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

  • D SaravanabharathiEmail author
  • M Obulichetty
  • M Kumaravel
Regular Article


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 –\(\hbox {SO}_{3}\hbox {H}\) 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 \(1 \times 10^{-5}\,\hbox {S cm}^{-1}\) and \(5 \times 10^{-5}\,\hbox {S cm}^{-1}\) for form I & II, respectively under humidified conditions at \(25\,^{\circ }\hbox {C}\). 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.

Graphic Abstract

Two lattice water dependent supramolecular forms and their influence in the spectroscopic and proton conductivity results of the materials are discussed. SYNOPSIS Simple crystallization strategies for this water-insoluble title compound were identified. X-ray studies show occurrences of two lattice water dependent forms. Crystalline forms are distinguishable using spectroscopic techniques. Form II has been shown to be a better humidity based proton electrolyte than I.


2-Phenyl benzimidazole-5-sulfonic acid aqueous crystallization lattice water dependent supramolecular structures proton conduction 



This work was initially supported by the Start up Research Grant of the Science and Engineering Research Board (SERB), New Delhi that ended on 13.08.2016. Corresponding author gratefully acknowledge the SERB for providing the financial assistance (SB/FT/CS-184/2011dated 10.07.2013). Authors wish to thank the Principal and Management of the PSG College of Technology for the facilities. Authors wish to thank Mr. S. S. Subramanian, Asst. Prof. Department of Applied Science, PSGCT, for the contact angle measurements. Authors sincerely thank the SAIF - IIT Madras for single crystal data collection, solving and refining of the structures. Authors further wish to thank the STIC-Cochin for the elemental and the TGA analyses, and the Karunya University, Coimbatore for PXRD measurements.

Supplementary material

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Copyright information

© Indian Academy of Sciences 2019

Authors and Affiliations

  • D Saravanabharathi
    • 1
    Email author
  • M Obulichetty
    • 2
  • M Kumaravel
    • 1
  1. 1.Department of ChemistryPSG College of TechnologyCoimbatoreIndia
  2. 2.Department of Applied SciencePSG College of TechnologyCoimbatoreIndia

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