The ground state of the coronene dinegative ion

Jesse, R.E.; Hoytink, G.J.

doi:10.1016/0009-2614(67)85036-x

Cited by 7 publications

(4 citation statements)

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“…The endocyclic bond angles range from 113.5° to 115.3° at C(1), C(2), C(4), and C(5), but at C(3) and C(6) are 128.9 °. There has been much theoretical discussion relating to the structure of the benzene dianion. , …”

Section: Resultsmentioning

confidence: 99%

Synthesis and Characterization of Organolanthanidocene(III) (Ln = La, Ce, Pr, Nd) Complexes Containing the 1,4-Cyclohexa-2,5-dienyl Ligand (Benzene 1,4-Dianion): Structures of [K([18]-crown-6)][Ln{η⁵-C₅H₃(SiMe₃)₂-1,3}₂(C₆H₆)] [Cp‘ ‘ = η⁵-C₅H₃(SiMe₃)₂-1,3; Ln = La, Ce, Nd]

et al. 1999

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The new tricyclopentadienyllanthanoid metal(III) complexes [LnCp‘ ‘3] are obtained in good yields from the appropriate anhydrous metal(III) triflate or chloride and 3/2 MgCp‘ ‘2 or 3 KCp‘ ‘ in tetrahydrofuran at ambient temperature [Cp‘ ‘ = η5-C5H3(SiMe3)2-1,3 and Ln = La (1) or Pr (3)]. Treatment of the appropriate compound 1 or 3, or [CeCp‘ ‘3] (2) or [NdCp‘ ‘3] (4), with 2 equiv of each ([18]-crown-6) and potassium in benzene at ambient temperature affords the red or red-brown (7) crystalline salts [K([18]-crown-6)][Ln{η5-C5H3(SiMe3)2-1,3}2(C6Η6)] [Ln = La (5), Ce (6), Pr (7), Nd (8)], with [K([18]crown-6)][Cp‘ ‘] as a coproduct. Each of 5−8 is soluble in hot benzene, which allowed the 1H NMR spectra to be recorded. The salt 5 is diamagnetic, consistent with its containing a lanthanate(III) anion. For 6−8, the 1H NMR spectral signals of the ([18]-crown-6) moiety are only slightly paramagnetically shifted. Hydrolysis of 5 (or 6−8) yields cyclohexa-1,4-diene. The molecular structures of the isomorphous salts 5, 6, and 8 reveal that each comprises a tight ion pair, a C6H6 ligand bridging the K and Ln atoms. The potassium atom has close contacts to the six crown ether oxygen atoms and the centroids of the 2,3- and 5,6-carbon atoms of the C6H6 ligand. The latter is boat-shaped, the shortest C−Ln distances being those to the 1- and 4-carbon atoms; the endocyclic bond angles at the 1- and 4-carbon atoms are narrower (110.65 ± 1.15°) than those at the other four (122.4 ± 1.2°), while the four C−C bonds to the 1- and 4-carbon atoms are longer (1.46 ± 0.02 Å) than the remaining two (1.350 ± 0.013 Å). The reaction of [LaCp‘ ‘3] (1) with K and ([18]-crown-6) in benzene, monitored by EPR spectroscopy, reveals the presence of at least four La(II) paramagnetic intermediate species prior to formation of 5.

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Section: Resultsmentioning

confidence: 99%

Synthesis and Characterization of Organolanthanidocene(III) (Ln = La, Ce, Pr, Nd) Complexes Containing the 1,4-Cyclohexa-2,5-dienyl Ligand (Benzene 1,4-Dianion): Structures of [K([18]-crown-6)][Ln{η⁵-C₅H₃(SiMe₃)₂-1,3}₂(C₆H₆)] [Cp‘ ‘ = η⁵-C₅H₃(SiMe₃)₂-1,3; Ln = La, Ce, Nd]

et al. 1999

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“…(1)-(3)], the Vt are the CI functions whose dominant terms are, respectively, (12) 1if;(E2a (13) lifi(A/) = 2-1/2 [1 Vtl1/ilifi21/i2I + I ifil1/ilVta1/ial], (14) and in the lowest triplet state the leading term is …”

Section: A Electronic Wavefunctions and Matrix Elementsmentioning

confidence: 99%

“…(12) and (13)J is identically zero, irrespective of the cation geometry, so that the only contributions come from the excited configurations. This contrasts with results for other Jahn-Teller systems,24.2S.20 and is due to the fact that coupling between the two components of ~(E2') is negligible compared to coupling with the 3048 cm-I higher ly.,(A I ').…”

Section: B Vibronic Wavefunctions and Energy Levelsmentioning

confidence: 99%

Effect of Vibronic Interaction on the Singlet-Triplet Separation in Cyclopentadienyl Cations

Purins

Feeley

1972

The Journal of Chemical Physics

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Vibronic wavefunctions and energies are obtained for the IAI', IE.', and 3A.' states of the cyclopentadienyl cation (C5H6+) and the pentadeuterio and pentachloro derivatives. Strong pseudo Jahn-Teller coupling occurs between the IE.' and the 3048 cm-l higher IAI' electronic states and has the effect of reducing the triplet-singlet excitation energy from 2613 cml to 275 cml in C 5 H6+. Thus, it is probable that vibrational-electronic interaction is an important factor in determining the relative stabilities of the singlet and the triplet states of these and related systems. Because coupling with the I A t' state is much stronger than interaction between the two degenerate lEI' components, the lowest singlet vibronic state of C6H6+ is totally symmetric, in contrast to the benzene anion. Comparison of the results for C6H6+, C6D6+' and C6Cl6+ shows that the extent of vibrational-electronic interaction and vibronic energy lowering are not very sensitive to moderate alterations in force constants and vibrational frequencies. The energy lowering in C 6 Cl 6 +, however, may be about 200 cml smaller than in C 5 H6+ if strong C-Cl, C-C vibration interactions are present. If the pentaphenyl derivative (Co6+) is treated by the point-mass approximation, the vibronic wavefunctions are expected to resemble closely those obtained for C.Ch+. The major factors determining the relative energies of the singlet and the triplet vibronic states in the C.X.+ cations are the IAI'_IE.' and the IE.'-3A.' electronic energy separations. While the latter is smaller in C.ci>.+ than in C5H6+, the two singlets are more widely spaced, so that a smaller vibronic energy lowering results. The energies of the IE.' and the IAI' vibronic states are obtained as a function of the IAI'_IE.' electronic separation.

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“…Theoretically, the electronic state of Bz dianion (Bz 2− ) has been studied by quantum chemical calculations. 2,3 It has been reported that the ground state is the triplet state, and the energy difference between the singlet state and triplet state is about 0.1 eV 2 or about 1 eV. 3 However, since the many body effects have not been fully treated and the energy difference is tiny, it has not yet been determined whether the ground state is the spin triplet state or the spin singlet state.…”

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confidence: 99%

Antiferromagnetic Exchange Interaction between Electrons on Degenerate LUMOs in Benzene Dianion
Matsuura
¹
,
Miyake
²
,
Fukuyama
³

2012
J. Phys. Soc. Jpn.
2
0
1
0
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Many aromatic hydrocarbons have doubly or multiply degenerate lowest unoccupied molecular orbitals (LU-MOs) consisting of 2pπ-orbitals. The exchange interaction between electrons on LUMOs in these dinegative ions tends to be considered as ferromagnetic (the spintriplet state) by the Hund's rule coupling. Indeed, the triplet ground state has been observed for the dinegative ions of triphenylbenzene, decacyclene, and so on. 1 Benzene (Bz) has doubly degenerate LUMOs. Theoretically, the electronic state of Bz dianion (Bz 2− ) has been studied by quantum chemical calculations. 2, 3 It has been reported that the ground state is the triplet state, and the energy difference between the singlet state and triplet state is about 0.1 eV 2 or about 1 eV. 3 However, since the many body effects have not been fully treated and the energy difference is tiny, it has not yet been determined whether the ground state is the spin triplet state or the spin singlet state. In addition, the ground state of Bz 2− has not been experimentally studied.In the present paper, we discuss the ground state of Bz 2− on the basis of the numerical diagonalization method of an effective model of π orbitals. Then, we estimate the amplitude of the exchange coupling between two electrons on LUMOs. As a result, we find that the ground state becomes the spin singlet state, and the exchange coupling between LUMOs can be antiferromagnetic.The model Hamiltonian for Bz 2− is given as follows:wherewhere χ's are atomic 2pπ orbitals of Bz; t π , U , U ′ , and J represent the transfer integral, the intra-and interorbital Coulomb interaction and the ferromagnetic exchange coupling, respectively. This effective model is an extended Hubbard model (t-U -V -J model). It is well known that the exchange coupling, J, plays a fundamental role in the property of the ground state. 4, 5The amplitude of U and t π have been estimated by the quantum chemical calculation: U ∼ 17 eV and t π ∼ 2.5eV. 6, 7 Thus, we choose U/t π = 7.0. The other parameters have also been estimated by the same quantum chemical calculations: U ′ ∼ 9 eV (U ′ /t π ∼ 3.6) and J ∼ 1 eV (J/t π ∼ 0.4). However, since we neglect many other interactions (for example, the second nearest Coulomb interactions), we regard U ′ and J as variable parameters.By diagonalizing the kinetic energy term H 0 , six molecular orbitals, φ 1 ∼ φ 6 , are given as follows: 7The eigen energy increases from φ 1 to φ 6 , while φ 2 (φ 4 ) and φ 3 (φ 5 ) are degenerate. We call φ 4 (φ 5 ) LUMO. In Fig. 1, we show the phase diagram for the ground state in the U ′ /t π -J/t π plane within manifolds of S = 2, S = 1, and S = 0. When J/t π is increased, the ground state changes from S = 1 to S = 0, and changes from S = 0 to S = 2. The S = 2 state is such that the spins of four holes become ferromagnetic by the ferromagnetic exchange coupling J. The characters of electronic states of the S = 1 state and S = 0 state are discussed later. Figure 2 shows the number of electrons in the molecular orbital φ i (eq.(4) ∼ eq.(9)) as a function of J/t...

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The ground state of the coronene dinegative ion

Cited by 7 publications

References 9 publications

Effect of Vibronic Interaction on the Singlet-Triplet Separation in Cyclopentadienyl Cations

Antiferromagnetic Exchange Interaction between Electrons on Degenerate LUMOs in Benzene Dianion

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The ground state of the coronene dinegative ion

Cited by 7 publications

References 9 publications

Synthesis and Characterization of Organolanthanidocene(III) (Ln = La, Ce, Pr, Nd) Complexes Containing the 1,4-Cyclohexa-2,5-dienyl Ligand (Benzene 1,4-Dianion): Structures of [K([18]-crown-6)][Ln{η5-C5H3(SiMe3)2-1,3}2(C6H6)] [Cp‘ ‘ = η5-C5H3(SiMe3)2-1,3; Ln = La, Ce, Nd]

Synthesis and Characterization of Organolanthanidocene(III) (Ln = La, Ce, Pr, Nd) Complexes Containing the 1,4-Cyclohexa-2,5-dienyl Ligand (Benzene 1,4-Dianion): Structures of [K([18]-crown-6)][Ln{η5-C5H3(SiMe3)2-1,3}2(C6H6)] [Cp‘ ‘ = η5-C5H3(SiMe3)2-1,3; Ln = La, Ce, Nd]

Effect of Vibronic Interaction on the Singlet-Triplet Separation in Cyclopentadienyl Cations

Antiferromagnetic Exchange Interaction between Electrons on Degenerate LUMOs in Benzene Dianion

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