12-Membered borophosphate rings in KNi₅[P₆B₆O₂₃(OH)₁₃]

The title compound, potassium pentanickel hexaborophosphate tridecahydroxide, was synthesized under hydrothermal conditions from the NiCl₂–K₃PO₄–B₂O₃–K₂CO₃–H₂O system. The crystal structure was determined using single-crystal X-ray diffraction at 100 K. The KNi₅[P₆B₆O₂₃(OH)₁₃] phase is cubic. For the three crystallographically distinct Ni centers, two occupy sites with 3 symmetry, while the third Ni and the K atom are located on sites. The structure is built from alternating borate and phosphate tetrahedra forming 12-membered puckered rings with K⁺ ions at the centers. These rings are arranged as in cubic dense sphere packing. A novel feature of the new crystal structure is the presence of linear trimers of face-sharing [NiO₆] octahedra occupying the octahedral interstices of this sphere packing, and of single [NiO₆] octahedra in the tetrahedral interstices. All oxygen corners of the Ni octahedra are linked to phosphate or borate tetrahedra of the 12-membered rings to form a mixed anionic framework.