Capture of aromatic carboxylate anion through second sphere coordination: Topological complementarity of [cis-Co(en)2(N3)2]+ and C7H3ClNO4- ions

[cis-Co(en)2(N3)2]C7H3ClNO4·1.25H2O (Cocnb) was synthesised and detailed packing analyses were undertaken to delineate the topological complementarity of [cis-Co(en)2(N3)2]+ and a 2-chloro-4-nitro benzoate anion (cnb) for second sphere coordination in the crystal lattice. The complex was completely characterised by elemental analyses, spectroscopic studies (IR, UV/visible, 1H and 13C NMR). The compound crystallizes in the monoclinic (space group C2/c) with a = 21.9843(18), b = 8.7959(7), c = 23.0121(18) Å, β = 116.426(1)°, V = 3984.9(6) Å3, and Z = 8. In the crystal lattice, discrete ions of [cis-Co(en)2(N3)2]+ and cnb are arranged in ⋯A–B–A–B⋯ pattern (in both a and c directions of the lattice) forming columns of anions and cations. The anionic columns are π stacked and are involved in extensive hydrogen bonding interaction. It appears that the topological feature of [cis-Co(en)2(N3)2]+ is conducive for generating second sphere interactions with aromatic carboxylates. This strategy may be used as a viable method for the capture of aromatic carboxylate anions.