Endohedral Functionalization for Structural Transformation of Polyoxovanadate-Based Metal-Organic Cube

Functionalized internal modifications of metal-organic polyhedra (MOPs) can endow properties and functions different from the original ones. Until now, there have been only a few examples of endohedral modifications of polyoxovanadate-based MOPs. Herein, an efficient coordination-driven strategy was chosen for the inner modification of two metal-organic cubes (MOCs) with different sizes, VMOC-1 and VMOC-4, constructed from polyoxovanadate clusters [V₆O₆(OCH₃)₉(SO₄)(CO₂)₃]^2- SBU and tetradentate ligands. Pyridinophosphonic acid with potential coordination capability was introduced to replace the sulfate of the hexavanadate cluster and graft the pyridine functional group inside the cage. The introduction of pyridylphosphate in the VMOC-4 system gave a cubic cage with a pyridyl endo-modified isomer. Interestingly, the smaller cubic cage VMOC-1 was induced to undergo structural transformation to obtain VMOC-py-1. The organic dyes adsorption of VMOC-py-1 and VMOC-1 showed that the endomodified structure could adsorb larger and more dyes, compared to the original cube.