EPR of High‐Spin Co(II) in Fully‐Chelated Octahedral Environments: From Solid State to Frozen Solution

We present an X‐band EPR and density functional theory (DFT) study of five fully‐chelated Co(II)complexes, in order to assess the differences in their solid state and frozen solution EPR, and to examine the accuracy of the DFT‐predicted EPR parameters. The complexes represent two meridional bis ‐tridentate complexes of bispyrazolylpyridines, and three tris ‐bidentate complexes. Spectra for the meridional complexes show substantial broadening in frozen solution that can be attributed to structural disorder, without significant changes in the magnetic parameters. The two tris ‐bidentate complexes that do not form isomers also give rise to broader spectra in frozen solution, but the features collapse into a more axial pattern, indicating a reduction in E / D . The fifth complex forms three structural isomers, based on the juxtaposition of its pendant groups. DFT was used to predict the spectra of the individual isomers, and produced a sum simulation that reasonably matched its complex solid‐state spectrum. Data are also presented that show the parallel mode response of these systems is unusually strong, and that the ability to observe these signals depends on sublevel mixing, and correlates well with the magnitude of E / D .