The New High-Pressure Sodium Tetraborate HP-Na2B4O7

The new polymorph of sodium tetraborate HP-Na2B4O7 was synthesized under high-pressure / high-temperature conditions of 6 GPa and 1000 °C in a multianvil apparatus with a Walker-type module. HP-Na2B4O7 crystallizes with nine formula units per cell in the trigonal chiral space groups P3221 or P3121. The parameters are a = 765.5(2), c = 2142.3(4) pm, V = 1.0872(3) nm3, R1 = 0.0581, and wR2 = 0.0809 (all data). The crystal structure of HP-Na2B4O7 is built up from interconnected “sechser” rings of alternating corner-sharing BO3 and BO4 groups.