Second sphere coordination in anion binding: Synthesis, Characterization and X-ray structure of tris(1,10-phenanthroline)cobalt(III) periodate dihydrate, [Co(phen)3](IO4)3·2H2O

Single crystals of [Co(phen)3](IO4)3·2H2O were obtained by dissolving the yellow coloured precipitated product (obtained by slowly mixing the separately dissolved tris(1,10-phenanthroline)cobalt(III) chloride with sodium periodate in aqueous medium in 1:3 molar ratio) in hot water and allowing it to evaporate slowly at room temperature. The newly synthesized complex salt was characterized by elemental analyses, spectroscopic studies (IR, UV/Visible, 1H and 13C NMR), solubility product and conductance measurements. The complex salt crystallizes in the monoclinic space group P21/n with a = 11.6865(3), b = 19.9546(4), c = 16.6808(3) Å, β = 98.4730(10)°, V = 3847.5(6) Å3, Z = 4. X-ray structure determination revealed an ionic structure consisting of one [Co(phen)3]3+, three [IO4]− ions and two lattice water molecules per asymmetric unit. The six nitrogen atoms, originating from three 1,10-phenanthroline ligands (each bidentate) show distorted octahedral geometry around the central Co(III) metal ion. Supramolecular hydrogen bonding networks between ionic groups [ Co - phenCH δ + … O δ - anion ] by second sphere coordination besides electrostatic forces of attraction have been observed that stabilize crystal lattice. The structural studies suggest that [Co(phen)3]3+ is a potential anion receptor for the periodate ion, (IO4)− in aqueous medium.