Four Polyoxonibate-Based Inorganic–Organic Hybrids Assembly from Bicapped Heteropolyoxonibate with Effective Antitumor Activity

Four novel heteropolyoxonibate-based inorganic–organic hybrids {Cu­(en)₂}₆{GeNb₁₂V^IV₂O₄₂}·20H₂O (1), {Cu­(en)₂}₃K₂Na₄{GeNb₁₂V^IV₂O₄₂}·23H₂O (2), {Cu­(en)₂}₆{SiNb₁₂V^IV₂O₄₂}·18H₂O (3), and {Cu­(en)₂}₃K₂Na₄{SiNb₁₂V^IV₂O₄₂}·19H₂O (4) (en = ethanediamine), composed of polyoxoanions [TNb₁₂O₄₀]^16– (T = Si and Ge) and [Cu­(en)₂]²⁺ building blocks, were successfully synthesized under hydrothermal conditions by reaction of K₇HNb₆O₁₉·13H₂O, Cu­(Ac)₂·3H₂O, Na₂VO₃, Na₂SiO₃, or GeO₂ and en molecules. Polyoxoanion [TNb₁₂VIV₂O₄₂]^12– (T = Si and Ge) can be best described as a α-Keggin core [TNb₁₂O₄₀] with two [VO] units capping on its two “opened windows”. Compounds 1 and 3 are both composed of the bicapped heteropolyoxonibate core surrounded by a shell consisting of twelve [Cu­(en)₂]²⁺ groups, which represent a promising structural model toward core–shell nanostructures. Compounds 2 and 4 are also composed of a bicapped polyoxoanion [TNb₁₂V^IV₂O₄₂]^12– (T = Si, Ge) decorated by three metal–organic fragments [Cu­(en)₂]²⁺, forming a trisupporting polyoxoanion {[Cu­(en)₂]₃[TNb₁₂O₄₂V^IV₂]}^6–. Antitumor, electrochemical study, and UV–vis spectra indicate that compounds 1–4 exhibit effective antitumor activity against SGC7901 cells and HepG2 cells and could keep the structural integrity in this process.