Structure, optical and magnetic properties of the pyridinium cobaltate (C6H9N2)2[CoCl4

Abstract

The reaction of 2-amino-4-methylpyridine (L) with CoCl2·6H2O in hydrochloric acid gave the chlorocobaltate (HL)2[CoCl4] in 82% yield. X-ray diffraction of the blue crystalline material showed isolated [CoCl4]2– tetrahedra in the structure, connected to the aromatic 2-amino-4-methyl pyridinium cations through H bonding while the cations show π-stacking. FT-IR spectroscopy in conjunction with Hirshfeld surface analysis confirmed the importance of the 2-amino function in the cations for the hydrogen bonding. The material is thermally stable up to 270 °C. Intense UV–vis absorptions in the range 200–400 nm were assigned to π–π* transitions in the pyridinium cation, weaker features in the range 600–750 nm were due to ligand-field transitions in the d7 high-spin system [CoCl4]2–. Excitation at 370 nm led to an intense blue-green emission at λem = 473 nm attributable to excited π–π* states. The molar susceptibility measured over a range of 5–300 K reveals paramagnetic behavior at high temperature range with an effective magnetic moment of µeff = 4.74 µB indicating a significant spin–orbit coupling contribution adding to the spin-only value of 3.87 µB expected for Co(II) with 3d7 high spin configuration.