Metal complexes with varying intramolecular hydrogen bonding networks

Area of Science:

• Coordination Chemistry
• Inorganic Chemistry
• Supramolecular Chemistry

Background:

• Alfred Werner's foundational work distinguished primary and secondary coordination spheres.
• Understanding the secondary coordination sphere's impact is crucial for designing novel metal complexes.

Purpose of the Study:

• To investigate the influence of hydrogen bonding (H-bond) within the secondary coordination sphere on metal complex properties.
• To systematically vary H-bond donor numbers in tripodal ligands to probe their effects on iron(II), manganese(II)-acetato, and manganese(III)-hydroxide complexes.

Main Methods:

• Synthesis of tripodal ligands with varying urea and amidate donors.
• Isolation and characterization of metal complexes using X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy.
• Dioxygen activation for the synthesis of manganese(III)-hydroxide complexes.

Main Results:

• Two iron(II) complexes formed dimers in the solid-state, correlating with increased H-bond donor numbers.
• Dimeric structures of iron(II) complexes were found to persist in acetonitrile solution, as indicated by EPR studies.
• Manganese(II) complexes were isolated as acetato adducts, and a rare manganese(III)-hydroxide complex with an intramolecular H-bond was synthesized.

Conclusions:

• The secondary coordination sphere, particularly H-bonding, significantly impacts metal complex assembly and structure.
• Ligand design incorporating H-bond donors offers a pathway to control the aggregation state of metal complexes.
• The study contributes to the understanding of manganese-oxygen species and H-bonding effects in coordination chemistry.