High-frequency EPR study of the high-spin FeII complex Fe[(SPPh2)2N]2

We report continuous-wave electron-paramagnetic-resonance (EPR) spectra of the high-spin FeII complex Fe[(SPPh2)2N]2 at 275.7 GHz, 94.1 GHz and 9.5 GHz. Combined analysis of these EPR spectra shows that the complex occurs in multiple conformations. For two main conformations the spin-Hamiltonian parameters, which reflect the electronic structure of the complex, are accurately determined: (1) D=9.17cm-1 (275 GHz), E/D=0.021 and (2) D=8.87cm-1 (266 GHz), E/D=0.052. The EPR spectra obtained at 275.7 GHz on single crystals of the complex are essential for the analysis and in addition they reveal that the two main conformations occur at two magnetically distinguishable sites.

63Highlights► Multi-frequency EPR has allowed the study of a high-spin Fe(II) complex. ► Analysis of powder EPR spectra at 9, 95 and 275 GHz. ► Analysis of crystal EPR spectra at 275 GHz. ► Conformational flexibility of iron-sulfur coordination observed. ► Each unit cell contains the complex in two conformations.