The iron(II) complex of a tetradentate bispidine ligand with two tertiary amines and two pyridine groups ( L) dimethyl [3,7-dimethyl-9,9'-dihydroxy-2,4-di-(2-pyridyl)-3,7-diazabicyclo nonan-1,5-dicaboxylate]) is oxidized with tertbutyl hydroperoxide to the corresponding end-on tert-butylperoxo complex [Fe-III(L)((OOBu)-Bu-t)(X)](n+) (X) solvent, anion). UV-vis, resonance Raman, and EPR spectroscopy, as a function of the solvent, show that this is a spin-crossover compound. The experimentally observed Raman vibrations for both low-spin and high-spin isomers are in good agreement with those computed by DFT.