Spin-crossover in an iron(III)-bispidine-alkylperoxide system

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Spectroscopy

Background:

• Bispidine ligands offer unique coordination environments for metal ions.
• Iron complexes with peroxide ligands are crucial in bioinorganic chemistry and catalysis.
• Spin-crossover phenomena in iron complexes are sensitive to ligand field and external stimuli.

Purpose of the Study:

• To synthesize and characterize a novel iron(III) tert-butylperoxo complex using a tetradentate bispidine ligand.
• To investigate the spin-crossover properties of the complex as a function of solvent.
• To correlate experimental spectroscopic data with theoretical calculations.

Main Methods:

• Synthesis of the iron(II) bispidine complex.
• Oxidation to the iron(III) tert-butylperoxo complex using tert-butyl hydroperoxide.
• Characterization using UV-vis, resonance Raman, and Electron Paramagnetic Resonance (EPR) spectroscopy.
• Density Functional Theory (DFT) calculations for vibrational analysis.

Main Results:

• Formation of the end-on tert-butylperoxo iron(III) complex [Fe(III)(L)(OOtBu)(X)]n+.
• Demonstration of spin-crossover behavior influenced by solvent and counter-anions.
• Experimental Raman vibrations for both low-spin and high-spin isomers were observed.
• Good agreement between experimental and DFT-computed Raman spectra.

Conclusions:

• The synthesized iron(III) complex with a bispidine ligand is a spin-crossover compound.
• Solvent and anion identity play a critical role in tuning the spin state.
• DFT calculations effectively model the vibrational properties of different spin states.