Molecular recognition of pyramidal oxoanions using cationic cobaltammine: Synthesis, characterisation, X-ray structure determination and packing of [trans-Co(en)2Cl2]ClO3 and [trans-Co(en)2Cl2]BrO3

In an effort to explore [trans-Co(en)2Cl2]+ as anion binding agent for weakly coordinating and pyramidal in shape halate ions, green coloured single crystals of [trans-Co(en)2Cl2]ClO3 I and [trans-Co(en)2Cl2]BrO3 II have been obtained by slowly mixing the separately dissolved trans-dichlorobis(ethylenediamine)cobalt(III) chloride with appropriate metal halate salts in aqueous medium. The newly synthesised complex salts were characterised on the basis of elemental analysis and spectroscopic techniques (IR, UV/visible, 1H and 13C NMR). Single crystal X-ray structure determinations revealed their isomorphous nature. Both the compounds I and II crystallize in the triclinic space group P-1 with a=6.327 (1) Å, b=7.501(1) Å, c=13.788(1) Å, α=87.79 (1)°, β=80.56 (1)°, γ=71.38 (1)°, V=611.65(9) Å3, Z=2, R=0.0233 and a=6.338(1) Å, b=7.557(1) Å, c=14.089(1) Å, α=88.18(1)°, β=79.10(1)°, γ=70.83(1)°, V=625.56(14) Å3, Z=2, R=0.0269, respectively. Supramolecular hydrogen bonding networks between ionic groups: oxygen atoms of halates and NH groups of coordinated ethylenediamine molecules, i.e. N+–H⋯O− interactions involving second sphere coordination besides electrostatic forces of attraction have been observed. This suggests that [trans-Co(en)2Cl2]+ is a promising anion binding agent(receptor) for the weakly coordinating halate ions. The solubility product measurements indicate that the affinity of cationic cobaltammine [trans-Co(en)2Cl2]+ is greater for chlorate ion than bromate ion.