Expanding transition metal borate chemistry to include main group elements. High-pressure synthesis and structural relation of β-MgB${}_4$O${}_7$

The high-pressure/high-temperature synthesis of β-MgB${}_4$O${}_7$ at 9 GPa and 1200 °C is presented. The determination of its crystal structure by single-crystal X-ray diffraction has shown that the compound is isotypic to the transition metal borates with the structure type of β-MB${}_4$O${}_7$ (M = Mn-Zn). β-MgB${}_4$O${}_7$ crystallizes in the orthorhombic space group Cmcm with the lattice parameters a = 10.848(2), b = 6.513(2), and c = 5.144(1) Å. The structural relation between the normal-pressure phase α-MgB${}_4$O${}_7$ to the here presented high-pressure phase β-MgB${}_4$O${}_7$ and to other reference compounds is discussed.