Multivariate metal-organic framework MTV-MIL-101 via post-synthetic cation exchange: is it truly achievable?

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Post-synthetic exchange (PSE) is a method for modifying metal-organic frameworks (MOFs).
• Solvent-assisted cation substitution (SACS) is used for mixed-metal multivariate MOFs (MTV-MOFs).
• Previous reports on mixed-metal MIL-101 via PSE have been debated, with direct synthesis considered the only viable route by some.

Purpose of the Study:

• To settle the dispute regarding the synthesis of mixed-metal MIL-101 using PSE.
• To investigate the validity of previously reported PSE methods for MIL-101.
• To establish optimized conditions for achieving mixed-metal MIL-101 via PSE.

Main Methods:

• Investigated Szilágyi's PSE method under extended time and varying metal precursors.
• Re-evaluated the refluxing solvent, switching from water to dimethylformamide (DMF).
• Optimized reaction conditions, including temperature (110 °C) and time (20 h).

Main Results:

• Initial attempts to replicate Szilágyi's method under extended conditions and with different precursors were unsuccessful.
• By modifying the refluxing solvent to DMF and adjusting reaction conditions (110 °C, 20 h), mixed-metal MIL-101(Cr/Fe) was successfully synthesized.
• This demonstrates that PSE is a viable method for producing mixed-metal MIL-101.

Conclusions:

• The direct synthesis is not the only method for obtaining mixed-metal MIL-101.
• Optimized PSE conditions, specifically using DMF as the solvent and prolonged reaction times at elevated temperatures, enable the successful synthesis of mixed-metal MIL-101(Cr/Fe).
• This work clarifies the synthetic accessibility of mixed-metal MIL-101 frameworks through PSE, resolving prior scientific debate.