A₃Sr₂P₇O₂₁ (A = Rb, Cs): Two Polyphosphates Based on Different Types of P-O Chains and Ring Structures

Area of Science:

• Inorganic Chemistry
• Solid-State Chemistry
• Crystallography

Background:

• Polyphosphates exhibit diverse polymerization of phosphate groups, influencing material properties.
• Alkali metal cations play a crucial role in dictating the structural arrangements of inorganic compounds.

Purpose of the Study:

• To synthesize and characterize novel rubidium and cesium strontium polyphosphates.
• To investigate the impact of alkali metal cations on phosphate polymerization and crystal structures.
• To explore the optical properties and structure-property relationships of the synthesized compounds.

Main Methods:

• Spontaneous nucleation method for crystal growth.
• Single-crystal X-ray diffraction for structural determination.
• Infrared (IR) spectroscopy and UV-vis-NIR diffuse reflectance spectroscopy for optical properties.
• First-principles theoretical calculations for structure-property analysis.

Main Results:

• Synthesis and structural elucidation of Rb3Sr2P7O21 and Cs3Sr2P7O21.
• Rb3Sr2P7O21 exhibits a rare coexistence of two distinct [PO3]∞ linear chains.
• Cs3Sr2P7O21 displays an unusual combination of isolated [P4O12] rings and 1D [PO3]∞ chains.
• Alkali metal cations (Rb+ and Cs+) influence polymerization and lead to different space groups.

Conclusions:

• The study reveals novel polyphosphate structures with unique polymerization modes.
• Alkali metal cations are key in directing the structural diversity and space group of these phosphates.
• The synthesized compounds possess interesting optical properties influenced by their distinct structural features.