Substituted Azolium Disposition: Examining the Effects of Alkyl Placement on Thermal Properties

Abstract

We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for 1,3-dimethyl-4,5-bis(n-undecyl)imidazolium iodide (1-11), 1,3-dimethyl-4,5-bis(n-pentadecyl)- imidazolium iodide (1-15), and 1,2,3-trimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (2), which were found to adopt enantiotropic smectic A mesophases. Liquid-crystalline mesophases were not observed for 1,3-dimethyl-4,5-bis(n-heptyl)imidazolium iodide (1-7), 3-methyl-4,5-bis(n-penta-decyl)thiazolium iodide (3), and 2-amino-4,5-bis(n-pentadecyl)imidazolium chloride (4). Installing substituents in the 4- and 5-positions of the imidazolium salts appears to increase melting points while lowering clearing points when compared to data reported for 1,3-disubstituted analogues.

Understanding ionic mesophase stabilization by hydration: a solid-state NMR study

“…There has been a growing body of research aiming at the design of ILCs with an increasingly wider temperature range of the mesophase. 1,2,[6][7][8][9][10][11][12][13][14][15] The thermodynamic properties of ionic mesophases depending on composition have been thoroughly studied by systematic variation in the structure and properties of the constituting ions. For example, in heterocyclic imidazoliumbased ILCs, the trend of increasing mesophase temperature range in the anion order BF 4 o I o Br o Cl has been related to changes in charge delocalization properties and the hydrogen-bonding capabilities of the anions.…”

NMR Spectroscopic Studies of Cation Dynamics in Symmetrically-Substituted Imidazolium-Based Ionic Liquid Crystals

“…The imidazolium derivatives are the most popular cations for IL synthesis [ 9 ]. While the majority of studies have explored single-chain asymmetrically substituted imidazolium cores, there have been a number of recent reports on the investigation of imidazolium-based ILs with two symmetrically attached long alkyl chains [ 3 , 10 , 11 , 12 , 13 , 14 , 15 ]. Relocation of the polar and apolar domains provides a route to tune the physicochemical properties of ionic liquids while the enhanced rod-shape character of a symmetrically-substituted cation offers additional opportunities for self-assembly [ 13 , 16 ].…”

Anisotropic, Organic Ionic Plastic Crystal Mesophases from Persubstituted Imidazolium Pentacyanocyclopentadienide Salts

“…(50−54) We also reported 1,2,3-trimethyl-4,5-bis(n-pentadecyl)imidazolium iodide to be the first example of a LC pentasubstituted imidazolium salt. (55) We describe here how the previously reported synthetic methodology may be extended to obtain [(Cn)5im][X] salts that feature alkyl substituents larger than a methyl group (i.e., n-C7H15, n-C11H23 or n-C15H31). Derivatives with planar nitrate ([NO3] − ) or "π-electronic" pentacyanocyclopentadienide ([Cp(CN)5] − ) anions (Scheme 1) were subsequently prepared from the halide salts by anion metathesis.…”

“…Recently, some of us prepared 4,5-dialkylsubstituted imidazoles with relatively long alkyl substituents by utilizing Radziszewski-type chemistry as a key step. The corresponding 1,3-dimethylimidazolium salts were obtained upon methylation and applied as lipid analogues in model cell systems or used as precursors for N -heterocyclic carbenes for the stabilization of nanoparticles. − We also reported 1,2,3-trimethyl-4,5-bis­( n -pentadecyl)­imidazolium iodide to be the first example of a LC pentasubstituted imidazolium salt …”