Intensive research on borophosphates has been carried throughout these years due to their rich structural chemistry and many potential applications. Becuse the B atoms reveal either triangular or tetrahedral coordination modes, the BO₃ and BO₄ as well as PO₄ groups are interconnected via common corners to form complex anionic structures, such as isolated species, oligomers, rings, chains, layers and frameworks. Therefore, the considerable variety in chemical structure of borophosphates provides a great deal objects for exploring novel compounds. In general, the P-O-P connections are extremely rare among borophosphates with the possible explanations found in Pauling’s fourth rule. However, novel borophosphate compounds are still discovered with time.

[B4P8O30] unit (left) and [B(P2O7)2] unit (right) give further examples of borophosphate　　　　  frameworks with a P-O-P connection

Prof. PAN Shilie and his Ph.D. students from Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences (XTIPC), have synthesized four new anhydrous mixed alkali-metal borophosphates, Li₂Cs₂B₂P₄O₁₅, LiK₂BP₂O₈, Li₃K₂BP₄O₁₄ and Li₃Rb₂BP₄O₁₄, through solid-state method. The four compounds are structurally related and constituted by anionic group layers and metallic polyhedra. The differences among them are mainly caused by the different fundamental building units (FBU). Li₂Cs₂B₂P₄O₁₅ contains a novel anionic partial structure [B₄P₈O₃₀], which provides further evidence that the P-O-P linkers exist in borophosphates. LiK₂BP₂O₈ contains very rare [BP₂O₈]_n^3n- layers with [B₂P₄O₁₆] as its FBU. Li₃K₂BP₄O₁₄ and Li₃Rb₂BP₄O₁₄ are isotypic, and they have [B(P₂O₇)₂] FBU with another kind of P - O - P linkers.