Hydrogen-bridged chelate ring-assisted π-stacking interactions

Abstract

A salicylideneaniline (SA) derivative, (6Z)-6-({[2-(hydroxymethyl)phenyl]amino}methylidene)-3,5-dimethoxycyclohexa-2,4-dien-1-one monohydrate, has an increased aromaticity within its hydrogen-bridged chelate ring owing to its NH character. In the reported crystal structure, nonconventional π-stacking interactions, which are referred to as hybrid π-stacking interactions, are observed between a quasiaromatic chelate ring, formed as a result of the resonance-assisted intramolecular hydrogen bond and ordinary aromatic rings. Besides, π-stacking interactions are also seen between two hydrogen-bridged quasiaromatic chelate rings, which are referred to as pure π-stacking interactions. A CSD search has revealed that both kinds of interactions are frequently observed in molecular crystals of SA derivatives in fully or partially NH tautomeric form, and aromaticity levels of certain fragments of SA derivatives have dramatic effects on their stacking arrangements. These interactions are distinguished from the usual π···π interactions by their formation character, i.e. both σ- and π-deficient and σ-deficient character of pure interactions is more pronounced than that of the hybrid ones.

Very Strong Parallel Interactions Between Two Saturated Acyclic Groups Closed with Intramolecular Hydrogen Bonds Forming Hydrogen-Bridged Rings

“…The data in Figure 3 show that most of the parallel contacts have the normal distances between 3.0 and 3.5 Å. These are distances typical for stacking of organic aromatic rings (3-4 Å) [17][18][19][20][21][22] and other planar rings that form stacking interactions [24][25][26][27][43][44][45][46]. The data in Figure 3 show that most of the parallel contacts have the normal distances between 3.0 and 3.5 Å.…”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…[7,36,40,55,92,264,[357][358][359] RAHB rings are capable of forming analogous p···p or p···HÀCi nteractions, reflectingt heir aromatic or metalloaromatic nature. [7,36,40,55,92,264,[357][358][359] RAHB rings are capable of forming analogous p···p or p···HÀCi nteractions, reflectingt heir aromatic or metalloaromatic nature.…”

“…[7,36,40,55,92,264,[357][358][359] RAHB rings are capable of forming analogous p···p or p···HÀCi nteractions, reflectingt heir aromatic or metalloaromatic nature. [357] Moreover, p-stacking interactions are also found between two RAHB rings in this structure. [357] Moreover, p-stacking interactions are also found between two RAHB rings in this structure.…”

“…The relevant centroids of the hybrid p···p stacking interactions are denoted as Ch1 for the RAHB chelate, Ch2 for the substituted salicylidene (aromatic), and Ch3 for the phenylmethanol ring (aromatic). [357] Scheme89. Cholesterol-modified RAHB-containing hydrazone switch.…”

“…Cholesterol-modified RAHB-containing hydrazone switch. [357] Both types of RAHB interactions are of great importance in crystal engineering, given that changes in molecular geometries of these types of compounds are accompanied by noncovalent interactions in their molecular crystals and vice versa, and this can be au seful tool in the manipulation of molecular buildingb locks in crystals. (6Z)-6-({[2-(hydroxymethyl)phenyl] amino}-methylidene)-3,5-dimethoxycyclohexa-2,4-dien-1-one (a) and RAHB-assisted p-stacking interactions therein (b).…”