Calculation Methods for EPR of the Isolated Ions

The spectral parameters were obtained by fitting the experimental EPR spectra using the WinSim package. In order to determine the hyperfine linewidth, the specific modulation amplitude of the CW detection mode had to be taken into account. To this end, the theoretical spectrum with optimized Lorentzian linewidth was used as a starting point. Then the theoretical spectrum with the same hyperfine parameters but a reduced Lorentzian linewidth was calculated and transformed taking into account the broadening due to the CW modulation technique. The reduced Lorentzian linewidth was varied until the best correlation between experimental and modulation-transformed theoretical spectrum was obtained. 

The increase in linewidth between MePOZ/MePTZ to MePSZ is due to the spin-orbit coupling effect of Se. (In the case of MePTZ, the increased SOC with respect to MePOZ is not manifest in the linewidth, because other relaxation mechanisms dominate). 

Molecular geometries were optimized using Gaussian03 at a DPT B3LYP/6-31G (2d,2p) level of theory using SCI-PCM solvation model (water). Effective core 

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