Syntheses, Structures, and Photoluminescence of Four d¹⁰ Metal−Organic Frameworks Constructed from 3,5-Bis-oxyacetate-benzoic Acid

A new multicarboxylate ligand, 3,5-bis-oxyacetate-benzoic acid (H3BOABA), was designed and introduced to construct novel metal−organic framework materials with potential luminescent properties. Four complexes, Zn2(BOABA)(OH)·H2O (1), Zn4(BOABA)2(4,4′-bipy)2(OH)2·H2O·0.5CH3CH2OH (2), Cd3(BOABA)2(H2O)6·6H2O (3), and Cd4(BOABA)2(phen)4(OH)2·H2O (4), were synthesized hydrothermally and characterized. 1 features an unusual 5-connected 46.64 uninodal net with both the dinuclear Zn(II) unit and the BOABA ligand being the square pyramidal nodes. 2 presents an interesting three-dimensional (3,8)-connected network constructed from pillared undulate layers, which shows large one-dimensional channels with dimension of 11.97 × 13.82 Å along the a axis. The self-assembly between the Cd(II) ions and the BOABA ligand leads to a bilayer motif 3, whereas the presence of the auxiliary phen ligand results in a new compound 4 with monolayer construction based on tetranuclear [Cd4(OH)2]6+ clusters. Photoluminescence studies reveal that these four complexes exhibit strong fluorescent emission bands in the solid state at room temperature. The theoretic calculations show that four complexes are indirect band gap semiconductors and the fluorescent emission peaks could be attributed to the ligand−ligand charge transfer. The thermal stabilities of these complexes were also examined.