Synthesis, Crystal Structure and Vibrational Spectroscopy of NH4 [Co(NH3)5 (H2O)][B4O5 (OH)4]2·6H2O

A novel hydrated cobalt tetraborate complex NH4[Co(NH3)5(H2O)][B4O5(OH)4]2·6H2O, was synthesized by the reaction of NH4-borate aqueous with CoCl2 and its structure was determined by single crystal X-ray diffraction. The crystal system of this complex is orthorhombic, the space group is Pnma, and the unit cell parameters are a=1.2901(2) nm, b=1.6817(3) nm, c=1.1368(2) nm, α=β=γ=90°, V=2.4742(8) nm3, and Z=4. This compound contains infinite borate layers constructed from [B4O5(OH)4]2− units via hydrogen bonds. The adjacent polyborate anion layers are further linked together with the octahedral [Co(NH3)5(H2O)]3+ groups through hydrogen bonds to form 3D framework. The groups and guest water molecules are deposited in the empty space of this framework and interact with the layers by extensive hydrogen bonds. Infrared and Raman spectra (4000–400 cm−1) of NH4[Co(NH3)5(H2O)][B4O5(OH)4]2·6H2O were recorded at room temperature and analyzed. Fundamental vibrational modes were identified and band assignments were made. The middle band observed at 575 cm−1 in Raman spectrum is the pulse vibration of [B4O5(OH)4]2−.