COORDINATION GEOMETRY OF THE COPPER-PYRIDINE COMPLEX IN FROZEN SOLUTION AS STUDIED BY PROTON AND DEUTERIUM 2-DIMENSIONAL HYPERFINE SUBLEVELCORRELATION ELECTRON-SPIN-RESONANCE SPECTROSCOPY

The coordination geometry of the tetrapyridine-copper(II) complex in f rozen solution is investigated by proton and deuterium two-dimensional hyperfine sublevel correlation spectroscopy (HYSCORE) electron spin r esonance experiments. In particular, the deuterium experiment demonstr ates the potential of this method, which lies in the superior spectral resolution of the two-dimensional spectra. This allows us to resolve deuterium nuclear quadrupole splittings of the cross peak ridges even in orientationally disordered systems, which in turn yield structural information about the overall complex symmetry. Proton and deuterium e xperiments show pronounced cross peak ridges from protons and deuteriu ms at the C2 and C6 carbon atoms of the pyridine molecule. The coordin ation geometry within the complexes could be deduced from orientation- selective deuterium spectra. Severe deviations from the D-4h complex s ymmetry were found in such a way that the pyridine molecules are arran ged with their molecular mirror plane perpendicular to the complex pla ne. The complex geometry experiences a significant variance with respe ct to the Cu-N bond directions due to random spatial constraints induc ed by solvent molecules.