High-pressure EPR spectroscopy: paramagnetic exchange of organic radicals with iron (III) acetylacetonate

Abstract

In this work the spin exchange between organic radicals and a paramagnetic transition metal complex is studied as a function of pressure. Spin exchange rate constants of the tetracyanoethene radical anion (TCNE^•−) and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) with iron (III) acetylacetonate (Fe(acac)₃) were measured at elevated pressures with the help of electron paramagnetic resonance (EPR) spectroscopy. As the reactions are diffusion controlled, the effect of pressure on the paramagnetic exchange is examined by comparison of experimental rate constants, determined from line-broadening experiments, with the corresponding theoretical ones. The activation volumes of the reactions were between 4 and 8 mol⁻¹ cm³, consistent with results reported in literature.

Keywords:

• electron paramagnetic resonance
• paramagnetic exchange
• diffusion
• high-pressure chemistry

Acknowledgements

Tajamal Hussain thanks the Higher Education Commission (HEC), Pakistan, for a PhD scholarship. Gunter Grampp gratefully acknowledges the financial support of the Austrian Exchange Service (OeAD). This work was supported by an Austrian Science Foundation grant (FWF-Project No. P22677).