Crystal structure and thermal behavior of Rb2Co[B6O7(OH)6]2·4H2O

Abstract A crystal of the complex borate Rb 2 Co[B 6 O 7 (OH) 6 ] 2 ·4H 2 O was synthesized in the molar ratio Rb 2 O/CoCl 2 /B 2 O 3 =4:1:9, and its structure was determined by single-crystal X-ray diffraction. It belongs to the P 1 triclinic space group, with the following unit cell parameters: a =7.549(1) A, b =7.872(1) A, c =10.980(2) A, α =107.87(1)°, β =94.83(1)°, γ =90.27(1)°, Z =2, V =618.45(19) A 3 . The crystal structure was solved from 2162 independent reflections until R =0.0127. The crystal structure of Rb 2 Co[B 6 O 7 (OH) 6 ] 2 ·4H 2 O consists of [B 6 O 7 (OH) 6 ] 2− polyborate anions, Co–O octahedra and Rb–O polyhedra. The isolated [B 6 O 7 (OH) 6 ] 2− polyborate anions are separated by free water molecules and Rb and Co cations. Dehydration of this hydrated mixed borate occurs in two steps and leads to an amorphous phase which undergoes crystallization.