First X-ray structure of discrete anion [HgBr5]3−: Synthesis, characterization and single crystal X-ray structure determination of [Co(NH3)6][HgBr5]

A new cobalt(III) complex salt, [Co(NH3)6][HgBr5](1) was crystallized from a solution of hexaamminecobalt(III)bromide and potassium tetrabromomercurate(II) in aqueous medium in 1:1 molar ratio. This complex salt has been characterized by elemental analyses, spectroscopic techniques (e.g. UV/Visible, IR), solubility product and conductance measurements. The complex salt crystallizes in Orthorhombic crystal system with space group Pnma. Single crystal X-ray structure determination revealed the presence of discrete ions: [Co(NH3)6]3+ cation and a new anion [HgBr5]3−. This is the first structural report of a complex salt containing this new anion. The structure consists of stacks of cations and anions demonstrating supramolecular arrangements through N–H⋯Br hydrogen-bond interactions. The crystal lattice is stabilized by these non-covalent interactions besides electrostatic interaction.