An irregular-octagonal-prism-shaped host–guest supramolecular network based on silicotungstate and manganese-complex for light-driven hydrogen evolution

Abstract

A new polyoxometelate (POM)-based host–guest supramolecular network, [Mn^II(L)₃]₂(SiW₁₂O₄₀)·4H₂O (L = 3-pyraziny-1,2,4-triazole), was synthesized by the hydrothermal reaction, and characterized by single crystal X-ray diffraction, infrared spectroscopy, powder X-ray diffraction and solid-state ultraviolet visible diffuse reflection. The compound is composed of Keggin type [SiW₁₂O₄₀]²⁻ anion (SiW₁₂) and manganese–L complex. A structural feature for the compound is that the manganese–L complexes are arranged to construct a host–guest network with two types of channels (the small and big ones), and the [SiW₁₂O₄₀]²⁻ as guests are only encapsulated in holes of the big channels. The whole network is still highly open due to possessing vacant channels and therefore H₂O and H⁺ can diffuse through these vacant channels with ease. Hence, it is a favourite for imposing more photo-active sites ([SiW₁₂O₄₀]²⁻ and Mn) for H₂O and H⁺. Consequently, the photocatalytic hydrogen productivity of the title compound can reach 337.76 μmol⁻¹ g⁻¹ h⁻¹, which is much higher than the 6.31 μmol g⁻¹ h⁻¹ of its parent (TBA)₄SiW₁₂O₄₀ POM under identical experimental conditions.