Catalytic CO₂ Fixation over a Robust Lactam-Functionalized Cu(II) Metal Organic Framework

A porous, Cu(II)-metal organic framework (Cu-MOF) constituted of a rigid lactam functionalized ditopic ligand (H₂L) was synthesized at room temperature under slow evaporation conditions {H₂L = (5-(1-oxo-2,3-dihydro-1H-inden-2-yl)isophthalic acid)}. The single crystal X-ray structure revealed the formation of a 3D framework of Cu-MOF with one-dimensional (1D) channels decorated with lactam groups and exposed metal centers in the crystallographic c-axis. Interestingly, Cu(II) coordinated DMF molecules were eliminated from the Cu(II) metal center on activation of Cu-MOF at a temperature of 150 °C under high vacuum to generate a solvent free framework with pores lined with unsaturated Lewis acidic Cu(II) ions, i.e., Cu-MOF'. The lactam functionalized channels inclined toward the CO₂, which interact with the Cu(II) metal sites lined in the channels of Cu-MOF' and exhibit fascinating solvent-free heterogeneous catalytic conversion of CO₂ to cyclic carbonates at atmospheric pressure of CO₂, under mild conditions. Furthermore, the Cu-MOF' catalyst was easily recycled and reused for several cycles without a significant loss in catalytic activity.