Two high-spin cobalt(III) complex anions with pyridinium-based cations: synthesis, structural elucidation and magnetic properties

Abstract

Two novel hybrid salts containing high spin tris(oxalato)cobaltate(III) complexes and pyridinium derivative isomer cations, viz. (C7H11N2)3[Co(C2O4)3]·nH2O (C7H11N2+ = 2-amino-4,6-dimethylpyridinium cation, n = 0 for salt 1; C7H11N2+ = 4-dimethylaminopyridinium, n = 4 for salt 2) were successfully isolated from aqueous solution. They were characterized using various physicochemical techniques, such as C, H, N microanalyses, thermogravimetric studies, FT-IR, UV-Vis, EDX, PXRD, single-crystal X-ray crystallography, and SQUID magnetometry. The size of the pyridinium derivative isomer cations has a major impact on the crystal structures. Salt 1 has a 3-D supramolecular framework formed by O–H···O hydrogen bonds between the high-spin [Co(C2O4)3]3− complex anion and the sterically encumbering 2-amino-4,6-dimethylpyridinium cations. The 3-D supramolecular framework of salt 2 is comprised of [Co(C2O4)3]3− complex anion, small size 4-dimethylaminopyridinium cations and uncoordinated water molecules via N–H···O and O–H···O hydrogen bonds. Structural cohesion is reinforced by π–π stacking interactions between the pyridine rings in both salts. Temperature-dependence magnetic moment (µ) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed robust antiferromagnetic ordering below TN = 25 K. The negative Weiss constant, θ = −55 K, confirmed the presence of antiferromagnetic interactions between Co(III) ions at low temperatures in 1 and the estimated effective magnetic moment of 4.5 μB supports the presence of the rare Oh high-spin Co(III) in this hybrid salt.