Electrochemistry and Stability of 1,1'-Ferrocene-Bisphosphonates

Melissa Egger; Ingo Koehne; Dominik Wickenhauser; Werner Schlemmer; Stefan Spirk; Rudolf Pietschnig

doi:10.1021/acsomega.2c07234

Electrochemistry and Stability of 1,1'-Ferrocene-Bisphosphonates

ACS Omega. 2023 Mar 9;8(12):10899-10905. doi: 10.1021/acsomega.2c07234. eCollection 2023 Mar 28.

Authors

Melissa Egger¹, Ingo Koehne², Dominik Wickenhauser¹, Werner Schlemmer¹, Stefan Spirk¹, Rudolf Pietschnig²

Affiliations

¹ Institute of Bioproducts and Paper Technology, Graz University of Technology, Inffeldgasse 23, 8010 Graz, Austria.
² Institute of Chemistry and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.

Abstract

Here, we investigate the electrochemical properties and stability of 1,1'-ferrocene-bisphosphonates in aqueous solutions. ³¹P NMR spectroscopy enables to track decomposition at extreme pH conditions revealing partial disintegration of the ferrocene core in air and under an argon atmosphere. ESI-MS indicates the decomposition pathways to be different in aqueous H₃PO₄, phosphate buffer, or NaOH solutions. Cyclovoltammetry exhibits completely reversible redox chemistry of the evaluated bisphosphonates, sodium 1,1'-ferrocene-bis(phosphonate) (3) and sodium 1,1'-ferrocene-bis(methylphosphonate) (8), from pH 1.2 to pH 13. Both the compounds feature freely diffusing species as determined using the Randles-Sevcik analysis. The activation barriers determined by rotating disk electrode measurements revealed asymmetry for oxidation and reduction. The compounds are tested in a hybrid flow battery using anthraquinone-2-sulfonate as the counterside, yielding only moderate performance.