Synthesis, crystal structure, magnetic properties and Hirshfeld surface analysis of two cobalt(II) complex anions templated by pyridinium-based cations

Abstract

Two organic–inorganic hybrid salts, (C6H9N2)2[Co(C2O4)2]·H2O (1) and (C5H7N2)2[Co(C2O4)2(H2O)2] (2) (C6H9N2+ = 2-amino-3-methylpyridinium; C5H7N2+ = 4-aminopyridinium) have been obtained. Salt 1 is characterized by the formation of one-dimensional chains of the anionic complexes [Co(C2O4)2]2-, with the Co(II) centers located in a distorted (2 + 2 + 2) octahedral environment of six oxygen atoms from three chelating oxalato(2 − ) ligands. By contrast, salt 2 features discrete anionic complexes [Co(C2O4)2(H2O)2]2- with distorted (4 + 2) octahedral CoO6 coordination sphere formed by two bidentate O,O-donor oxalato(2 − ) ligands in the equatorial plane and two aqua ligands in the axial positions. Hydrogen bonding interactions of the type OH∙∙∙O and NH∙∙∙O along with π–π stacking interactions between pyridine rings contribute to the stabilization of the 3-D supramolecular frameworks in 1 and 2. Temperature-dependence magnetic moment (µ) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed strong antiferromagnetic ordering below TN = 25 K for 1, a behavior which is confirmed by the negative Weiss constant, θ = − 27.6 K. By contrast, in 2, the Weiss constant, θ = 0 K is in line with a paramagnetic behavior. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint plots (2D-FP) revealed that in 2, the structure is dominated by H∙∙∙O/ H∙∙∙O and H∙∙∙H contacts.