From molecular to coordination complex: Two new supramolecular networks involving 4,4′-bipy, aminosalicylic acid and Co(II) ions

In this work, two new compounds, named (bpy)(Hbpy)⁺AS⁻·H₂O (1) and [Co(bpy)₂(H₂O)₄]ASCl·3H₂O (2) (where bpy is 4,4′-bipyridine, Hbpy is the protonated 4,4′-bipyridine and AS⁻ is the aminosalicylate anion), were obtained and investigated by single crystal X-ray diffraction and vibrational (Raman and infrared) spectroscopic techniques. For both complexes the existence of supramolecular interactions such as electrostatic, hydrogen bonding, π-stacking and CH⋯π was observed. All of them responsible for the crystalline lattice stability and the formation of a three-dimensional supramolecular arrangement. For compound (1) an interesting hydrogen bonding interaction was observed through the formation of cavities, and interacting with the Hbpy⁺ cation by π-stacking interaction. The vibrational spectra for both complexes are in a good agreement with the crystal data; for compound (1) the infrared spectrum exhibits bands at 1641 and 1195cm⁻¹, assigned to OCO and CO stretching modes of the aminosalicylate anion (carboxyl and hydroxyl groups, respectively). In the Raman spectra bands at 1598 and 1006cm⁻¹ refer to the νCC/νCN and νᵣᵢₙg modes, respectively, for Hbpy⁺ cation. For compound (2), it has been observed in the infrared spectrum bands at 1634 and 1193cm⁻¹ referring to the νOCO and νCO modes of aminosalicylate anion, whereas the bands in the Raman spectrum at 1617 and 1021cm⁻¹ are concerned to the νCC/νCN and νᵣᵢₙg modes of 4,4′-bipyridine. The successful synthesis and characterization of these two new compounds show that the mixed ligands can provide multiple interactions in a supramolecular structure, and the use of 4-aminosalicylic acid, which can act as both H-donor and H-acceptor, contributes with new features to the rapidly expanding area of supramolecular chemistry.