Construction and in-cage modification of metal-organic polyhedra based on Anderson-like polyoxovanadate clusters

Two tetrahedral metal-organic polyhedra (MOPs) constructed from Anderson-like alkoxo-polyoxovanadate clusters, [NH2Me2]8{[V6O6(OCH3)9(SO4)]4(2,6-NDC)6}(MeOH)15(DMA)9 (1) and [NH2Me2]8{[V6O6(OCH3)9(C6H5PO3)]4(2,6-NDC)6}(MeOH)9(DMA)10 (2), were synthesized under solvothermal conditions. They are isomorphic tetrahedra composed of 3-connected [V6O6(OCH3)9(X)] SBUs and rigid bidentate ligand 2,6-naphthalenedicarboxylic acid (NDC). The difference between the two structures is modification of the inner cage in 2 by introduction of phenylphosphonic acid. The space inside the molecular cage was reduced from 1100 Å3 to 700 Å3 after introduction of phenylphosphonic acid, as calculated by the VIODOO program. Interestingly, the iodine adsorption performance of 2 was improved by more than three times compared to 1 after the introduction of phenylphosphonic acid. These findings may provide new insights into the modification and functionalization within the cage of MOPs.