Second sphere coordination in anion binding: Synthesis, spectroscopic characterization and single crystal X-ray structure determination of hexaamminecobalt(III) dichloride tetrafluoroborate

The reaction of hexaamminecobalt(III) chloride with sodium tetrafluoroborate in hot aqueous medium (1:1 molar ratio) leads to formation of hexaamminecobalt(III) dichloride tetrafluoroborate, [Co(NH3)6]Cl2·BF4. This cobalt(III) complex has been characterized by elemental analyses and spectroscopic techniques (e.g. UV–vis and IR). X-ray structure determination of this complex salt revealed the presence of discrete ions i.e., cation [Co(NH3)6]3+ and two different anions, two Cl− and one BF4− in the solid state. Crystal lattice is stabilized by electrostatic forces of attractions and hydrogen bonding interactions i.e. N–H⋯F− and N–H⋯Cl−. The formation of definite salt of composition with tetrafluoroborate ion suggest that [Co(NH3)6]3+ may be used as purely inorganic anion binding agent for weakly complexing fluoroanion, BF4−. This is the first X-ray structure determination of hexaamminecobalt(III) salt with tetrafluoroborate ion.