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(mu-mell)(H2O)(2)].10H(2)O}(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 degrees 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.