Second sphere coordination in anion binding: Synthesis, characterization of [Co(phen) 2CO 3]X· nH 2O where X = o-nitrophenolate(onp), p-nitrophenolate(pnp), 2,4-dinitrophenolate(dnp), 2,4,6-trinitrophenolate(tnp) and single crystal X-ray structures of [Co(phen) 2CO 3](onp)·2H 2O and [Co(phen) 2CO 3](dnp)·4.5H 2O

Abstract

In an effort to utilize [Co(phen) 2CO 3] + cation as a new host for mono-, di- and tri-substituted nitrophenolate anions, red coloured crystals of composition [Co(phen) 2CO 3](onp)·2H 2O, [Co(phen) 2CO 3](pnp), orange coloured precipitated product of [Co(phen) 2CO 3](dnp)·4.5H 2O (which gave red coloured crystals from acetone–water mixture) and orange-yellow coloured precipitated product of [Co(phen) 2CO 3](tnp) were obtained in good yields by reacting sodium salts of o-nitrophenol, p-nitrophenol 2,4-dinitrophenol and 2,4,6-trinitrophenol with [Co(phen) 2CO 3]Cl·5H 2O, respectively in 1:1 molar ratio in aqueous medium. These cobalt(III) complex salts have been characterized by elemental analyses, spectroscopic techniques (UV/Visible, IR and NMR) and conductance measurements. Single crystal X-ray structure determination of [Co(phen) 2CO 3](onp)·2H 2O and [Co(phen) 2CO 3](dnp)·4.5H 2O revealed the presence of discrete ions and lattice water molecules in the solid state. A strong network of hydrogen bond interactions through the weak second sphere coordination (C H…O (phenolate), C H…O (nitro), and strong interactions of type O H…O (water) besides the electrostatic interactions play a very important role in stabilizing the crystal lattice. The studies indicated that complex cation, [Co(phen) 2CO 3] + may preferentially bind nitrophenolate ions in the aqueous medium.