Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear [formula omitted] complex

Abstract

Simulation of X- and Q-band electron paramagnetic resonance (EPR) spectra of an unsymmetric dinuclear [ Mn 2 II , III L ( μ - OAc ) 2 ] ClO 4 complex ( 1), (L is the dianion of 2-{[ N, N-bis(2-pyridylmethyl)amino]methyl}-6-{[ N-(3,5-di- tert-butyl-2-hydroxybenzyl)- N-(2-pyridylmethyl)amino]methyl}-4-methylphenol) was performed using one consistent set of simulation parameters. Rhombic g-tensors and hyperfine tensors were necessary to obtain satisfactory simulation of the EPR spectra. The anisotropy of the effective hyperfine tensors of each individual 55Mn ion was further analyzed in terms of intrinsic hyperfine tensors. Detailed analysis shows that the hyperfine anisotropy of the Mn III ion is a result of the Jahn-Teller effect and thus an inherent character. In contrast, the anomalous hyperfine anisotropy of the Mn II ion is attributed as being transferred from the Mn III ion through the spin exchange interaction. The anisotropy parameter for the Mn II is deduced as D II = −1.26 ± 0.2 cm −1. This is the first reported D II value for a Mn II ion in a weakly exchange coupled mixed-valence Mn 2 II , III complex with a bis-μ-acetato-bridge. The d xy 1 d yz 1 d zx 1 d x 2 - y 2 1 electronic configuration of the Mn III ion in 1 is revealed by the negative sign of its intrinsic hyperfine tensor anisotropy, Δ a III = a z − a x, y = −46 cm −1. Lower spectral resolution of the Q-band EPR spectrum as compared to the X-band EPR spectrum is associated to large line width broadening of the x- and y-components in contrast to the z-component. The origins of the unequal distribution of line width between the z- and x-, y-components are discussed.