Role of non-covalent interactions in binding of non-coordinating anions: Syntheses, characterization and single crystal structure determination of cobalt(III) complexes with 2,2′-biimidazole and 1,10-phenanthroline ligands

In an effort to understand the role of non-covalent interactions in binding of biologically and commercially important non-coordinating anions like I−, ClO 4 - and IO 4 - , four new mixed ligand Co(III) complex salts; [Co(phen)2Hbiim]Cl2·10H2O (1), [Co(phen)2Hbiim]I2·3H2O (2), [Co(phen)2Hbiim](ClO4)2 (3) and [Co(phen)2Hbiim] (IO4)2·0.5H2O (4) (where phen = 1,10-phenanthroline, Hbiim = 2,2′-biimidazole; monoanionic) have been synthesized. Elemental analyses, spectroscopic studies (IR, UV–Vis, 1H and 13C NMR), solubility product, conductance measurements were performed to characterize the complex salts. Single crystal X-ray structure determination revealed that complex salt 2 crystallizes in the triclinic crystal system ( P 1 ¯ ) while 3 and 4 crystallize in monoclinic crystal system with space group P21/c. In complex salts 3 and 4, the complex cations are arranged in the 2D sheets stabilized by N–H⋯N and C–H⋯π interactions. The anionic moieties are arranged like pillars in between these sheets which are stabilizing the three-dimensional architecture by C – H pen / Hbiim δ + ⋯ O anion δ - second sphere interactions besides electrostatic forces of attraction. The structural studies suggest that the non-covalent interactions like C–H⋯O, C–H⋯π, π–π stacking interactions cohesively play a decisive role in binding of biologically and commercially important anions (I−, ClO 4 - and IO 4 - ) by [Co(phen)2Hbiim]2+ in aqueous medium.