Crystal structure, vibrational spectroscopy, and thermal behavior of K2Mg[B6O7(OH)6]2·4H2O

A crystal of the double metal borate K2Mg[B6O7(OH)6]2·4H2O was synthesized in K2B4O7·5H2O and MgCl2·6H2O solution at pH 7.5. Its crystal structure was determined from single crystal X-ray diffraction data. It belongs to the pī triclinic space group, with the following unit cell parameters: a = 7.495(6) Å, b = 7.795(6) Å, c = 10.877(9) Å, α = 108.067(11)°, β = 95.323(10)°, γ = 90.837(11)°, Z = 2, V = 600.9(8) Å3, Dc = 2.024 g/cm3. The crystal structure of K2Mg[B6O7(OH)6]2·4H2O consists of KO polyhedra, MgO octahedra and [B6O7(OH)6]2− polyborate anions. The assignments of the recorded FT-IR absorption frequencies and Raman shift of this compound were given. Dehydration of this compound occurs in two steps and leads to an amorphous phase which undergoes crystallization.