The Structural and Magnetic Properties of Fe^II and Co^II Complexes with 2-(furan-2-yl)-5-pyridin-2-yl-1,3,4-oxadiazole

Two novel coordination compounds containing heterocyclic bidentate <i>N</i>,<i>N</i>-donor ligand 2-(furan-2-yl)-5-(pyridin-2-yl)-1,3,4-oxadiazole (fpo) were synthesized. A general formula for compounds originating from perchlorates of iron, cobalt, and fpo can be written as: [M(fpo)₂(H₂O)₂](ClO₄)₂ (M = Fe(II) for (<b>1</b>) Co(II) for (<b>2</b>)). The characterization of compounds was performed by general physico-chemical methods&#8212;elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) in case of organics, and single crystal X-ray diffraction (sXRD). Moreover, magneto-chemical properties were studied employing measurements in static field (DC) for <b>1</b> and X-band EPR (Electron paramagnetic resonance), direct current (DC), and alternating current (AC) magnetic measurements in case of <b>2</b>. The analysis of DC magnetic properties revealed a high spin arrangement in <b>1</b>, significant rhombicity for both complexes, and large magnetic anisotropy in <b>2</b> (<i>D</i> = &#8722;21.2 cm^&#8722;1). Moreover, <b>2</b> showed field-induced slow relaxation of the magnetization (<i>U</i>_eff = 65.3 K). EPR spectroscopy and ab initio calculations (CASSCF/NEVPT2) confirmed the presence of easy axis anisotropy and the importance of the second coordination sphere.

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