Structural insights into three phosphates with distinct polyanionic configurations

Abstract

Three mixed-metal phosphates, namely, centrosymmetric LiSrP₃O₉ and LiCsP₂O₆ as well as noncentrosymmetric K₂SrP₄O₁₂ have been synthesized by the high temperature solution method. These structures were characterized by single-crystal X-ray diffraction and their P–O units are shown to feature distinct polyanionic configurations from [PO₃]_∞ chains in LiSrP₃O₉ to [P₄O₁₂]⁴⁻ rings in LiCsP₂O₆ and K₂SrP₄O₁₂. Besides, K₂SrP₄O₁₂ shows a moderate second harmonic generation response about 0.6 times that of KH₂PO₄ and can be applied as a potential nonlinear optical material for the ultraviolet spectral region. Thermal behaviour analyses indicate that the compounds LiSrP₃O₉ and K₂SrP₄O₁₂ remain stable up to 659 and 698 °C, respectively. In addition, the crystal structures, thermal stabilities and infrared spectra of the title compounds have been examined.