged out. The electronic (including EPR) and magnetic behavior of such systems has been investigated extensively for several decades [18] and the behavior of the present system is most readily elucidated in qualitative terms by reference to earlier works on similar complexes rather than by attempting a quantitative ab initio interpretation.…”

Section: Epr Magnetism and Conductivitymentioning

confidence: 99%

Two‐Step Electrochemically Directed Synthesis of Pr₄N(TCNQ)_n(n=1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain

Boas

et al. 2011

Chemistry A European J

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Solid-state electrochemistry of a tetracyanoquinodimethane (TCNQ)-modified electrode in contact with a tetrapropylammonium cation (Pr(4)N(+)) electrolyte showed two electron-transfer steps to give Pr(4)N(TCNQ)(2) (1) and Pr(4)N(TCNQ) (2) rather than the traditional one-electron step to directly give Pr(4)N(TCNQ). Two thermodynamically stable Pr(4)N(+)-TCNQ stoichiometries, 1 and 2, were synthesized and characterized. The degree of charge transfer (ρ) calculated from the crystal structure is -0.5 for the TCNQ moieties in 1 and -1.0 for those in 2. Raman spectra for Pr(4)N(TCNQ)(2) show only one resonance for the extracyclic C=C stretching at 1423 cm(-1), which lies approximately midway between that of TCNQ at 1454 cm(-1) and TCNQ(-) at 1380 cm(-1). Both the magnetic susceptibility and EPR spectra are temperature-dependent, with a magnetic moment close to that for one unpaired electron per (TCNQ)(2) unit in 1, whereas 2 is almost diamagnetic. Pressed discs of both complexes show conductivity (1-2×10(-5) S cm(-1)) in the semiconductor range. For 1, the position of zero current for the steady-state voltammograms implies 50% of TCNQ(-) and 50% TCNQ(0) is present in solution, thereby supporting a dissociation of (TCNQ)(2)(-) in solution, but is indicative of only TCNQ(-) being present for 2.

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Electron Spin Resonance: A Major Probe for Molecular Conductors

Cited by 62 publications

References 489 publications

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Spin-orbit effects in heavy-atom organic radical ferromagnets

Two‐Step Electrochemically Directed Synthesis of Pr₄N(TCNQ)_n(n=1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain

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Electron Spin Resonance: A Major Probe for Molecular Conductors

Cited by 62 publications

References 489 publications

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Spin-orbit effects in heavy-atom organic radical ferromagnets

Two‐Step Electrochemically Directed Synthesis of Pr4N(TCNQ)n(n=1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain

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Two‐Step Electrochemically Directed Synthesis of Pr₄N(TCNQ)_n(n=1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain