Stabilizing effects of large counter ion: Synthesis, characterization and single crystal X-ray structure determination of [Co(NH3)6][HgI4]I·H2O

In an attempt to synthesize [Co(NH3)6][Hg2I7], a new cobalt(III) complex salt, [Co(NH3)6][HgI4]I·H2O (1) was crystallized from a solution of hexaamminecobalt(III) bromide and potassium heptaiodatodimercurate(II) in aqueous medium in 1:1 M ratio. It has been characterized by elemental analyses, spectroscopic techniques (e.g. UV/visible, IR), solubility product and conductance measurements. The complex salt crystallizes in trigonal crystal system with space group R3c. Single crystal X-ray structure determination revealed the presence of discrete ions: [Co(NH3)6]3+ cation, one [HgI4]2−, one I− anions and one lattice water molecule. The crystal structure of complex salt, consist of a bilayered structure demonstrating “rosette structure” arrangements involving NH…I and NH…O hydrogen-bond interactions through second sphere coordination. The crystal lattice is stabilized by these non-covalent interactions besides electrostatic interaction.