Finally, we calculated isotropic hyperfine coupling constants (Aiso) of the above systems to compare to the experimental Mössbauer spectra (see Theoretical Calculations Details). This hyperfine coupling constant is a component of the hyperfine coupling tensor, A, that is used in the spin Hamiltonian formalism to fit EPR and Mössbauer spectra. Resolving the full tensor using the experimental Mössbauer spectra is challenging for the powdered NiPACN samples, instead the fitted internal magnetic field value of 5.4 ± 3T can be converted to a hyperfine coupling constant.