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)center dot 2H(2)O 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, H-1 and C-13 NMR), solubility product and conductance measurements. The complex salt crystallizes in the monoclinic space group P2(I)/n with a = 11.6865(3), b = 19.9546(4), c = 16.6808(3) angstrom, beta = 98.4730(10)degrees, V = 3847.5(6) angstrom(3), 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(delta+)center dot center dot center dot O-anion(delta-)] 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. (C) 2007 Elsevier B.V. All rights reserved.