Evidence for Multicenter Bonding in Dianionic Tetracyanoethylene Dimers by Raman Spectroscopy

Casado, Juan; Burrezo, Paula Mayorga; Ramı́rez, Francisco J.; Navarrete, Juan T. López; Lapidus, Saul H.; Stephens, Peter W.; Vo, Hoa Lan; Miller, Joel S.; Mota, Fernando; Novoa, Juan J.

doi:10.1002/anie.201207813

Cited by 35 publications

(19 citation statements)

References 23 publications

(21 reference statements)

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“…These strong interactions are probably of the same nature as those in dimers of tetracyanoethylene radical anions (TCNE, Fig. 6) (Novoa & Miller, 2007;Tian & Kertesz, 2011;Casado et al, 2013;Cui et al, 2014a), which have been interpreted as multicentric covalent bonding. The term 'pancake bonding' (Preuss, 2014;Kertesz, 2018) has recently been introduced to describe interactions in close dimers of radicals.…”

Section: Stacked Radicals Involve Unlocalized Covalent Interactionsmentioning

confidence: 93%

Towards understanding π-stacking interactions between non-aromatic rings

Molčanov

Kojić‐Prodić

2019

IUCrJ

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The first systematic study of π interactions between non-aromatic rings, based on the authors' own results from an experimental X-ray charge-density analysis assisted by quantum chemical calculations, is presented. The landmark (non-aromatic) examples include quinoid rings, planar radicals and metal-chelate rings. The results can be summarized as: (i) non-aromatic planar polyenic rings can be stacked, (ii) interactions are more pronounced between systems or rings with little or no π-electron delocalization (e.g. quinones) than those involving delocalized systems (e.g. aromatics), and (iii) the main component of the interaction is electrostatic/multipolar between closed-shell rings, whereas (iv) interactions between radicals involve a significant covalent contribution (multicentric bonding). Thus, stacking covers a wide range of interactions and energies, ranging from weak dispersion to unlocalized two-electron multicentric covalent bonding (`pancake bonding'), allowing a face-to-face stacking arrangement in some chemical species (quinone anions). The predominant interaction in a particular stacked system modulates the physical properties and defines a strategy for crystal engineering of functional materials.

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Section: Stacked Radicals Involve Unlocalized Covalent Interactionsmentioning

confidence: 93%

Towards understanding π-stacking interactions between non-aromatic rings

Molčanov

Kojić‐Prodić

2019

IUCrJ

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“…Characteristic interlayer vibrational modes are present. [29] The systemsd iscussed in this review consist of p-conjugated molecules with p-electrons on frameworks built from C, N, B, O, S, (and occasionally Se) [30] atoms supplemented by typical organic groups and halogens. Additional elements may occur in doping and will be briefly mentionedf or layered 2D systems with extended pancake bonding.…”

Section: Introductionmentioning

confidence: 99%

Pancake Bonding: An Unusual Pi‐Stacking Interaction

Kertész

2018

Chemistry A European J

196

227

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A category of parallel π-stacking interaction, termed pancake bonding, is surveyed. The main characteristics are: the interaction occurs among radicals with highly delocalized π-electrons in their singly occupied molecular orbitals (SOMOs), the contact distances in the π-stacking direction are shorter than the typical van der Waals distances, and the stabilization obtained by the bonding combination of the SOMO orbitals leads to direct atom-to-atom overlap with strong orientational preferences. These atypical intermolecular interactions contain a component of electron sharing between the radicals that can be viewed as covalent-like. Pancake bonded dimers characteristically have low-lying singlet and triplet states and show characteristic interlayer vibrational modes. Pancake bonded aggregates serve as molecular components in many conducting and other functional organic materials. The role of van der Waals (vdW) interactions in pancake bonded dimers, chains, and other aggregates is different from closed shell vdW aggregates: here the Pauli repulsions reduce the attractive dispersion interaction significantly. Fluxionality between π- and σ-bonded aggregates often occur in the context of pancake bonding. Both experimental and computational aspects are reviewed.

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“…Forfurther investigation of the bonding structure of 1,we measured the Raman spectra of the powder samples of 1 and 2 ( Figure 5). [12] Forboth 1 and 2,the strongest peaks were the C = Cstretching modes of the phenyl rings around 1600 cm À1 , and their frequencies were almost same (for 1;1601 cm À1 ,for 2;1595 cm À1 )i ns pite of the apparent quinoidal deformation of 1.T he most remarkable difference was found in the peaks around 1300 cm À1 region, which could be assigned to the CÀN stretching and the aromatic C À Hbending modes. [13] For 2,the peak was assigned to the peak at 1321 cm À1 .Incontrast, for 1, this peak was split into two peaks (1256 and 1294 cm À1 ).…”

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confidence: 89%

A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed‐Shell Electronic State

et al. 2015

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Reported herein is the structure and the electronic properties of a novel triphenylamine derivative having two phenoxy radicals appended to the amino nitrogen atom. X-ray single crystal analysis and the magnetic resonance measurements demonstrates the unexpected closed-shell electronic structure, even at room temperature, of the molecule and two unusual C-N bonds with multiple-bond character. The theoretical calculations support the experimentally determined molecular geometry with the closed-shell electronic structure, and predicted a small HOMO-LUMO gap originating from the nonbonding character of the HOMO. The optical and electrochemical measurements show that the molecule has a remarkably small HOMO-LUMO gap compared with its triphenylamine precursor.

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Evidence for Multicenter Bonding in Dianionic Tetracyanoethylene Dimers by Raman Spectroscopy

Cited by 35 publications

References 23 publications

Towards understanding π-stacking interactions between non-aromatic rings

Towards understanding π-stacking interactions between non-aromatic rings

Pancake Bonding: An Unusual Pi‐Stacking Interaction

A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed‐Shell Electronic State

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