Tunable CO₂ Capture and Release Using Redox-Switchable Carboranes

Area of Science:

• Materials Science
• Inorganic Chemistry
• Supramolecular Chemistry

Background:

• Carbon dioxide (CO2) capture and utilization are critical for mitigating climate change.
• Development of efficient and tunable materials for reversible CO2 capture remains a significant challenge.
• Carboranes offer unique structural and electronic properties for potential applications in gas capture.

Purpose of the Study:

• To synthesize and characterize redox-switchable carboranes for tunable CO2 capture.
• To investigate the mechanism of CO2 interaction with different carborane species.
• To evaluate the reversibility of CO2 capture and the tunability of binding constants.

Main Methods:

• Synthesis of substituted 1-PR2-2-BR'2-ortho-carboranes with varying Lewis acid/base strengths.
• Redox-induced transformation of carboranes from closo to reactive nido forms using KC8.
• Spectroscopic and crystallographic analysis of CO2-bound carborane complexes.
• Determination of CO2 binding constants with alkali metal cations.

Main Results:

• Two carborane derivatives, Ph/CyCb and tBu/C6F5Cb, were synthesized and reduced to reactive nido species.
• The nido-Ph/CyCb species captured and reduced CO2 to a formate adduct.
• The nido-tBu/C6F5Cb species weakly captured CO2, forming a P-CO2-K+ adduct, tunable with alkali metal cations (Li+, Na+, K+).
• CO2 release was achieved via chemical oxidation, and binding constants varied significantly with cation choice (log K: 5.5 for Li+, 3.4 for K+).

Conclusions:

• Redox-switchable carboranes provide a versatile platform for reversible CO2 capture.
• The ability to tune CO2 binding constants through alkali metal cation selection is demonstrated.
• These findings present a novel approach for redox-controlled CO2 capture and release systems.