Second sphere coordination in anion binding: Synthesis and spectroscopic characterisation of [trans-Co(en)2Cl2]X (X=SCN or N3). Single crystal X-ray structure determination and packing of [trans-Co(en)2Cl2]N3

In an effort to explore [trans-Co(en)2Cl2]+ as anion receptor for linear thiocyanate and azide ions, green coloured microcrystalline [trans-Co(en)2Cl2]SCN I and single crystals of [trans-Co(en)2Cl2]N3 II have been obtained by slowly mixing the separately dissolved trans-dichlorobis(ethylenediamine)cobalt(III) chloride with ammonium thiocyanate and sodium azide respectively in aqueous medium in 1:1 molar ratio. The newly synthesised complex salts were characterised on the basis of elemental analysis and spectroscopic techniques (IR, UV/vis, 1H and 13C NMR). Single crystal X-ray structure determination of II revealed that it crystallizes in the triclinic space group P 1 with a=6.293(1) Å, b=6.696(1) Å, c=7.116(1) Å, α=94.02(1)°, β=111.42(1)°, γ=99.86(1)°, V=272.13(7) Å3, Z=1, R=0.0183. Supramolecular hydrogen bonding networks between ionic groups: nitrogen atoms of azide group and NH groups of coordinated ethylenediamine molecules, i.e. N–H⋯N− interactions by second sphere coordination besides electrostatic forces of attraction have been observed which probably exist in case of thiocyanate also. This suggests that [trans-Co(en)2Cl2]+ is a promising anion receptor for the linear ions SCN− and N3−. The solubility product measurements indicate that the affinity of cationic cobaltammine [trans-Co(en)2Cl2]+ is greater for azide ion than thiocyanate ion.