The Reversible Gel to Gel Transition of a Phosphonocarboxylate Functionalized Strandberg‐Type Polyoxometalate System

• Published in: ChemistrySelect (Weinheim) Vol. 9; no. 41
• Main Authors: Naulakha, Pragya, Kaushik, Priyanka, Raghavaiah, Pallepogu, Supriya, Sabbani
• Format: Journal Article
• Language: English
• Published: 04-11-2024
• Subjects: Covalent functionalization; Gel to gel transformation; Reversible sol‐gel; Stranberg polyoxometalate
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202302552

The Strandberg polyoxometalate (POM) metallogel Na4(H3O)2[(O2CC2H4PO3)2Mo5O15] (1) was synthesized in which the Strandberg cluster is functionalized by phosphonocarboxylate. The POM gel shows reversible sol to gel transition and gel to gel transition. The multiphase visual transitions between three states as a function of temperature and solvent are scarcely reported. The gel is characterized by temperature‐dependent and frequency‐dependent rheological studies and corresponding xerogels were characterized by FT‐IR, PXRD, FE‐SEM, EDX, TEM, and 31P NMR techniques. The stabilization of gel or obtaining single crystals from the same reaction mixture can be tuned by choice of counter cation. The single crystals of compound Cs14[(HO2CC2H4PO3)2Mo5O15]3·2Cl·10H2O (2) are obtained on addition of CsCl to compound 1 reaction mixture. Compound 2 is characterized by single crystal X‐ray diffraction. The compound 2 crystallizes in I2/a space group with unit cell parameters of a = 24.2415(16) Å, b = 10.4542(6) Å, c = 42.687(3) Å, α = 90°, β = 94.791°(3), and γ = 90°.
The reversible gel to gel transformation of phosphonocarboxylic acid functionalized Strandberg polyoxometalate system. The transparent gel is transformed into opaque gel on heating as well as treatment with ethanol. Opaque gel is transformed into the transparent gel on exposure to water vapor. The single crystals of phosphonocarboxylic acid functionalized Strandberg polyoxometalate are isolated with cesium as counter cation. The single crystal X‐ray diffraction structure shows extensive supramolecular interactions that can be correlated with soft interactions in the corresponding gel where the counter cation is sodium i. The electron microscopy of opaque gel is made up of extended network and transparent gel is made up of globular structures.