Role of second-sphere coordination in anion binding: Synthesis, characterisation and X-ray structure of hexaamminecobalt(III) chlorise hydrogen phthalate trihydrate and sodium hexamminecobalt(III) benzoate monohydrate

In an effort to utilize [Co(NH3)(6)](3+) cation as a new host for carboxylate ions, orange coloured crystalline solids of composition [Co(NH3)(6)]Cl(C8H5O4)(2)(.)3H(2)O (1) and Na[Co(NH3)(6)](C7H5O2)(4)(H2O)-H-. (2) were obtained by reacting hot aqueous solutions of hexaamminecobalt(III) chloride with potassium hydrogen phthalate and sodium benzoate in 1:3 molar ratio, respectively. The title complex salts were characterized by elemental analyses and spectroscopic studies (IR, UV/Visible and NMR). Single crystal X-ray structure determinations revealed the formation of second-sphere coordination complexes based on hydrogen bond interactions. In complex salt 1 only two out of three ionisable chloride ions present in [Co(NH3)(6)]Cl-3 were replaced by two C8H5O4- ions whereas in complex salt 2 all the three ionisable chloride ions present in [Co(NH3)6]Cl-3 were replaced and the final product was an adduct with another mole of sodium benzoate in solid state. The crystal lattice is stabilized by electrostatic forces of attraction and predominantly N-(HO)-O-... interactions. (c) 2005 Elsevier B.V. All rights reserved.