Syntheses and Structural Characterization of a Series of One-Dimensional Fluorotitanophosphates (NH₄)<i>_x</i>K₄_-<i>_x</i>[Ti₂PO₄F₉] (<i>x</i> = 0, 0.70, 1.00, 1.25)

A series of novel fluorotitanophosphates with a general formula (NH4)xK4 - x[Ti2PO4F9] (x = 0, 0.70, 1.00, 1.25, named as 1, 2, 3, and 4 respectively) have been synthesized under hydrothermal conditions. Their structures were determined by X-ray single-crystal diffraction technique, which show that all of the phases in this series contain an idental anionic fluorotitanophosphate chain, consisting of alternating linkage of PO4 tetrahedra and TiO2F4 octahedra. The fluorotitanophosphate chain is unique, which is different from the first titanophosphate chain found in [Ti3P6O27]·5[NH3CH2−CH2NH3]·2H3O. Another interesting observation of this series is that, by partial substitution of potassium by ammonium, the structure converts to a more-symmetric version, while maintaining all of the topological feature.