Pengpeng Sang

A NbO-type copper metal–organic framework decorated with carboxylate groups exhibiting highly selective CO2 adsorption and separation of organic dyes

A porous Cu metal–organic framework (1) based on a pentacarboxylate ligand and paddlewheel SBU was synthesized and structurally characterized. Complex 1 possesses a NbO-type framework with uncoordinated –COO− groups, resulting in its good selectivity for CO2/N2 (36) and CO2/CH4 (12) as well as a large CO2-uptake capacity of 140 cm3 g−1 at 273 K and 1 bar. Grand Canonical Monte Carlo (GCMC) simulations revealed that strong CO2 adsorption sites exist near the open CuII sites and the uncoordinated –COO− groups. Significantly, complex 1 exhibits water resistance and selective adsorption of cationic methylene blue (MB+) in aqueous solution and the adsorbed MB+ can be released in saturated NaCl solution, making it also a promising porous material for charge and pore-size dependent large-molecule capture and separation. The existence of coordinatively unsaturated metal sites as well as the exposed –COO− groups in the framework of 1 is responsible for its selective gas adsorption and dye separation.

The ligand effect on the selective C–H versus C–C bond activation of propane by NiBr+: a theoretical study

Density functional theory has been employed to investigate the ligand effect in the reaction of ligated NiBr+ with propane. Both initial C–H and C–C bond activation mechanisms for losses of HBr, H2, and CH4 are analyzed in terms of the topology of the potential energy surface. Losses of HBr and H2 involve three C–H activation mechanisms, that is, α,β-H, α,γ-H, and β,α-H abstractions, where the last β,α-H abstraction is the most favorable mechanism. Loss of CH4 involves initial C–C activation, but it is prevented by the high-energy barrier. When propane reacts with the open-shell ligated NiBr+, the ligand of Br in the initial C–H activation could direct abstract a H atom from propane substrate via a four-center transition state, without forming multi-σ-type bonding of Ni+, whereas the metal center in the initial C–C activation needs to experience an unfavorable three σ-type bonding (with Br, CH3, and CH2CH3), which explains why HBr and H2 are formed in the reaction of BrNi+/C3H8 and CH4 not.