Binding of inorganic oxo-anions to cationic cobaltammine: Synthesis, characterization, X-ray structures determination and DFT calculations of [Co(NH 3) 6]Cl 2(ClO 3), [Co(NH 3) 6]Br 2(ClO 3) and [Co(NH 3) 6]Cl 2(IO 3) · H 2O

Abstract

Single crystals of [Co(NH 3) 6]Cl 2(ClO 3) ( 1), [Co(NH 3) 6]Br 2(ClO 3) ( 2) and [Co(NH 3) 6]Cl 2 (IO 3) · H 2O ( 3) suitable for X-ray structure determinations were obtained directly by reacting hexaamminecobalt(III) halide with appropriate metal halates in 1:1 molar ratio in hot aqueous medium. These hexaamminecobalt(III) complexes have been characterized by spectroscopic studies (e.g. UV/Visible and IR). Single crystal X-ray structure determination of title complex salts revealed the presence of discrete ions, i.e., cation [Co(NH 3) 6] 3+ and mixed anions Cl − and ClO 3 - or Br − and ClO 3 - or Cl − and IO 3 - in the solid state. Crystal lattice is stabilized by electrostatic forces of attraction and hydrogen bonding interactions (N–H⋯O −, N–H⋯Cl − or N–H⋯Br −). The formation of definite salts of composition with halate ions suggests that [Co(NH 3) 6] 3+ may be used as purely inorganic anion binding agent for these weakly coordinating oxo-anions. The DFT calculations have been carried out to calculate molecular volumes of the oxoanions and separation between two successive cation layers.