Hydrogen‐bonding effects on electronic g‐tensors of semiquinone anion radicals: Relativistic density functional investigation

We report results of systematic g ‐tensor calculations of hydrogen‐bonded complexes of two benchmark semiquinone anion radicals, 1,4 ‐benzoquinone and tetramethyl‐ 1,4 ‐benzoquinone (duroquinone), with water and methanol molecules. The calculations have been carried out with the help of a recently developed g ‐tensor module that is based on a relativistic density functional method that takes spin–orbit interaction self‐consistently into account. We demonstrate the applicability of this new computational scheme to describe quantitatively delicate effects of hydrogen bonding on electronic g ‐tensor values. Also, we explored general trends of how g ‐tensors depend on the structure and stoichiometry of hydrogen‐bonded semiquinone complexes. Complexes exhibiting one hydrogen bond per oxygen atom of the quinones with a linear arrangement of the CO … H moieties were shown to feature g‐shifts induced by these hydrogen bonds that are in close agreement with measured electron paramagnetic resonance data. Based on deviations of calculated and measured g‐components, we classify all other model complexes studied as less probable under the experimental conditions.