New types of open-framework vanadium borophosphates with photocatalytic properties

Abstract

The exploration of new open-framework polyoxometalates is very significant in structural chemistry and materials science. Herein, three new organic hybrid three-dimensional vanadium borophosphates (H₃O)₇(H₂aeae)₃{[Cd(H₂O)₃]₂[H₃O⊃(V₂BP₂O₁₂)₆]}·15H₂O (1, aeae = 2-(2-aminoethylamino)ethanol) and (H₃O)₅(H₂aeae)₃{[TM(H₂O)_2.5(H₂aeae)_0.5]₂[H₃O⊃ (V₂BP₂O₁₂)₆]}·9H₂O [TM = Mn(2), Co(3)] were hydrothermally prepared and structurally characterized. The three vanadium borophosphates contain similar 12-member ring crown-shaped clusters [(V₂BP₂O₁₂)₆]¹⁸⁻ based on the linkage of six [V₂O₈] dimers and six [BP₂O₁₀] units. The [(V₂BP₂O₁₂)₆]¹⁸⁻ cluster is further bridged by the unsaturated [Cd(H₂O)₃]²⁺ or [TM(H₂O)_2.5(H₂aeae)_0.5]³⁺ complexes to build new types of open-framework vanadium borophosphates with pores and cavities retained by the protonated H₂aeae²⁺, H₃O⁺ and free H₂O. Surprisingly, the monodentate H₂aeae²⁺ ligand coordinating with a metal center was observed in 2 and 3 for the first time as the aeae molecule acted as the trichelating ligand. Their optical absorption edges were determined to be in the range of 2.61–2.68 eV using solid-state UV-vis spectroscopy. 1–3 exhibited excellent photocatalytic activity towards methylene blue (MB) degradation under visible light irradiation, which presented the first example of organic hybrid open-framework vanadium borophosphates as the photo-catalysts for MB degradation.