Second-sphere coordination in anion binding: Synthesis and characterization of hexaamminecobalt(III) salts [Co(NH 3) 6](L) 3·3H 2O and [Co(NH 3) 6]Cl(L) 2, L=(CH 3) 3C 6H 2SO 3 and X-ray structure determination of [Co(NH 3) 6]Cl(L) 2

Abstract

The reaction of hexaamminecobalt(III) chloride with sodium salt of mesitylenesulphonic acid in aqueous medium (1:3 molar ratio) leads to formation of two products of hexaamminecobalt(III) salts [Co(NH 3) 6](L) 3·3H 2O and [Co(NH 3) 6]Cl(L) 2, L=(CH 3) 3C 6H 2SO 3. These cobalt(III) complexes have been characterized by elemental analyses and spectroscopic techniques (e.g. UV/Visible, IR and NMR). Single crystal X-ray structure determination of title complex salt revealed supramolecular hydrogen bonding network between ionic groups (i.e. oxygen atoms of C 9H 11SO 3 − and Cl −) and NH groups of coordinated NH 3 molecules, i.e. N–H⋯O − and N–H⋯Cl − interactions resulting in bilayer formation, the bilayers being anchored by Cl − ions. The formation of definite salts of composition [Co(NH 3) 6](L) 3·3H 2O and [Co(NH 3) 6]Cl(L) 2 and measurement of solubility products suggests that [Co(NH 3) 6] 3+ present in [Co(NH 3) 6]Cl 3 is a promising purely inorganic anion binding agent for the weakly coordinating sulphonate anion.