Two new Zn2+/Cd2+ Metal-Organic Frameworks (MOFs) constructed from asymmetrical tricarboxylic acid ligands

Abstract

Two new Metal-Organic Frameworks (MOFs), namely, [Cd(HL1)(H2O)] 1, [H2(bpp)][Zn2(L2)2(bpe)]·2H2O 2 (H3L1 = 4-(5-carboxy-pyridine-3-yloxy)-phthalic acid, H3L2 = 3-(4-carboxy-phenoxy)-phthalic acid, bpe = 1,2-bis(4-pyridyl) ethylene, bpp = 1,3-bis(4-piperidyl) propane) have been isolated employing two V-shaped asymmetric tricarboxylic acid ligands under hydrothermal conditions. X-ray single-crystal diffraction analysis reveals that μ4-mode HL12− molecules propagate the Cd2+ centers into a 3-D network with point symbol of 66 for 1. One-dimensional channels are observed in 1, but because of 2-fold interpenetration phenomenon, these channels become small or disappear. 2 possesses a 2-D layered structure with (3, 4)-connected (42ˑ63ˑ8) (42ˑ6) topology. The carboxyl moieties for L2 molecules first extend the Zn2+ centers into a 1-D double chain, then via the interactions between Zn2+ and pyridine N atoms, the resulting 1-D double chain are strutted by the rigid bpe ligands to form a 2-D layer framework. It is noteworthy that one-dimensional channels of ca. 13 × 13 Å2 are observed. H2(bpp)2+ and two lattice water molecules occupy the space of the channels. The introduced bpp molecules only serve as the templating agent and are not involved in the formation of this layer network. The photoluminescence properties of 1 and 2 were investigated.