Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear Mn2II,III complex

Simulation of X- and Q-band electron paramagnetic resonance (EPR) spectra of an unsymmetric dinuclear [Mn2II,IIIL(μ-OAc)2]ClO4 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 MnIII ion is a result of the Jahn-Teller effect and thus an inherent character. In contrast, the anomalous hyperfine anisotropy of the MnII ion is attributed as being transferred from the MnIII ion through the spin exchange interaction. The anisotropy parameter for the MnII is deduced as DII = −1.26 ± 0.2 cm−1. This is the first reported DII value for a MnII ion in a weakly exchange coupled mixed-valence Mn2II,III complex with a bis-μ-acetato-bridge. The dxy1dyz1dzx1dx2-y21 electronic configuration of the MnIII ion in 1 is revealed by the negative sign of its intrinsic hyperfine tensor anisotropy, ΔaIII = az − ax,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.