Cationic cobaltammines as anion receptors: a convenient synthesis and the X-ray structure of hexaamminecobalt(III) chloride dichromate monohydrate

Abstract

Orange-colored single crystals of hexaamminecobalt(III) chloride dichromate monohydrate, [Co(NH3)6]ClCr2O7·H2O, were prepared by reacting hot aqueous solutions of hexaamminecobalt(III) chloride and potassium dichromate in a 1:1 molar ratio and allowing the mixture to cool slowly to room temperature. The salt was characterized by elemental analyses and spectroscopic studies. A single-crystal X-ray structure determination revealed that the salt crystallizes in space group P21/c with a = 10.0218(9), b = 9.3216(8), c = 16.2203(13) Å, β = 112.962(6)°, V = 1395.2(2) Å3, Z = 4 and R = 0.0326. In the salt, a strong network of hydrogen bonds (predominantly N–H···O, N–H···Cl–) between the hexaamminecobalt(III) cation, the water molecule, the chloride ion and oxygen atoms of the dichromate ion represents the second sphere coordination and suggests that [Co(NH3)6]3+ may be used as an anion receptor for the dichromate ion.