Self-assembly of a unique triangle-like tungstovanadate containing pentagonal {(WO₇)W₃(SnR)₂} cluster

In aqueous solution, a novel triangle-like tungstovanadate estertin derivative K₁₀H_10.5[(W₄O₁₅(H₂O)₂){(SnCH₂CH₂COO)₂(V_0.75W_10.75/V_0.25O₃₉)}{{(SnCH₂CH₂COO)₂(μ-OH)}₂(SnCH₂CH₂COO)(VW₁₀O₃₇)}₂]·31H₂O ((SnR)8-V3W35, R = CH₂CH₂COO) was assembled by a conventional synthetic method. (SnR)8-V3W35 is composed of one [VW₁₁O₃₉]^7- ({VW₁₁}) and two [VW₁₀O₃₇]^9- ({VW₁₀}) units connected by eight [Sn(CH₂)₂COO]²⁺ groups and a {W₄O₁₉} cluster. Interestingly, there exists a pentagonal bipyramid WO₇ polyhedral center surrounded by two SnCO₅ and three WO₆ octahedra, forming a pentagonal {(WO₇)W₃(SnR)₂} cluster in this polyoxometalate (POM), which is also the first example of a pentagonal structure formed by transition metals (TMs) and main group organometals in the POM family. Furthermore, the structure of this organic-inorganic hybrid POM also exhibits the largest number of organotin groups introduced into the POM system. It was characterized with various physico-chemical and spectroscopic methods, including X-ray single crystal and powder diffraction analysis, ¹¹⁹Sn and ⁵¹V NMR, IR, thermal gravimetric analysis (TGA), etc. In addition, the catalytic activity of (SnR)8-V3W35 as a mimic of peroxidase was evaluated using o-phenylenediamine (OPD) as a peroxidase substrate. The major factors influencing the oxidation reaction such as pH, the dosage of (SnR)8-V3W35, and concentrations of OPD and H₂O₂ were mainly studied. (SnR)8-V3W35 exhibits good peroxidase-like catalytic activity. From another perspective, the successful acquisition of (SnR)8-V3W35 further proves the instability and easy reassembly characteristics of TM-sandwich-type tungstovanadates, which also provides a new assembly strategy for synthesizing POM-estertin derivatives.