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{GeNb12VIV2O42}·20H2O (1), {Cu­(en)2}3K2Na4{GeNb12VIV2O42}·23H2O (2), {Cu­(en)2}6{SiNb12VIV2O42}·18H2O (3), and {Cu­(en)2}3K2Na4{SiNb12VIV2O42}·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 [TNb12VIV2O42]12– (T
= Si, Ge) decorated by three metal–organic fragments [Cu­(en)2]2+, forming a trisupporting polyoxoanion {[Cu­(en)2]3[TNb12O42VIV2]}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.