Second sphere coordination in anion binding: Synthesis, characterization and X-ray structure of [ cis-diazidobis(ethylenediamine)cobalt(III)][ trans-diamminetetranitrocobaltate(III)

Abstract

Dark maroon coloured single crystals of [ cis-Co(en) 2(N 3) 2][ trans-Co(NH 3) 2(NO 2) 4] were obtained by slowly mixing the separately dissolved [ cis-diazidobis(ethylenediamine)cobalt(III)] nitrate with potassium [ trans-diamminetetranitrocobaltate(III)] in aqueous medium in 1:1 molar ratio. The complex salt was characterized by elemental analyses, spectroscopic studies (IR, UV/visible, 1H and 13C NMR) and solubility product measurements. The title complex salt crystallises in triclinic space group P 1 ¯ having cell dimensions, a = 7.4210(2), b = 11.0618(3), c = 12.3763(3) Å, α = 95.5850(10), β = 91.4400(10), γ = 108.9070(10)°, V = 954.853 Å 3, Z = 2 and R-factor = 5.16%. Single crystal X-ray structure determination revealed an ionic structure consisting of [ cis-Co(en) 2(N 3) 2] + and [ trans-Co(NH 3) 2(NO 2) 4] −. Supramolecular hydrogen bonding networks involving second sphere coordination like [ NH en + ⋯ X anion - ] besides electrostatic forces of attraction have been observed to stabilize the crystal lattice. This is the first crystal structure of a salt containing [ trans-diamminetetranitrocobaltate(III)] anion and [ cis-diazidobis(ethylenediamine)cobalt(III)] cation. The formation of complex salt of definite composition and solubility product measurements show that the cationic cobaltammine [ cis-Co(en) 2(N 3) 2] + is a potential anion receptor for complex anion [ trans-Co(NH 3) 2(NO 2) 4] − in aqueous medium.