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

La 3 B 6 O 13 (OH) was obtained via a high-pressure/high-temperature experiment at 6 GPa and 1673 K. The compound crystallizes in the space group P 2 1 (no. 4) with the lattice parameters a = 4.785(2), b = 12.880(4), c = 7.433(3) A, and beta = 90.36(10) degrees , and is built up of corner- as well as edge-sharing BO 4 tetrahedra. It represents the first acentric high-pressure borate containing these B 2 O 6 entities. The compound develops borate layers of "sechser"-rings with the La 3+ cations positioned within the layers. Single-crystal and powder X-ray diffraction, vibrational and MAS NMR spectroscopy, SHG and thermoanalytical measurements as well as computational methods were used to affirm the proposed structure and the B 2 O 6 entities.