Crystallographic, spectroscopic, thermal and computational studies of polymeric cobalt(II)–mellitate complex with 2,2′-bipyridine

Abstract

Orange single crystals of new polymeric cobalt(II) complex {[Co(bipy)(H2O)4]2[Co(μ-mell)(H2O)2]·10H2O}n, 1, were synthesized by slow evaporation method at room temperature (bipy = 2,2′-bipyridine, mell = hexaanion of mellitic acid) and its crystal structure was determined by single-crystal X-ray diffraction. The complex 1 was characterized based on elemental analysis, FTIR spectroscopy and thermal (TG/DTA) analysis followed by computational analysis of noncovalent interactions and quantum chemical calculations of interaction energies. In 1, two crystallographically different Co(II) atoms adopt a deformed octahedral geometry, while bridging mell acts as a tetrakis monodentate ligand allowing the development of wavy-like anionic chains running along [100] direction. The 3D supramolecular network of 1 is composed of alternating supramolecular and water layers connected by hydrogen bonds. The supramolecular layer is formed of ionic interactions between complex cations and polymeric complex anions, established mainly through O–H···O hydrogen bonds, as well as stacking interactions between bipy ligands, while the water layers are comprised of hydrogen bonded lattice water molecules. Upon heating up to 1200 °C in nitrogen and air atmosphere, complex 1 showed multiple-step degradation that resulted in the formation of Co and Co3O4, respectively. Computed Hirshfeld surfaces and 2D fingerprint plots indicated that O–H···O hydrogen bonds are the most dominant in the crystal structure, while the shape index and curvedness mapped on the Hirshfeld surfaces of 1 revealed that stacking interactions have an important role in the stabilization of the crystal packing. Quantum chemical calculations showed that, aside from ionic hydrogen-bonded interaction between cation and anionic polymer, the important role in the stability of supramolecular structure of 1 is played by hydrogen bonds of cation and anionic polymer with lattice water, as well as by stacking interactions between bipy ligands.