The structure of a model system representing SMM was derived from the original one by replacing the mesitylene groups in the chelating ligand, tpa Mes , by hydrogenes. We refer to the resulting ligand as tris(pyrrolylmethyl)amine (tpa). The ground state of the neutral (tpa)Fe has 5 unpaired electrons, as in Fe 3+ ion. The geometry of the neutral (tpa)Fe complex was optimized with ωB97X-D/cc-pVDZ for the hextet state. We used this geometry for the calculations of the anion as well.