Synthesis and photo-/electro-catalytic properties of Keggin polyoxometalate inorganic–organic hybrid layers based on d10 metal and rigid benzo-diazole/-triazole ligands

Abstract

Herein, five Keggin polyanion-templated inorganic–organic hybrids, (H₃biz)₄[SiMo₁₂O₄₀] (1), (H₃biz)₃(H₂biz)[PMo₁₂O₄₀] (2), [{Cu₇(Hbtz)₂(btz)₄}{PMo₁₂O₄₀}] (3), [{Ag₇(Hbtz)₂(btz)₄}{AsW₁₂O₄₀}] (4), and [{Ag₉(H₂biz)₂(biz)₄} {H₂PW₁₂O₄₀}] (5) (H₂biz = benzimidazole, Hbtz = benzotriazole) were hydrothermally synthesized and characterized via elemental analysis, thermogravimetry (TG), infrared spectroscopy (IR), ultraviolet spectroscopy (UV), and single-crystal X-ray diffraction. A remarkable aspect of compound 1 is that six pairs of H₂biz ligands are circularly arranged around the {SiMo₁₂} cluster; this leads to the formation of a unique 2-D supramolecular layer. The most prominent feature of the structure of compound 2 is that protonated Hbiz ligands link the {PMo₁₂} cluster into hexagonal units, which are further extended into a 2-D supramolecular array via edge-sharing modes. The Keggin {PMo₁₂} and {AsW₁₂} clusters in compound 3 and 4 are first extended into octa-connected 2-D sheets by the unusual heptanuclear complex {M₇(Hbtz)₂(btz)₄} (M = Cu for 3 and Ag for 4) linker. Interestingly, two types of M–M interactions exist in the heptanuclear units. Compound 5 exhibits an unprecedented 2D network constructed from nine-nuclear silver complex {Ag₉(biz)₄(H₃biz)₂} bridges and {PW₁₂} clusters. Most strikingly, carbene silver and the coexistence of multiple Ag–C bonds are first observed in the nine-nuclear unit. Intensive Cu^I/Ag^I–π interactions and π–π stacking play important roles in the packing arrangements of 3–5. Additionally, the electrochemical, electrocatalytic, fluorescence, and photocatalytic properties of 1–5 have been investigated in detail.