Indium–Organic Frameworks Based on Dual Secondary Building Units Featuring Halogen-Decorated Channels for Highly Effective CO₂ Fixation

Abstract

With the utilization of a "bifunctional liganddirected strategy", three isostructural indium−organic frameworks based on dual secondary building units (SBUs) were successfully constructed with targeted structures. In their frameworks, two types of unsaturated monomeric indium SBUs[In(OOC-) 2 (-N-)X(H 2 O)] and [In(OOC-) 2 (-N-)X 2 ] − (X = Cl, Br, and I)assemble to form 1D tubular channels with both open metal sites and weak base polarizing substituents. The trimeric indium SBUs [In 3 O(OOC-) 6 (DMA) 3 ] + serve as robust external linkers to extend into a 3D honeycomb double-walled framework with nanoscale channels. By changing the polarizing substituents in situ with different halogens (Cl − , Br − , and I − ), three obtained isostructural MOFs show different channel characteristics, such as alkalinity of the polarizing substituents, acidity of the polarized open indium sites, extended channel sizes, and increased pore volumes (from -I to -Cl). Subsequently, we took the three MOFs collectively as a platform to investigate the impact of the different coordinated halide ions on channel functions, especially on CO 2 adsorption and chemical conversion. Accordingly, the three nanochannel MOF catalysts exhibited highly effective performances in catalyzing cycloaddition of CO 2 with large-sized epoxides, particularly styrene oxide, into value-added productsstyrene carbonates with yields of 91−93% and high selectivity of 95−98%under mild conditions. We speculated that the superior catalytic efficiencies of the three MOF catalysts could be ascribed to the synergistic effect of open indium sites as Lewis acid with different halide ions as weak base sites, which might enhance the catalytic selectivity through polarizing and activating CO 2 molecules during the reaction process.

Rational Stepwise Construction of Different Heterometallic–Organic Frameworks (HMOFs) for Highly Efficient CO2 Conversion

“…As chematic illustration for the CO 2 cycloaddition reactioni sp resented in Scheme2. [24][25][26][27][28][29] Figure 5. Coordination environment of the Tb III andAg I ions in 4.Symmetry codes:#1: 1Àx, Ày,1 Àz;#2: Àx, À0.5+ +y,0.5Àz;# 3: À1+ +x,0.5Ày, À0.5Àz; #4: x,0.5Ày, À0.5Àz;#5: Àx, Ày, Àz.…”

Ligand Functionalization in Zirconium‐Based Metal‐Organic Frameworks for Enhanced Carbon Dioxide Fixation

“…Based on the structure analysis of F‐NH 2 ‐Zr(H 2 L), CO 2 adsorption results, and previous reports, [ 16–32,53–55 ] the reaction of cycloaddition of CO 2 and SO to form SC is proposed to proceed via a cooperative catalytic mechanism. First, the unsaturated Zr sites and the ‐OH groups, which act as the Lewis acid sites and Brønsted acid sites, coordinate with the O atoms of SO, thus polarizing the ring of SO.…”

“…In recent years, metal‐organic frameworks (MOFs), which possess designable architectures and decorative pore surface, have attracted widespread attention for being applied as heterogenous catalysts in CO 2 conversion, especially in cycloaddition of CO 2 to form cyclic carbonates, [ 16–32 ] because many MOFs possess not only a relative high capacity for CO 2 adsorption, but also unsaturated metal sites that can be regarded as the Lewis acidic sites to trigger this cycloaddition reaction. However, due to the reversible nature of coordination bonds, the chemical stability of most MOFs is still inferior which restricts their practicalities in this field.…”

Recent Advances on Metal‐Organic Frameworks in the Conversion of Carbon Dioxide

“…Finally, the corresponding cyclic carbonate and the catalyst were generated by a ring‐closing step (Scheme 10). [ 96‐97 ]…”