Second-sphere coordination in anion binding: Synthesis and characterization of hexaamminecobalt(III) salts [Co(NH3)6](L)3·3H2O and [Co(NH3)6]Cl(L)2, L=(CH3)3C6H2SO3 and X-ray structure determination of [Co(NH3)6]Cl(L)2

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(NH3)6](L)3·3H2O and [Co(NH3)6]Cl(L)2, L=(CH3)3C6H2SO3. 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 C9H11SO3− and Cl−) and NH groups of coordinated NH3 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(NH3)6](L)3·3H2O and [Co(NH3)6]Cl(L)2 and measurement of solubility products suggests that [Co(NH3)6]3+ present in [Co(NH3)6]Cl3 is a promising purely inorganic anion binding agent for the weakly coordinating sulphonate anion.