Electrochemical molecular recognition of different charged and neutral guest species by redox-active receptive molecules is a fast-growing area of research in host-guest supramolecular chemistry. Ferrocene derivatives are popularly chosen for this purpose owing to their well-behaved electrochemical properties caused by the ferrocene moiety. The redox behavior of the ferrocene-based receptor molecules is sensitive to its interaction with the guest species lying in their proximity. Although various types of electrochemical sensors have been exploited in the construction of anion receptors, their synthetic pathways are complicated. To address the issues, we have synthesized simple bis(hydrazide) derivatives of ferrocene starting from 1,1’-ferrocene dicarboxylic acid and characterized the product spectroscopically as well as by single-crystal X-ray crystallography. We have chosen the hydrazide groups due to their ability to participate in hydrogen-bonding interactions with the guest anions, capable of forming H-bonds, keeping them in proximity of the iron center. We have explored the redox potential of 1,1’-bis(carbomethoxy)ferrocene, a precursor of bis(hydrazide), in the presence of monoanionic guests (HSO₄⁻, H₂PO₄⁻, CH₃COO⁻ and ClO₄⁻) and found that the potential of the Fe(II) center showed anodic shifts with all anions with the highest shift (70 mV) in the presence of HSO₄⁻. Since the dihydrazide receptor exhibited poor solubility in common organic solvents, we are currently working on replacing the hydrazide moiety with methylhydrazide with the aim that the methyl group makes the receptor more hydrophobic. Synthesis, characterization, and electrochemical behaviors of the receptor molecules and their interaction with the anionic guests will be presented.

Courteney Dufrene

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