Gas-Phase Characterization of Redox-Active Manganese Complexes

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Mass Spectrometry

Background:

• Manganese complexes exhibit diverse redox chemistry, often involving structural changes and ligand dynamics.
• The 2,6-diguanidylpyridine (dgpy) ligand stabilizes manganese in +II, +III, and +IV oxidation states in condensed phase complexes.
• The manganese(IV) complex is a potent oxidant in solution.

Purpose of the Study:

• To investigate the gas-phase stability and redox behavior of manganese-dgpy complexes with hexafluorophosphate counterions.
• To compare gas-phase properties with known condensed-phase behavior.
• To elucidate the reactivity of manganese complexes with triethylamine in the gas phase.

Main Methods:

• Utilized two modified 3D Paul ion trap mass spectrometers for gas-phase ion analysis.
• Employed collision-induced dissociation (CID) and UV/vis photodissociation to assess stability.
• Recorded gas-phase UV/vis spectra and studied reactions with triethylamine.

Main Results:

• Observed six cationic species of [Mn^x(dgpy)₂(PF₆)_y]ⁿ⁺ across Mn(II), Mn(III), and Mn(IV) oxidation states, including a reduced dgpy ligand complex.
• Mn(II) species demonstrated the highest stability under dissociation experiments.
• Gas-phase UV/vis spectra mirrored condensed-phase features, with variations in relative band intensities.
• The Mn(IV) complex oxidized triethylamine to Mn(III), while Mn(III) showed limited reactivity.

Conclusions:

• Gas-phase studies provide insights into the intrinsic stability and redox properties of manganese-dgpy complexes.
• Stability is influenced by oxidation state and the presence of counterions, with Mn(II) being the most robust.
• The observed gas-phase reactivity of Mn(IV) with triethylamine aligns with its strong oxidizing nature.