Facile crystallization of 2-phenyl benzimidazole-5-sulfonic acid: Characterization of lattice water dependent zwitterionic supramolecular forms, with modulation in proton conductivities

Abstract

A facile aqueous medium crystallization strategy has been found for this water insoluble title compound. Two crystalline forms, differing in the number of lattice water molecules (mono hydrated; form I & di-hydrated; form II), have been obtained, depending on the duration of crystallization. X-ray structural studies reveal that the compound crystallizes in the zwitterionic state in both the forms, due to the protonation of one imidazole nitrogen by-SO 3 H group, are engaged in hydrogen bonded interactions, involving lattice water molecule(s), and thus the supramolecular arrangements of the forms are influenced by lattice waters. Additional water molecules in the form II make it more hydrophilic, as confirmed using contact angle measurements. Procedures were optimized for better crystalline yields, and the bulk purity were ascertained by TGA, elemental and PXRD analysis. AC impedance measurements prove that both the crystalline forms are indeed proton conducting electrolytes, with magnitudes of 1 × 10 −5 S cm −1 and 5 × 10 −5 S cm −1 for form I & II, respectively under humidified conditions at 25 • C. Proton conducting performance of II has been found to be greater than I and could be correlated with its higher hydrophilicity and enriched hydrogen bonds for Grotthuss mechanism.

Multifunctional Viologen-Derived Supramolecular Network with Photo/Vapochromic and Proton Conduction Properties

“…The proton conductivity of 1 is not comparable to the ultrahigh proton conductivity of hydrogen-based organic framework (HOF) materials HOF-GS-10 (0.75 × 10 −2 S cm −1 ) and HOF-GS-11 (1.8 × 10 −2 S cm −1 ) at 30 °C and 95% relative humidity (RH), respectively [ 31 ]. However, it is several orders of magnitude higher than other reported HOFs, such as HOF-H 3 L (6.91 × 10 −5 S cm −1 ) at 100 °C and 98% RH [ 32 ], hydrated HOF-6a (3.4 × 10 −6 S cm −1 at 300 K and ∼97 % RH) [ 21 ] and the pair of zwitterionic supramolecular structures of 2-phenylbenzimidazole-5-sulfonicacid, with magnitudes of 1 × 10 −5 S cm −1 for the mono-hydrated form and 5 × 10 −5 S cm −1 for the di-hydrated form [ 33 ]. The decent proton conductivity of compound 1 may be explained by the continuous hydrogen bond pathway established by the ligands, guest water molecules and nitrate ions, as discussed in the structural section ( Figure 1 b) [ 34 ].…”

Improvement of Age-Resistance of LDPE-Based Nanocomposite Films by Addition of a Modified Layered Double Hydroxide with an Anionic UV Screener

“…Figure 1 shows the normalized intensity of the FT-IR spectra of PBS, chloride-LDH, and PBS-LDH. Neat PBS presents a peak at 1190 cm −1 , ascribed to the asymmetric stretches of the sulfonate group [26]. The symmetric stretching vibrations of the group correspond to the wavenumbers from 1030 cm −1 to 1090 cm −1 .…”