When a single hole aligns several spins: Double exchange in organic systems

Trinquier, Georges; Chilkuri, Vijay Gopal; Malrieu, Jean‐Paul

doi:10.1063/1.4878498

Cited by 4 publications

(1 citation statement)

References 52 publications

(35 reference statements)

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“…To end this study, we wish to address the somewhat more intricate cases in which Lewis full conjugation of all double bonds can only reduce the total spin, without completely killing it, a situation met incidentally in other circumstances. [25,42] This situation will be illustrated on derivatives of 3 and 3' spiked with lateral methylene groups. In 3 c, two meta-trimethylene-benzene groups are coupled antiferromagnetically through a para-benzene (Scheme 8).…”

Section: Lowering the Total Spin Without Quenching It Entirelymentioning

confidence: 99%

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

Trinquier

Malrieu

2014

Chemistry A European J

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Some conjugated alternant hydrocarbons, of singlet ground state according to Ovchinnikov's rule, may exhibit strong polyradical character, despite admitting complete pairing of electrons in bond orbitals between adjacent atoms. Typical organizations of this kind are encountered in polycyclic frames supporting two or more extracyclic methylene groups. Lewis bond pairing would require quinonization of six-membered rings, whereas safeguarding aromaticity proves sufficient to impose ground-state open-shell character, that is, the existence of unpaired electrons, providing the number of benzene rings to be quinonized is larger than two. Several examples built as variations around para-polyphenylene frames are examined through unrestricted DFT (UDFT) calculations, using various methods for spin decontamination of wavefunctions, geometries, and singlet-triplet energy gaps. They all illustrate how it is possible to conceive architectures that can be written with a closed-shell bond pairing, although they exhibit a large number of unpaired electrons. The same analyses also apply to systems in which quinonization would not kill but only reduce the number of unpaired electrons.

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Section: Lowering the Total Spin Without Quenching It Entirelymentioning

confidence: 99%

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

Trinquier

Malrieu

2014

Chemistry A European J

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Sigma‐ versus Pi‐Dimerization Modes of Triangulene

Mou

Kertész

2018

Chemistry A European J

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We show that the diradicaloid triangulene, a graphene nano-flake molecule, can aggregate in a variety of dimerization modes. We found by density functional theory modeling a number of triangulene dimers including six doubly bonded σ-dimers in addition to the previously reported six pancake bonded π-dimer isomers. The σ-dimers display a wide range of stabilities: the interaction energy of the most stable σ-dimer is -25.17 kcal mol . Besides the doubly bonded σ-dimers with closed shell ground states, we also found an open-shell singly σ-bonded diradicaloid dimer. We found an interesting isomerization route between a doubly bonded σ-dimer, a singly bonded σ-dimer with a low-lying triplet state and two π-bonded dimers with low-lying quintet states. Derivatives of triangulene, trioxo-triangulenes (TOTs) have been previously characterized experimentally. Here, we show the reasons why so far only the π-dimer but not the σ-dimer was experimentally observed for all TOTs.

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Spin polarization effects in trigonal mixed-valence complexes exhibiting double exchange supported by external spin-cores

Palii,

Korchagin,

Kondrina

et al. 2023

The Journal of Chemical Physics

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The theory of the magnetic coupling between the localized spins, mediated by the mobile excess electron, is generalized to the case of a trigonal, six-center, four-electron molecule with partial valence delocalization. The combination of the electron transfer occurring within the valence-delocalized subsystem and the interatomic exchange producing coupling of the spin of the mobile electron of valence-delocalized fragment with the three localized spins forming the valence-localized subsystem leads to the appearance of a special kind of double exchange (DE), termed the “external core double exchange” (ECDE), in order to distinguish such DE from the conventional “internal core double exchange” for which the mobile electron is coupled with the spin-cores on the same center via the intra-atomic exchange. The effect of the ECDE on the ground spin state of the considered trigonal molecule is compared with earlier reported effect produced by DE in the four-electron, mixed-valence (MV) trimer. A high diversity of the ground spin states is revealed, depending on the relative magnitudes and signs of the electron transfer and interatomic exchange parameters, with part of these states not appearing to be the ground states in a trigonal trimer exhibiting DE. We briefly discuss some examples of trigonal MV systems from the point of view of the possibility to have different combinations of signs of the transfer and exchange parameters and, accordingly, different ground spin states. The tentative role of the considered systems in molecular electronics and spintronics is also noticed.

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When a single hole aligns several spins: Double exchange in organic systems

Cited by 4 publications

References 52 publications

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

Sigma‐ versus Pi‐Dimerization Modes of Triangulene

Spin polarization effects in trigonal mixed-valence complexes exhibiting double exchange supported by external spin-cores

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