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Ammonium citratoperoxotitanate(IV), (NH4)8[Ti4(C6H4O7)4(O2)4]·8H2O, was isolated in the solid form. Its crystal structure was solved and refined using single-crystal X-ray data. The compound crystallizes in a monoclinic cell with a = 10.237(2) Å, b = 17.537(4) Å, c = 14.713(3) Å, β = 100.35(1)° (Z = 2, fw = 1360.40, ρcalc = 1.74 g/cm3) and space group P21/n (No. 14). The determined structure of the titanium complex agrees well with the Raman and NMR spectroscopic data. We speculate that tight coordination of titanium in the complex molecule is responsible for the high stability of this compound against hydrolysis.

Raman spectra of Bi4-x La x Ti3O12 have been investigated. For an increasing degree of La doping, we find a substantial hardening of the vibration involving Bi atoms at the perovskite A site, whereas the Bi mode at the Bi2O2 layer is negligibly changed. From a comparison with a simple mass consideration, we identify a precise cation distribution, which indicates a pronounced site selectivity of La ions for the A site for x<∼ 1. At room temperature, the lowest mode at 28 cm-1 shows a significant softening with La doping. This behavior resembles the temperature dependence in the nondoped material (at constant composition). A remarkable correlation is found between the soft-mode frequency and T C for Bi4-x La x Ti3O12. We suggest that this correlation, as well as the soft-mode frequency for substituted materials, offers useful guidelines for designing materials in a controlled manner.

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