Synthesis, characterization and thermochemistry of K2B5O8(OH)·2H2O

A pure hydrated potassium borate K2B5O8(OH)·2H2O has been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, XRD, FT-IR, Raman spectra and DTA-TG. The crystal structure consists of two K–O polyhedra and [B5O8(OH)]2− polyborate anion. The enthalpy of formation was determined to be −4772.6 ± 4.0 kJ mol−1 by solution calorimetry.