Bifunctional 3D Cu-MOFs containing glutarates and bipyridyl ligands: Selective CO₂ sorption and heterogeneous catalysis

We report bifunctional three-dimensional (3D) Cu-MOFs with high selectivity of CO₂ over N₂ and H₂ as well as high catalytic activity for transesterification of esters. The Cu-MOFs containing Cu₂ dinuclear units connected by glutarates and bipyridyl ligands are formulated as [{Cu₂(Glu)₂(μ-bpa)}·(CH ₃CN)]_n (1) and [{Cu₂(Glu)₂(μ-bpp) }·(C₃H₆O)]_n (2) (Glu = glutarate, bpa = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4-pyridyl)propane). These two new bifunctional 3D Cu-MOFs possess very similar pore shape with different pore dimensions. Their gas sorption behaviors were investigated by using CO ₂, N₂ and H₂ at suitable temperatures. Both MOFs exhibited good CO₂ selectivity over N₂ and H ₂. MOF 1 having a smaller pore dimension exhibited much higher CO₂ adsorption enthalpy than MOF 2 having a larger pore dimension. However, MOF 2 exhibited more enhanced CO₂ uptake ability than MOF 1. A subtle variation of pore dimension indeed influenced the CO₂ uptake ability somewhat significantly especially at higher temperatures such as 273 K and 298 K. Heterogeneous catalytic activities of the MOFs were also investigated in detail. Only MOF 1 appeared to be an efficient, mild, and easily recyclable heterogeneous catalyst for the transesterification of esters and constitutes a promising class of heterogeneous catalysts that allowed reuse without a significant loss of activity through twenty runs with ester.