Three organic–inorganic polyoxoniobate-based compounds modified with Cu(ii) amine complexes: synthesis, characterization, and catalytic studies for oxidation of styrene†

Three novel organic–inorganic polyoxoniobate-based compounds modified with Cu(II) amine complexes were synthesized under hydrothermal conditions with the chemical formulas as follows: K_0.5[Cu(enMe)₂]₄[K_0.5SiNb₁₂O₄₀(VO)_4.25](OH)_1.5·9H₂O (1), K_0.5[Cu(enMe)₂]₄[K_0.5H₂PNb₁₂O₄₀(VO)₂]·12.5H₂O (2), and K_0.5[Cu(enMe)₂]₄[K_0.5H₂VNb₁₂O₄₀(VO)₂]·12.5H₂O (3) (enMe = 1,2-diaminopropane). These compounds were characterized by single crystal X-ray diffraction, infrared spectroscopy (IR), UV-Vis spectroscopy, elemental analysis and powder X-ray diffraction (PXRD) analysis. Notably, while these three compounds exhibit identical cell parameters, they possess distinct stoichiometric compositions and differing polyoxometalate building block structures. Typically, compounds with the same cell parameters are classified as isostructural, sharing identical structures with only minor elemental variations in their compositions. To the best of our knowledge, compounds 1–3 represent the first instances of compounds that share the same cell parameters yet are not isostructural. In this study, we not only synthesized these three compounds and thoroughly examined the differences in their structures and properties, but also investigated their catalytic performances as catalysts for the oxidation of styrene.