Synthesis, crystallization and Hirshfeld surface analysis of transition metal carboxylate pentapyridines

Abstract

A new compound 2,6-bis(1,1-di(pyridin-2-yl)ethyl)isonicotinic acid (Py5Me₂COOH) was successfully synthesised and metalated with nickel, cobalt and copper to give the corresponding complexes [Co(Py5Me₂COO⁻)(OH⁻)]¹⁺ (1), [Ni(Py5Me₂COO⁻)(H₂O)]¹⁺ (2) and [Cu₄(Py5Me₂COO⁻)₂(H₂O)₄(OH⁻)₂]⁴⁺ (3). The complexes were characterized through HD-MS, FT-IR and UV-vis spectroscopic methods. Crystals suitable for single X-ray diffraction were successfully grown and reveals complex 1 and 2 maintain the conventional distorted octahedral configuration. Complex 3 resulted in the formation of a square pyramidal tetra-copper di-ligand structure. Hirshfeld surfaces mapped with d_norm and shape index functions were used to give further information on interaction types within the crystal. Analysis of the 2D fingerprint plots shows the dominant interactions within the crystal packing to be H⋯H and O⋯H contacts, with complex 1 forming a three-dimensional hydrogen bonded polymer. Crystal packing in complex 3 is strongly influenced by fluorine interactions; (H⋯F) and the packing structure of complex 2 is shaped by π based interactions. The orientation of these contacts reveals the structure directing effects of the carboxylate, with the weaker aromatic interactions arranging to give priority to the stronger and more directional hydrogen bonds.