Unique T-Shaped Ligand as a New Platform for Metal-Organic Frameworks

The utilization of a rationally designed T-shaped ligand 4,4',4 ''-(1H-benzo[d]imidazole-2,4,7-triyl)tribenzoic acid (H(3)BTBA) as the platform for constructing metal-organic frameworks (MOFs) with structure diversity was achieved. Five new MOFs, [Zn4O(BTBA)(2)] (BUT-34), [Fe2CoO(BTBA)(2)(H2O)(3)] (BUT-35), [Cu-9(BTBA)(4)(H2O)-(DMA)] (BUT-36), [Eu-2(HBTBA)(2)(OH)(2)(H2O)(6)] (BUT-37), and [In(BTBA)(DMF)] (BUT-38) (BUT = Beijing University of Technology), have been solvothermally synthesized and structurally characterized. Combining with several popularly used metal-cluster secondary building units, the five MOFs show novel structural features. BUT-34 with typical tetranuclear Zn4O clusters shows three-dimensional (3D) networks with a new (3,6)-connected topology. BUT-35 exhibits a (3,6)-connected flu-3 network with trinuclear [Fe2Co(mu(3)-O)] clusters. BUT-36 represents a mixed Cu(II)/Cu(I) based 3D framework, in which the T-shaped ligand adopts different coordination modes. However, BUT-37 and -38 consist of binuclear Eu-2 paddle-wheel clusters and single In(III) ions with two-dimensional layer structures, respectively. Clearly, the structural diversity of these MOFs can be attributed to the unique structure and variable coordination patterns of the T-shaped ligand. This work thus enriches the in the structural design based on the low-symmetric ligands, and thereby function exploration.