[Cyanil]22− dimers possess long, two-electron ten-center (2e−/10c) multicenter bonding

García‐Yoldi, Íñigo; Miller, Joel S.; Novoa, Juan J.

doi:10.1039/b806900j

Cited by 37 publications

(41 citation statements)

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“…Theoretical studies indicated that all [TCNE] 2 2À dimers exhibit long, 2e À /4c (c = center) CÀC bonds, and are prototypes for long, multicenter C À C bonds between radical anions. More recently, long, multicenter C À C bonding has also been observed for [cyanil] 2 2À (2e À /10c (8C + 2O)), [11] [TTF] 2 2 + (TTF = tetrathiafulvalene) (2e À /10c (6C + 4S)), [13] di(2,5,8-tri-tert-butylphenalenyl) (2e À /14c (14C)), [14,15] [tetracyanopyrazine] 2 2À (2e À /8c (8C)), [16] [TCNQ] 2 2À (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, 2e…”

Section: + a C H T U N G T R E N N U N G [Tcne]mentioning

confidence: 91%

“…Additionally, dispersion also adds energetic stability to the [TCNE]C À ···A C H T U N G T R E N N U N G [TCNE]C À interaction. [10][11][12] The interaction between two [TCNE] ·À moieties is thus a long, multicenter C À C bond, because it differs from a conventional covalent bond in the genesis of the energetic stabilization, and longer equilibrium distances. Note that the [TCNE] 2 2À dimers present in [cation + ] 2 A C H T U N G T R E N N U N G [TCNE] 2 2À are diamagnetic, as they have a closed-shell singlet ground state, in good agreement with the experimental observations.…”

Section: + a C H T U N G T R E N N U N G [Tcne]mentioning

confidence: 99%

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Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Capdevila‐Cortada

Novoa

Bell

et al. 2011

Chemistry A European J

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The α, β, and δ polymorphs of [TTF][TCNE] (TTF=tetrathiafulvalene; TCNE=tetracyanoethylene) exhibit a new type of long, multicenter bonding between the [TTF](δ+) and [TCNE](δ-) moieties, demonstrating the existence of long, hetero-multicenter bonding with a cationic(δ+)···anionic(δ-) zwitterionic-like structure. These diamagnetic π-[TTF](δ+) [TCNE](δ-) heterodimers exhibit a transfer of about 0.5 e(-) from the TTF to the TCNE fragments, as observed from experimental studies, in accord with theoretical predictions, that is, [TTF(δ+)···TCNE(δ-)] (δ≅0.5). They have several interfragment distances <3.4 Å, and a computed interaction energy of -21.2 kcal mol(-1), which is typical of long, multicenter bonds. The lower stability of [TTF](δ+) [TCNE](δ-) with respect to typical ionic bonds is due, in part, to the partial electron transfer that reduces the electrostatic bonding component. This reduced electrostatic interaction, and the large interfragment dispersion stabilize the long, heterocationic/anionic multicenter interaction, which in [TTF(δ+)···TCNE(δ-)] always involves two electrons, but have ten, eight, and eight bond critical points (bcps) involving C-C, N-S, and sometimes C-S and C-N components for the α, β, and δ polymorphs, respectively. In contrast, γ-[TTF][TCNE] possesses [TTF](2)(2+) and [TCNE](2)(2-) dimers, each with long, homo-multicenter 2e(-)/12c (c=center, 2 C+4 S) [TTF](2)(2+) cationic(+)···cationic(+) bonds, as well as long, homo-multicenter 2e(-)/4c [TCNE](2)(2-) anionic(-)···anionic(-) bonding. The MO diagrams for the α, β, and δ polymorphs have all of the features found for conventional covalent C-C bonds, and for all of the previously studied multicenter long bonds, for example, π-[TTF](2)(2+) and π-[TCNE](2)(2-). The HOMOs for α-, β-, and δ-[TTF][TCNE] have 2c C-S and 3c C-C-C orbital-overlap contributions between the [TTF](δ+-) and [TCNE](δ-) moieties; these are the shortest intra [TTF···TCNE] separations. Thus, from an orbital-overlap perspective, the bonding has 2c and 3c components residing over one S and four C atoms.

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Section: + a C H T U N G T R E N N U N G [Tcne]mentioning

confidence: 91%

Section: + a C H T U N G T R E N N U N G [Tcne]mentioning

confidence: 99%

Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Capdevila‐Cortada

Novoa

Bell

et al. 2011

Chemistry A European J

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“…8 Other examples (Chart 2) include anionic species, e.g. 7,7,8,8-tetracyano-p-quinodimethanide ([TCNQ] •− ), 9−11 1,2,4,5-tetracyanobenzene ([TCNB] •− ), 12,13 1,2,4,5-tetracyanopyrazine ([TCNP] •− ); 14 cationic species, e.g., tetrathiafulvalenium ([TTF] + ); 15 and neutral radicals, e.g., substituted phenalenyl.…”

Section: Instructionmentioning

confidence: 97%

Large Nonlinear Optical Responses of Dimers Bearing a Donor and Acceptor: Long, Intradimer Multicenter Bonding

et al. 2014

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Unusual long, multicenter dimers bearing a large electron donor and acceptor have been the subject of great interest over the last decades due to their better conducting, superconducting, magnetic, or other physical properties. Twoelectron, multicenter bonding between two interplanar fragments has been recently recognized as a novel and important bonding interaction. Herein, the [TTF][TCNE], [TTF][TCNQ], [TTF][TCNP], and [TTF][TCNB] dimeric species have been studied by quantum mechanics methods with the view of assessing their interactions and first hyperpolarizabilities. It is found that the stabilities of the dimers primarily originate from the electrostatic bonding component. Although to a lesser extent, long, multicenter interactions due to the overlap of the molecular orbitals of the monomers are important also in the stability of these systems. Significantly, a severe hyperpolarizability decrease with changing the acceptor monomers of the dimeric species is qualitatively explained in terms of change in their charge transfer patterns. It indicates that the first hyperpolarizabilities of these dimers can be optimized by controlling their relative acceptor monomers. We believe that these results shall provide important information for further exploration of long, multicenter dimers with versatile and fascinating nonlinear optical properties.

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“…18 Computational studies have revealed the presence of such bond critical points in several dimers indicating a closed shell singlet ground state configuration. 14,[19][20][21] To the best of our knowledge, however, direct experimental evidence for such (3, −1) bond critical points from X-ray diffraction studies of radical dimers has not been reported.…”

Section: Electronic Structure and Bondingmentioning

confidence: 99%

Reversible Spin Pairing in Crystalline Organic Radicals

Rawson

Hayward

2013

Spin‐Crossover Materials

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The concept of high spin and low spin configurations in d-block complexes is taught in every undergraduate introduction to the coordination chemistry of the transition metals. In this situation the interplay between interelectron repulsion or 'pairing energy' (P E ) and crystal (ligand) field splitting ( ) determines the electronic structure and provides an elegant example of how chemical tuning and modification of the ligand donor set can manipulate electronic structure. When is of a similar magnitude to P E then there is a fine balance between crystal field stabilisation energy (an enthalpic term which favours the low spin configuration) and maximising the number of microstates (an entropic term which favours the high spin configuration). In these cases spin-transitions typically occur between a low temperature enthalpically stabilised low spin configuration and a high temperature entropically favoured high spin configuration. The ability to drive spin-transitions thermally, through light-irradiation or pressure-induced transitions are the focus of the rest of this book. In this chapter we consider organic 'spin-transition' materials whose electronic structures can be manipulated in a conceptually similar but substantially different chemical fashion, that is by examining the fine interplay between inter-electron repulsion (P E ) and promotion energy to a low-lying vacant orbital ( ) within the context of organic chemistry.In order to understand the behaviour of such systems we shall begin with a discussion (Section 8.2) of stable free-radicals and their tendency to associate to form dimers, focusing on computational and experimental studies of the electronic structures of these dimers in the gas phase and in solution. In Section 8.3 we extend these discussions to the solid state and investigate examples in which we observe (i) thermal population of electronic excited states leading to a gradual thermal evolution of paramagnetism upon warming and (ii) firstorder solid state phase transitions in which bond cleavage can lead to abrupt diamagnetic-paramagnetic phase Spin-Crossover Materials: Properties and Applications, First Edition. Edited by Malcolm A. Halcrow.

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[Cyanil]22− dimers possess long, two-electron ten-center (2e−/10c) multicenter bonding

Abstract: A long, two-electron ten-center (2e(-)/10c) [8 carbon plus 2 oxygen] bond in diamagnetic dimers of radical-anion tetracyano-1,4-benzoquinoneide (cyanil, [Q] (-)), [Q](2)(2-), is described by B3LYP and CASSCF(2,2)/MCQDPT calculations.

Cited by 37 publications

References 32 publications

Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Large Nonlinear Optical Responses of Dimers Bearing a Donor and Acceptor: Long, Intradimer Multicenter Bonding

Reversible Spin Pairing in Crystalline Organic Radicals

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[Cyanil]22− dimers possess long, two-electron ten-center (2e−/10c) multicenter bonding

Abstract: A long, two-electron ten-center (2e(-)/10c) [8 carbon plus 2 oxygen] bond in diamagnetic dimers of radical-anion tetracyano-1,4-benzoquinoneide (cyanil, [Q] (-)), [Q](2)(2-), is described by B3LYP and CASSCF(2,2)/MCQDPT calculations.

Cited by 37 publications

References 32 publications

Unusually Long, Multicenter, Cationδ+⋅⋅⋅Anionδ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Unusually Long, Multicenter, Cationδ+⋅⋅⋅Anionδ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Large Nonlinear Optical Responses of Dimers Bearing a Donor and Acceptor: Long, Intradimer Multicenter Bonding

Reversible Spin Pairing in Crystalline Organic Radicals

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Resources

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Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]

Unusually Long, Multicenter, Cation^δ+⋅⋅⋅Anion^δ−Bonding Observed for Several Polymorphs of [TTF][TCNE]