Rhodium Carbonyl Complexes within the Tunable Microenvironments of UiO-66 Analogues

Area of Science:

• Materials Science
• Catalysis
• Coordination Chemistry

Background:

• Metal-Organic Frameworks (MOFs) are promising supports for heterogeneous catalysts.
• Understanding the interaction between metal complexes and MOF active sites is crucial for catalyst design.
• UiO-66 topology MOFs offer tunable microenvironments for supporting catalytic species.

Purpose of the Study:

• To investigate the influence of UiO-66 MOF variants on the chemistry of supported rhodium carbonyl complexes.
• To characterize the Rh carbonyl species formed and their dependence on MOF structure and defects.
• To evaluate the stability and transformation of Rh species under reaction conditions.

Main Methods:

• Synthesis of UiO-66 variants with controlled microenvironments and defect sites.
• Loading of rhodium (Rh) carbonyl complexes onto MOF supports.
• Detailed structural characterization using techniques like defect site analysis.
• Exposure of loaded MOFs to syngas and subsequent analysis of Rh speciation.

Main Results:

• Metal loading is influenced by MOF defect content, metal node type, and linker functional groups.
• Monomeric gem-Rh(CO)₂ and dimeric [Rh₂(μ-Cl)₂(CO)₄] species were identified, with concentrations varying across UiO-66 variants.
• The dimeric Rh species showed moisture sensitivity, and amine-functionalized MOFs prevented its formation.
• Rh in Ce-UiO-66 transformed into a Rh₆(CO)₁₆ cluster upon exposure to syngas.

Conclusions:

• The microenvironment of UiO-66 MOFs significantly impacts the speciation and stability of supported Rh carbonyl complexes.
• MOF defects and functional groups play a critical role in governing metal loading and catalyst behavior.
• UiO-66 topology MOFs exhibit complex behavior as supports, highlighting the need for careful catalyst design for heterogeneous applications.