Construction of (3,6)-connected polyoxometalate-based metal-organic frameworks (POMOFs) from triangular carboxylate and dimerized Zn 4 -ε-Keggin.

Using the methodology of extension of reduced transition metal-grafted ε-Keggin polyoxoanions with two types of terphenyl-based tricarboxylates of H3 L1 (3,5',3''-position substitution) and H3 L2 (4,5',4''-position substitution) we isolated two (3,6)-connected 3D polyoxometalate-based metal-organic frameworks, [TBA]3 [H3 PMo12 O40 ][Zn4 L2 ] (1, YZU-105), and [TPA]3 [H3 PMo12 O40 ][Zn4 L1 ]·0.5H2 O (2, YZU-106) (H3 L1 = [1,1';3',1''-terphenyl]-3,5',3''-tricarboxylic acid; H3 L2 = [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 Zn4 -{ε-H3 PMo12 O40 }. 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 (4·85 )3 (4·82 )6 and (65 ·10)3 (63 )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.