A new porous MOF with two uncommon metal-carboxylate-pyrazolate clusters and high CO2/N2 selectivity

By a less-exploited strategy, a stable framework was constructed by using 4,4'-biphenyldicarboxylic acid (H2bpdc) and methyl-functionalized 3,3',5,5'-tetramethyl-4,4'-bipyrazole (H2bpz) coligands, revealing a new (6,8)-connected net based on two extremely rare trinuclear and tetranuclear metal-carboxylate-pyrazolate clusters. The framework is very porous and possesses not only high CO2 loadings but also very high CO2/N2 selectivities at 308 and 313 K because of the polar pore surface decorated by clusters, pyrazolyl units, and confined cages with methyl groups dangling. Importantly, GCMC simulation identified two favorable CO2 sorption sites located sequentially near Co3(pz)3 and Co3(CO2)2(pz) motifs of the tetranuclear cluster, and the multipoint framework-CO2 interactions were distinguished. The framework also displays remarkable stability toward water and organic solvents.