Analysis of Electron Paramagnetic Resonance Spectra with Very Large Quadrupole Couplings

Abstract

Frozen solution electron paramagnetic resonance (EPR) spectra are reported for [(η 4 -cod)Rh(µ-RNNNR) 2 -Ir(CO) 2 ] + (cod ) 1,5-cyclooctadiene), [(PPh 3 )(CO)Rh(µ-RNNNR) 2 Ir(CO)(PPh 3 )] + (R ) p-tolyl) and [Tp′Ir-(CO)(PPh 3 ] + (Tp′ ) hydrotris(3,5-dimethylpyrazolyl)borate). In the first spectrum, the Rh hyperfine coupling dominates and there are no significant quadrupolar effects. In the second spectrum, the low-field (g x and g y ) features are 1:2:1 triplets rather than 1:1:1:1 quartets (I ) 3 / 2 for 191 Ir and 193 Ir), and in the third, the x and y features appear to be doublets. These anomalies result from the very large quadrupole moment for the iridium isotopes. This can be partially understood from a perturbation theory treatment, but quantitative simulations require direct matrix diagonalization and careful treatment of the problem, with respect to the orientation of the electron spin and nuclear spin quantization axes. The theoretical aspects of the calculations are presented, together with an interpretation of the results in terms of the electronic structures of the complexes.

Redox Non-innocence of Thioether Macrocycles: Elucidation of the Electronic Structures of Mononuclear Complexes of Gold(II) and Silver(II)

“…It is this latter effect that we observe in [Au([9]aneS 3 ) 2 ] 2+ . A thorough investigation of these effects on powder EPR spectra has been reported for a range of Ir(II) complexes ,,7b,7c, Through simulation of the EPR spectra of [Au([9]aneS 3 ) 2 ] 2+ , we find that the “two-plus-two” distortions of the g zz and g yy hyperfine quartets can only be reproduced by introduction of both a non-zero rhombic quadrupole parameter η and a non-zero angle of twist ρ of the P tensor with respect to the g and A matrices about the x axis.…”

MoV Electron Paramagnetic Resonance of Sulfite Oxidase Revisited: The Low-pH Chloride Signal

“…Unless the quadrupole coupling is very large, 29 quadrupole effects are usually manifested as additional transitions approximately within the envelope of the hyperfine splitting. 30,31 Furthermore, no obvious quadrupole effects are observed in the EPR spectra of other transition metal ions exhibiting chlorine hyperfine coupling. 32,33 As we observe only a broadening, our estimates of hyperfine couplings will necessarily be approximate, and quadrupole effects can be safely neglected in our current simulations without substantially changing our conclusions.…”

One-Electron Oxidation of Heterodinuclear Organometallic Compounds Having Polyphosphido Bridges

“…The hyperfine splitting from 181 Ta is prominent because this nucleus has a rather large nuclear g factor. 21 The lack of a fully resolved glassy spectrum of 2 + (Figure 2), along with the possible role of quadrupole effects such as those found in other third-row-metal radicals, 22 precludes an analysis of the Ta hyperfine splittings sufficient to give a detailed orbital assignment.…”