Synthesis, Characterization, and Stability of {Mo₁₃₂}-Type Capsules Containing Phosphorus Oxo Anion Ligands

Area of Science:

• Inorganic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• The {Mo132}-type molecular capsule is a well-known polyoxometalate structure.
• Previous work characterized {Mo132} capsules with hypophosphite and phosphate ligands.
• Ligand exchange reactions are a common method for functionalizing polyoxometalates.

Purpose of the Study:

• To synthesize and characterize new {Mo132}-type molecular capsules with phosphite and methylphosphonate ligands.
• To investigate the stability and potential side reactions of these capsules in solution and solid states.
• To extend the understanding of ligand diversity within the {Mo132} capsule framework.

Main Methods:

• Ligand exchange reactions using acetate-containing {Mo132} precursor.
• Infrared (IR) spectroscopy and X-ray diffraction for initial characterization.
• Nuclear Magnetic Resonance (NMR) spectroscopy (1H and 31P) in D2O for detailed analysis.
• Single-crystal X-ray diffraction for structural elucidation of one complex.

Main Results:

• Successful synthesis of {Mo132} capsules with phosphite and methylphosphonate ligands.
• Characterization confirmed the presence of target ligands and residual acetate in some samples.
• NMR studies revealed framework degradation, releasing {MoO3H}+ units, and slow transformation into Strandberg-type and reduced Keggin-type complexes.
• Single-crystal X-ray diffraction provided detailed structural information for one capsule.

Conclusions:

• The {Mo132} capsule framework can accommodate a wider range of phosphorus oxo anions.
• Side reactions, including framework degradation and structural transformation, occur but are generally limited over short periods.
• NMR spectroscopy is a powerful tool for monitoring the stability and integrity of polyoxometalate capsules in solution.