Construction of (3,6)-connected polyoxometalate-based metal–organic frameworks (POMOFs) from triangular carboxylate and dimerized Zn4-ε-Keggin†
Abstract
Using the methodology of extension of reduced transition metal-grafted ε-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]·0.5H2O (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 Zn4-{ε-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 (4·85)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.