Magnetic Resonance in Ion-Radical Organic Solids

Soos, Z. G.; Bondeson, S. R.

doi:10.1007/978-1-4684-4175-8_4

Cited by 13 publications

(6 citation statements)

References 312 publications

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“…The design of new organic ion radicals is a subject of current interest since these structural units are responsible for the unusual optical (NIR), magnetic, and electrical properties of the mixed-valence compounds 3 and some conducting polymers . However, very few organic mixed-valence compounds are known, most of them being formed from an electrically neutral, nonradical species by a single-electron addition or removal ( nondistonic ) .…”

Section: Introductionmentioning

confidence: 99%

Inert Carbon Free Radicals. 14. Synthesis, Isolation, and Properties of Two Strongly π−π Interacting Mixed-Valence Compounds: The Perchloro-4,4‘-ethynylenebis(triphenylmethyl) Anion Radical Potassium (18-Crown-6) Salt and the Perchloro-α,α,α‘,α‘-tetraphenyl-p-xylylene Anion Radical Tetrabutylammonium Salt

Domingo¹,

Castañer²,

Riera³

et al. 1997

Chem. Mater.

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The perchloro-4,4′-ethynylenebis(triphenylmethyl) anion radical (11) potassium 18-crown-6 salt and perchloro-R,R,R′,R′-tetraphenyl-p-xylylene anion radical (15) tetrabutylammonium salt have been isolated in pure form as solids perfectly stable in the air and moisture, withstanding temperatures up to 200 °C. Their physical and chemical properties have been studied using UV-vis, NIR, IR, ESR, cyclic voltammetry, magnetic susceptibility, and electrical conductivity and compared with other already reported and structurally related perchlorotriphenylmethyl systems in which an intramolecular "spin-charge exchange" takes place. In contrast with those compounds, the acetylene anion radical 11 shows an unusual band in the vis-NIR region (754 nm, 37.7 kcal/mol), not present in its corresponding biradical 10 and dianion 9, and the Thiele anion radical 15 shows a typical, but bathochromically shifted ca. 10 kcal/mol, radical band and an unusual NIR band at 1342 nm (21.2 kcal/mol) of high intensity. Application of Hush's theory of mixed-valence class III compounds to these unusual bands for PTM compounds, gives the values of ca. 18 and 10 kcal/mol for the resonance energy of 11 and 15 respectively. The close coincidence of these theoretical values with those obtained by comparing the UV-vis spectra of 11 and 15 with the PTM anion radical systems without resonance interaction can be regarded as a preliminary test of the validity of Hush's theory of organic mixed-valence class III compounds. The cyclic voltammograms of anion radicals 11 and 15 indicate that their precursors, the biradical 10 and perchloro-Thiele hydrocarbon 16 have suitable redox potentials as acceptor components of electrically conducting charge-transfer complexes. 11 and 15 present magnetic properties similar to those of PTM radicals, but as a consequence of the "spin charge resonance" they show a halving of the hyperfine coupling constants. More spectacular differences are shown in the electrical conductivity of 11 and 15 with values of 10 -4 and 10 -6 S cm -1 , respectively, which can be a consequence of their molecular design as suggested the ∆E 1/2 differences (6.4 vs 12 kcal/mol). These conductivity values are in the range of the corresponding TCNQ salts.

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Section: Introductionmentioning

confidence: 99%

Inert Carbon Free Radicals. 14. Synthesis, Isolation, and Properties of Two Strongly π−π Interacting Mixed-Valence Compounds: The Perchloro-4,4‘-ethynylenebis(triphenylmethyl) Anion Radical Potassium (18-Crown-6) Salt and the Perchloro-α,α,α‘,α‘-tetraphenyl-p-xylylene Anion Radical Tetrabutylammonium Salt

Domingo¹,

Castañer²,

Riera³

et al. 1997

Chem. Mater.

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“…For the presented series of neutral π-radical dimers the approximate 2| t| / U values are shown in Table . U was estimated by the equation , U = S 0 + S 2 − 2 T where S 0 , S 2 , and T are the energies of the ground state, the second excited singlet, and excited triplet state, respectively. Note that the SOMO−SOMO splittings depend considerably on the intermolecular packing.…”

mentioning

confidence: 99%

Is There a Lower Limit to the CC Bonding Distances in Neutral Radical π-Dimers? The Case of Phenalenyl Derivatives

Tian

Kertész

2010

J. Am. Chem. Soc.

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Two-electron multicenter (2e/mc) bonding of phenalenyl (PHYL) pi-dimers was found to be significantly affected by the electron density on the bonding active sites. The computational analysis shows that, upon appropriate beta-substitutions, the newly introduced dimers have the shortest and strongest covalent bonding interactions seen in any neutral pi-dimer. The unusual strengthening of the bonding was attributed to the reduced lone pair bond weakening effect, LPBWE, upon substitutions with electron-withdrawing groups.

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“…Frenkel excitons present in a high concentration can through a fast exchange give rise to only one single exchange narrowed ESR line, but, in this case the linewidth increases with decreasing temperature [18,20]. Thus, the temperature dependence of both AB,, and x shows that the triplet states are of the Wannier type.…”

Section: The Esr Linewidthmentioning

confidence: 84%

Electronic Properties and Crystal Structure of a Methylthio Substituted Naphthalene Cation Radical Salt: (DMbTN)₃(ClO₄)₂

Söderholm

Hellberg

Krzystek

et al. 1990

Physica Status Solidi (b)

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The crystal structure, the conductivity, and the magnetic properties of the monoclinic cation radical salt 2,7-dimethoxy-3,6-bis(methylthio)naphthalene-perchlorate [(DMbTN),(C10,),] are presented. The stack of DMbTN molecules consists of triads which make the salt semiconducting, 4 3 0 0 K) z S/cm, with a band gap of 0.6 eV. In spite of the low conductivity the susceptibility is very high, about 0.27 spins/complex. This is due to the presence of significant correlation effects, causing the coupling between the spins to be antiferromagnetic with J = 56 meV. Because of the trimerization of the DMbTN stack the primary spin excitations are thermally activated triplet spin excitations of the Wannier type. The electrical and magnetic properties for T 5 200 K are governed by the presence of deep defect levels in the band gap. The ESR linewidth is unusually narrow, about 1 G at 300 K, for an ion-radical salt containing sulphur, this implies that the spin density on the sulphur atoms is very low.

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Magnetic Resonance in Ion-Radical Organic Solids

Cited by 13 publications

References 312 publications

Is There a Lower Limit to the CC Bonding Distances in Neutral Radical π-Dimers? The Case of Phenalenyl Derivatives

Electronic Properties and Crystal Structure of a Methylthio Substituted Naphthalene Cation Radical Salt: (DMbTN)₃(ClO₄)₂

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Magnetic Resonance in Ion-Radical Organic Solids

Cited by 13 publications

References 312 publications

Is There a Lower Limit to the CC Bonding Distances in Neutral Radical π-Dimers? The Case of Phenalenyl Derivatives

Electronic Properties and Crystal Structure of a Methylthio Substituted Naphthalene Cation Radical Salt: (DMbTN)3(ClO4)2

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Electronic Properties and Crystal Structure of a Methylthio Substituted Naphthalene Cation Radical Salt: (DMbTN)₃(ClO₄)₂