Second sphere coordination in anion binding: Synthesis, characterization of [Co(phen)2CO3]X·nH2O where X = o-nitrophenolate(onp), p-nitrophenolate(pnp), 2,4-dinitrophenolate(dnp), 2,4,6-trinitrophenolate(tnp) and single crystal X-ray structures

In an effort to utilize [Co(phen)2CO3]+ cation as a new host for mono-, di- and tri-substituted nitrophenolate anions, red coloured crystals of composition [Co(phen)2CO3](onp)·2H2O, [Co(phen)2CO3](pnp), orange coloured precipitated product of [Co(phen)2CO3](dnp)·4.5H2O (which gave red coloured crystals from acetone–water mixture) and orange-yellow coloured precipitated product of [Co(phen)2CO3](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)2CO3]Cl·5H2O, 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)2CO3](onp)·2H2O and [Co(phen)2CO3](dnp)·4.5H2O 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 (CH…O (phenolate), CH…O (nitro), and strong interactions of type OH…O (water) besides the electrostatic interactions play a very important role in stabilizing the crystal lattice. The studies indicated that complex cation, [Co(phen)2CO3]+ may preferentially bind nitrophenolate ions in the aqueous medium.