Complexation of Imidazopyridine-Based Cations with a 24-Crown-8 Ether Host: [2]Pseudorotaxane and Partially Threaded Structures

Abstract

A new series of linear molecules derived from 1,2-bis(imidazopyridin-2-yl)ethane can fully or partially penetrate the cavity of the dibenzo-24-crown-8 macrocycle to produce a new family of host-guest complexes. Protonation or alkylation of the nitrogen atoms on the pyridine rings led to an increase in the guest total positive charge up to 4+ and simultaneously generated two new recognition sites (pyridinium motifs) that are in competition with the 1,2-bis(benzimidazole)ethane motif for the crown ether. The relative position of the pyridine ring and the chemical nature of the N-substituent determined the preferred motif and the host-guest complex geometry: (i) for linear guests with relatively bulky groups (i.e., a benzyl substituent), the 1,2-bis(benzimidazole)ethane motif is favored, leading to a fully threaded complex with a [2]pseudorotaxane geometry; (ii) for small substituents, such as -H and -CH3 groups, regardless of the guest shape, the pyridinium motifs are preferred, leading to external partially threaded complexes in a 2:1 host to guest stoichiometry.

Self-healing polymer materials constructed by macrocycle-based host–guest interactions

“…Crown ether has the longest history compared to other important macrocycles and was investigated for complexes with metal salts from the beginning. 39 Many organic salts, such as cationic imidazolium, 40 secondary ammonium 41 and pyridinium, 42 can form complexes with crown ethers. These self-assembled hostguest interactions respond to thermo-, pH-and ion-stimuli.…”

Monosulfonated dibenzo-24-crown-8 and its properties

“…Dibenzo-24-crown-8 ether (DB24C8) is one of the iconic macrocycles in supramolecular chemistry. Its use in the assembly of pseudorotaxanes [1][2][3][4][5][6][7][8][9][10][11][12][13] and mechanically interlocked molecules (MIMs) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] is widespread. The derivatives of DB24C8 play an equally important role; they are usually prepared by macrocyclization of the DB24C8 scaffold from appropriate pre-functionalized starting materials.…”

Hydrogen‐Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition

“…The N−H⋅⋅⋅N hydrogen bond formed between H‐bpy + cations affords a one‐dimensional (1D) polymer structure . Dibenzo‐24‐crown‐8 (DB‐24‐crown‐8), which can include whole heteroaromatic rings because of a larger ring size compared with 15‐crown‐4 and 18‐crown‐6, was selected as the “shuttle” part of the rotaxane. In addition to the large ring size, π–π interactions between the phenylene rings of DB‐24‐crown‐8 and the pyridyl rings of H‐bpy + should stabilize the pseudo‐polyrotaxane crystal.…”

“…The NÀH···N hydrogen bond formed between H-bpy + cations affords ao ne-dimensional (1D) polymer structure. [14] Dibenzo-24-crown-8 (DB-24-crown-8), which can include whole heteroaromatic rings because of al arger ring size compared with 15-crown-4 and 18-crown-6, [15][16][17][18] wass elected as the "shuttle" part of the rotaxane. In addition to the large ring size, p-p interactions betweent he phenylene rings of DB-24-crown-8 and the pyridyl rings of H-bpy + shouldstabilize the pseudo-polyrotaxanec rystal.C ompared with covalent bonds, hydrogen bonds have greater freedom in terms of bond lengtha nd angles, and the hydrogen bonds between Hbpy + lend flexibility to the crystal.…”