Cationic cobaltammines as anion receptors: Synthesis, characterization and X-ray structure of bis-(hexaamminecobalt(III)) tris-(hydrogenarsenate) tetrahydrate

The orange coloured single crystals of bis-(hexaamminecobalt(III)) tris-(hydrogenarsenate) tetrahydrate, [Co(NH3)6]2(HAsO4)3·4H2O, have been prepared by reacting aqueous solutions of hexaamminecobalt(III) chloride with disodium hydrogenarsenate in 1:1 molar ratio. The title complex salt was characterized by elemental analyses and spectroscopic studies (IR, UV/visible). X-ray crystal structure determination of the title complex salt revealed the presence of discrete ions, i.e., cation [Co(NH3)6]3+ and anion HAsO42− and four water molecules in the solid state. A strong network of hydrogen bond interactions (N–H⋯O (hydrogenarsenate), N–H⋯O (water), O–H⋯O (hydrogenarsenate)) stabilize the crystal lattice. The formation of definite salt and measurement of solubility products suggest that [Co(NH3)6]3+ may be used as an anion receptor for hydrogenarsenate anion.