Synthesis, structural characterization, and molecular modeling of dodecaniobate Keggin chain materials

Four new isostructural one-dimensional dodecaniobate Keggin materials, Na-12[Ti2O2][TNb1 2O40]-xH(2)O and Na-10[Nb2O2][TNb12O40]-xH(2)O with T = (Si or Ge), have been synthesized hydrothermally using a Lindqvist-ion salt, Na-7 [Nb6O19H]-15H(2)O, as the precursor. Their structure, consisting of chains of Keggin ions [TNb12O40](16-) linked by [Ti2O2](4+) or [Nb2O2](6+) bridges, was solved ab initio from powder diffraction data. The location of the charge-balancing sodium atoms and the water molecules was further investigated by molecular simulations. These compounds were also characterized by IR and solid-state H-1, Si-29, and Na-23 MAS NMR spectroscopies. The structural relationships between these and related phases based on similar Keggin ion building units are discussed.