La3B6O13(OH): The First Acentric High‐Pressure Borate Displaying Edge‐Sharing BO4 Tetrahedra.

La3B6O13(OH) was obtained by a high‐pressure/high‐temperature experiment at 6 GPa and 1673 K. The compound crystallizes in the space group P21 (no. 4) with the lattice parameters a=4.785(2), b=12.880(4), c=7.433(3) Å, and β=90.36(10)°, and is built up of corner‐ as well as edge‐sharing BO4 tetrahedra. It represents the first acentric high‐pressure borate containing these B2O6 entities. The compound develops borate layers of „sechser"‐rings with the La3+ cations positioned between the layers. Single‐crystal and powder X‐ray diffraction, vibrational and MAS NMR spectroscopy, second‐harmonic generation (SHG) and thermoanalytical measurements, as well as computational methods were used to affirm the proposed structure and the B2O6 entities. [ABSTRACT FROM AUTHOR]