Mössbauer effect and electron paramagnetic resonance investigation of some complexes of iron with ‘persulphide’ ligands

Abstract

⁵⁷ Fe Mössbauer effect and e.p.r. spectra have been measured for the low-spin iron(III) complexes Fe(ttd)₂(dtt), Fe(ttd)(dtt)₂, and Fe(dtt)₃, CHCl₃(ttd = trithioperoxy-p-toluate, dtt = dithio-p-toluate). Similar Mössbauer spectra were observed for all three complexes with values of isomer shift and quadrupole splitting characteristic of low-spin iron(III) complexes. The isomer shift of Fe(dtt)₃, CHCl₃ was significantly higher than that of the other complexes, a consequence of the greater ability of the dtt ligand than ttd to accept electrons from the metal by backdonation. The quadrupole splittings for all complexes were similar in magnitude but the sign of the principal component of the electric field gradient tensor was found to be negative for Fe(ttd)₂(dtt) and Fe(ttd)(dtt)₂ but positive for Fe(dtt)₃, CHCl₃. E.p.r. spectra of frozen chloroform solutions of Fe(ttd)₂(dtt) and Fe(ttd)(dtt)₂ were observed at 100 K. The experimental data suggest that the ground state of these two complexes is a d_xy hole, whereas for the compound Fe(dtt)₃, CHCl₃, for which no e.p.r. spectrum was detectable, the ground state is probably an equal mixture of d_xz and d_yz holes.