Naslov
Stacking of planar polyenic rings: from dispersion interactions to multicentric two-electron covalent bonding

Autori
Molčanov, Krešimir ; Kojić-Prodić, Biserka

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
The International Union of Crystallography (IUCr)'s Sagamore XIX - 2018 Conference on Quantum Crystallograpghy (QCr): Programme and Book of Abstracts / Matta, Cherif F. - Halifax : International Union of Crystallography, 2018, 98-98

ISBN
978-1-9993894-0-6

Skup
The International Union of Crystallography's Sagamore XIX - 2018 Conference on Quantum Crystallography

Mjesto i datum
Halifax, Kanada, 08.07.2018. - 13.07.2018

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
pi-stacking ; aromaticity ; quinones ; semiquinone radicals ; metal chelates

Sažetak
Stacking of aromatic rings is a well-known type of intermolecular interaction and has found its way into textbooks on supramolecular chemistry. It is usually considered as rather weak (typically <1 kcal mol-1) interaction, and that stacking is an exclusive property of aromatic rings ; the fact that other types of planar conjugated rings also stack is usually overlooked. Misconceptions about the very nature of stacking are also numerous, and are reflected in a variety of names used, which are often misleading: π∙∙∙π interaction, π-stacking, π-interaction, aromatic interaction, stacking interaction, etc. However, there is a growing amount of evidence that all rings stack, and that aromaticity is not a conditio sine qua non for formation of π-stacks. Stacking of planar organic radicals is known and has been used in design of organic semiconductors and magnetic materials. Our detailed studies have shown that interactions between quinoid rings and semiquinone radicals are by an order of a magnitude stronger than interactions between aromatic rings. As a result of numerous X-ray charge density studies on different types of stacked rings [5-7], we propose a generalised model of stacking, which accounts for both aromatic and non-aromatic rings. It is primarily based on our experimental X-ray charge density data of quinoid and semiquinoid rings and supported by quantum chemical computations. Our results show that: 1) non-aromatic planar polyenic rings can stack, 2) interactions are more pronounced between systems/rings with little or no π-electron delocalisation (e.g. quinones) than those involving delocalised systems (e.g. aromatics), 3) the main component of the interaction is electrostatic/multipolar between closed-shell rings, whereas 4) interactions between radicals involve a significant covalent contribution. Thus, stacking covers a wide range of interactions and energies ranging from weak dispersion to non-localised two-electron multicentric covalent bonding ('pancake bonding').

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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