Construction of Acylamide-functionalized MOFs for efficient catalysis on the conversion of CO2

By employing a C-3-symmetric ligand, 3,3 ',3 ''-[1,3,5-benzenetriyltris-(carbonylimino)]tris-benzoic acid (H3L), three metal-organic frameworks formulated as {Na-4[Zn-3(L)(2)(mu(3)-OH)(mu(2)-OH)(3)]center dot 3DMF}(n) (1), {[Ca-2(L) (MeOH)(2)(DMF)(3)]center dot Cl}(n) (2) and [Sr-2(L)(H2O)(2)(DMF)Cl]n (3) have been solvothermally synthesized and structur-ally characterized by IR, PXRD and X-ray single crystal diffraction analyses. Complex 1 features a 2D twofold interpenetrated structure in which the [Zn-3(mu(3)-OH)(mu(2)-OH)(3)(CO2)(3)O-3] subunit acts as a 6-connected node and the L-3-ligand as a 3-connected node, exhibiting a binodal (3, 6)-connected topology with a {4(3)}(2){4(3).6(12)} point symbol. Complex 2 shows a 2D double-layered structure, exhibiting a (3,6)-connected {4(3)}(2){4(6).6(6).8(3)} topology based on a centrosymmetric tetranuclear [Ca-4(CO2)(6)] subunit as a 6-connected node and the L-3-ligand as a 3-connected node. Complex 3 exhibits an extended 3D framework with a {4(6)}(2){4(12).6(12).8(4)} topology in which the centrosymmetric {Sr-4(CO2)(6) [(O boolean AND O)acylamide](2)} subunit performs as an eight connected node and the L-3-ligand as an unusual 4-connected node. Complex 1 is explored well as a catalyst for the cycloaddition reaction of CO2 with epoxides into cyclic carbonates under the reaction conditions of 70 degrees C, 1 bar atmosphere and free solvent. The efficient catalytic ability of 1 perhaps attributes to the high density of Lewis acidic sites of Zn2+ and Lewis basic -NH-groups in 1. Beside the basic function, the -NH-group in 1 can also perform as hydrogen bond donor (HBD) for the activation of epoxide in the catalytic process. A plausible mechanism for synergistic catalysis is proposed for the cycloaddition reaction.