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

Abstract

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.