Two ligand-functionalized Pb(II) metal-organic frameworks: structures and catalytic performances

A microporous Pb(II) metal-organic framework (MOF) [PbL2]center dot 2DMF center dot 6H(2)O (1) has been assembled from a N-oxide and amide doubly functionalized ligand HL (= N-(4-carboxyphenyl)isonicotinamide 1-oxide). Complex 1 features a three-dimensional (3D) framework possessing one-dimensional (1D) rhombic channels with dimensions of 13 x 13 angstrom(2). The 3D framework is built up from 1D PbO2 chains that link ligands in parallel fashion to construct single-wall channels. When recrystallizing 1 in a DMSO-DMF mixture (3 : 5 v/v), a new coordination polymer, [PbL2]center dot DMF center dot 2H(2)O (2), was obtained. Complex 2 is also a 3D framework containing 1D rectangular channels, but the channel dimensions become reduced in size to 13 x 8 angstrom(2) due to reorganization of the Pb(II) coordination environment. The PbO2 chains in 2 are reformed to link ligands in a double-wall fashion, significantly reducing the channel size. Even though, the guest exchange study indicates that the DMF molecules in 2 could be replaced with benzene molecules when immersing in benzene solvent, showing single-crystal-to-single-crystal (SC-SC) guest exchange in the solid state and leading to a daughter crystal [PbL2]center dot 0.5C(6)H(6)center dot 2H(2)O (2'). Desolvated 1 and 2 display preferential adsorption behaviors of water vapour over CO2 due to the hydrophilic nature of the channels and the strong host-guest interactions. Catalytic tests indicate that desolvated 1 and 2 have size-selective catalytic activity towards the Knoevenagel condensation reaction.