Construction of (3,6)-connected polyoxometalate-based metal-organic frameworks (POMOFs) from triangular carboxylate and dimerized Zn4-ε-Keggin

Using the methodology of extension of reduced transition metal-grafted epsilon-Keggin polyoxoanions with two types of terphenyl-based tricarboxylates of H3L1 (3,5 ', 3 ''-position substitution) and H3L2 (4,5 ', 4 ''-position substitution) we isolated two (3,6)-connected 3D polyoxometalate-based metal-organic frameworks, [TBA](3)[H3PMo12O40][Zn4L2] (1, YZU-105), and [TPA](3)[H3PMo12O40][Zn4L1]center dot 0.5H(2)O (2, YZU-106) (H3L1 = [1,1 '; 3 ', 1 ''-terphenyl]-3,5 ', 3 ''-tricarboxylic acid; H3L2 = [1,1 '; 3 ', 1 ''-terphenyl]-4,5 ', 4 ''-tricarboxylic acid; TBA = tetrabutylammonium; TPA = tetrapropylammonium). In both compounds, the building block was the dimerized form of Zn-4-{epsilon-H3PMo12O40}. Such dimerization left six anchoring points for each dimer and, as a result, a 6-connected node was formed. Compounds 1 and 2 exhibited topologies of (4.8(5))(3)(4.8(2)) (6) and (6(5).10)(3)(6(3))(6), respectively. This work illustrates that use of tri-carboxylate substitutions in different positions (3,5 ', 3 ''-position/4,5 ', 4 ''-position) in tripodal terphenyl-based ligands allows different extents of twisting of the peripheral aromatic ring with respect to the central ring, thereby giving rise to different extending directions and symmetries.