Second sphere coordination in binding of fluoroanions: Synthesis, spectroscopic characterization and single crystal X-ray structure determination of [Co(phen) 3](BF 4) 3·H 2O and [Co(phen) 3](PF 6) 3·CH 3COCH 3

Abstract

In an effort to capture fluoroanions by cationic cobalt(III) complex, two new cobalt(III) complex salts of composition [Co(phen) 3](BF 4) 3·H 2O ( 1) and [Co(phen) 3](PF 6) 3·CH 3COCH 3 ( 2) have been synthesized by the reaction of tris(1,10-phenanthroline)cobalt(III)chloride with sodium salts of tetrafluorborate and hexafluorophosphate (1:3 molar ratio) in aqueous medium. Single crystals of 1 were obtained directly from the reaction mixture when the solution was allowed to evaporate slowly at room temperature and single crystals of 2 were obtained by recrystallizing the precipitated product from acetone and water solution by slow evaporation. The newly synthesized complex salts were characterized by elemental analyses, TGA spectroscopic studies (IR, UV/Visible, 1H, 13C, 19F and 11B NMR), solubility product and conductance measurements. X-ray structure determination revealed ionic structures consisting of one [Co(phen) 3] 3+, three [BF 4] − ions and one lattice water molecule in complex salt 1, one [Co(phen) 3] 3+, three [PF 6] − anions and one acetone molecule as solvent of crystallization in complex salt 2. The three 1,10-phenanthroline ligands (each bidentate) coordinated to cobalt(III) showed distorted octahedral geometry around the central metal ion. Supramolecular hydrogen bonding networks between ionic groups [Co-phenCH δ+⋯ F anion δ - ] by second sphere coordination have been observed that stabilize crystal lattice besides electrostatic forces of attraction. The structural studies suggest that [Co(phen) 3] 3+ is a promising anion receptor for the fluoroanions (BF 4) − and (PF 6) −in aqueous medium.