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Abstract

In this work, we report on a detailed high-field EPR investigation of magnetic parameters of deuterated nitroxide radicals dissolved in deuterated frozen solvents of polar or unpolar, protic or aprotic character including ortho-terphenyl, methanol, propanol, glycerol, aniline, phenol, and water. The analysis of the high-resolution W-band (95GHz) pulsed ELDOR-detected NMR (EDNMR) and 244GHz cw EPR spectra yielded precise electron Zeeman, g(xx), N-14 hyperfine, A(zz), and N-14 quadrupole, P-zz, tensor components, which are most sensitive probes for the microenvironment of dissolved nitroxide radicals. Remarkable changes in the solvation networks were foundin the various matrices. The solvent-dependent magnetic parameters of the nitroxide are discussed on the basis of previous semi-empirical and DFT quantum chemical calculations in an attempt to adequately model the nitroxide-matrix interactions. The obtained results demonstrate that the principal values of all the magnetic interaction parameters primarily depend on the nitroxide hydrogen-bond situation and the type of hydrogen-bond donor group of the solvent. The solvent bulk polarity, as described by the static dielectric constant, is of minor importance.