High-field pulsed EPR and ENDOR of Gd3+ complexes in glassy solutions

In this work D-band pulsed electron paramagnetic resonance was used to record the field-sweep spectra of several Gd3+ complexes in glassy water-methanol solutions. These spectra were analyzed by a specially developed stochastic superposition model that predicted the essential features of the distribution of the crystal field interaction (CFI) parameters in glassy systems. As a result of this analysis, the CFI distributions for the studied complexes were evaluated. The D-band Mims1H electron-nuclear double resonance spectra were free from CFI-related distortions, which allowed us to accurately determine the hyperfine interaction (HFI) parameters for water ligand protons and to unequivocally establish that the HFI distribution is solely related to the distribution of the Gd−H distances.