Herring‐bone π–π interactions in trans‐2,6‐diphenyl‐2,3,5,6‐tetrahydrothiapyran‐4‐one

The structure of the title compound, C₁₇H₁₆OS, is primarily stabilized by T‐shaped and parallel‐displaced aromatic clusters. The distances between the centroids of the aromatic pairs are in the range 4.34–5.30 Å. In the crystal packing, the mol­ecules dimerize by means of π–π interactions of both face‐to‐face and edge‐to‐face types, and the aromatic rings associate in a cyclic edge‐to‐face tetrameric arrangement of the herring‐bone type. These herring‐bone interactions appear to insulate hydrogen‐bond interactions in the crystal structure.     

Substituted 4‐alkoxy‐7‐Cl‐quinolines exhibiting π–π stacking

The molecules of 4‐allyloxy‐7‐chloroquinoline, C₁₂H₁₀ClNO, (I), 7‐chloro‐4‐methoxyquinoline, C₁₀H₈ClNO, (II), and 7‐chloro‐4‐ethoxyquinoline, C₁₁H₁₀ClNO, (III), are all planar. In all three structures, π–π interactions between the quinoline ring systems are generated by unit‐cell translations along the a axes, irrespective of space group. These structures are the first reported for 4‐alkoxyquinolines.     

Noncovalent Lone Pair⋅⋅⋅(No‐π!)‐Heteroarene Interactions: The Janus‐Faced Hydroxy Group

A comparative study using NMR spectroscopy and designed top‐pan molecular balances demonstrates that the noncovalent interaction of a hydroxy group with π‐deficient pyrazine and quinoxaline units involves a lone pair–heteroarene interaction which is much stronger and solvent independent when measured relative to the classical π‐facial hydrogen bond to a benzene ring. Alkyl fluorides also prefer the heteroarene rings over the benzene ring. The attractive interaction between a quinoxaline and a terminal alkyne is also stronger than the intramolecular hydrogen bond to an arene.     

The peptide NCbz‐Val‐Tyr‐OMe and aromatic π–π interactions

The peptide N‐benzyloxycarbonyl‐L‐valyl‐L‐tyrosine methyl ester or NCbz‐Val‐Tyr‐OMe (where NCbz is N‐benzyloxycarbonyl and OMe indicates the methyl ester), C₂₃H₂₈N₂O₆, has an extended backbone conformation. The aromatic rings of the Tyr residue and the NCbz group are involved in various attractive intra‐ and intermolecular aromatic π–π interactions which stabilize the conformation and packing in the crystal structure, in addition to N—H...O and O—H...O hydrogen bonds. The aromatic π–π interactions include parallel‐displaced, perpendicular T‐shaped, perpendicular L‐shaped and inclined orientations.     

Redox‐Switchable 20π‐, 19π‐, and 18π‐Electron 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrinoid Nickel(II) Complexes

The first examples of air‐stable 20π‐electron 5,10,15,20‐tetraaryl‐5,15‐diaza‐5,15‐dihydroporphyrins, their 18π‐electron dications, and the 19π‐electron radical cation were prepared through metal‐templated annulation of nickel(II) bis(5‐arylamino‐3‐chloro‐8‐mesityldipyrrin) complexes followed by oxidation. The neutral 20π‐electron derivatives are antiaromatic and the cationic 18π‐electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso N atoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20‐tetraarylporphyrins.     

Construction of Hetero‐Four‐Layered Tripalladium(II) Cyclophanes by Transannular π⋅⋅⋅π Interactions

A synthetic strategy for the generation of new molecular species utilizing a provision of nature is presented. Nano‐dimensional (23(2)×21(1)×16(1) ų) hetero‐four‐layered trimetallacyclophanes were constructed by proof‐of‐concept experiments that utilize a suitable combination of π???π interactions between the central aromatic rings, tailor‐made short/long spacer tridentate donors, and the combined helicity. The behavior of the unprecedented four‐layered metallacyclophane system offers a landmark in the development of new molecular systems.     

Hetero‐π‐Dimers of Phenalenyls

Homogeneous π‐stacking dimers of phenalenyl and its derivatives have gained tremendous interest as components of conducting organic materials. For the first time, we investigate theoretically heterogeneous phenalenyl π‐dimers. Key parameters, including charge transfer, interaction energy, singly occupied molecular orbital (SOMO) energy, and spin density, are studied with the help of density functional theory. We find that the amount of charge transfer between the two monomers in phenalenyl π‐dimers correlates with the difference in the SOMO energies of the constituent monomers, where the SOMO energy plays the role of a monomer (group) electronegativity index. Charge transfer plays an important role in stabilizing the heterodimers while maintaining a significant diradicaloid character. For five heterodimers the interaction energy is found to be as large as ?30 to ?50 kcal mol^?1. The presented correlation between the monomer SOMO energy levels and their stability can provide a simple predictive tool to design new highly stable π‐stacking heterodimers.     

“Dumbbell”‐ and “Clackers”‐Shaped Dimeric Derivatives of Monocarba‐closo‐dodecaborate

We designed, synthesized, and characterized two types of dimeric forms of monocarba‐closo‐dodecaborate, namely, a “dumbbell”‐shaped dianion having a C?C bond and a “clackers”‐shaped monoanion having an iodonium linker. The unique architectures of these anionic molecules were established by X‐ray analysis. Spectroscopic analysis, DFT calculations, and reactivity experiments revealed high anionic and chemical stability of both anions, which are crucial properties for weakly coordinating anions.