The effect of protonation on [Mn(IV)(μ2-O)] 2 complexes

Area of Science:

• Inorganic Chemistry
• Bioinorganic Chemistry
• Oxidation Catalysis

Background:

• Manganese-oxo clusters are crucial in biological systems, particularly in oxygen evolution.
• Understanding their redox properties is key to elucidating enzymatic mechanisms.
• The [Mn2O2](4+) core is a fundamental structural motif in these clusters.

Purpose of the Study:

• To synthesize and characterize a series of [Mn(IV)(X-SALPN)(μ2-O)]2 complexes.
• To investigate the protonation behavior of these complexes and its effect on redox potentials.
• To explore the implications for enzymatic control of manganese oxidation states.

Main Methods:

• Synthesis of manganese complexes with varying X-SALPN ligands.
• Spectroscopic and electrochemical characterization.
• Titration studies to determine pKa values and redox potentials.

Main Results:

• The [Mn2O2](4+) core exhibits protonation to form [Mn(IV)(X-SALPN)(μ2-O,OH)]2 (+).
• A linear correlation was observed between pKa values and redox potential shifts (84 mV/pKa).
• The [Mn2O2](4+) core acts as a unit where protonation energy relates to Mn(IV) reduction.

Conclusions:

• Protonation significantly influences the redox properties of manganese-oxo clusters.
• This sensitivity provides a potential mechanism for enzymatic regulation of oxidizing capacity.
• The findings contribute to understanding the function of manganese clusters in biological catalysis.