Synthesis, Characterization, and Magnetic Properties of Iron(II) Complex with 2,6-Bis(pyrazol-3-yl)pyridine Ligand and Tetracyanonickelate Anion

Fitriani Fitriani (Inorganic and Physical Chemistry Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia)
Irma Mulyani (Inorganic and Physical Chemistry Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia)
Djulia Onggo (Inorganic and Physical Chemistry Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia)
Kristian Handoyo Sugiyarto (Department of Chemistry Education, Universitas Negeri Yogyakarta, Jl. Colombo No. 1, Yogyakarta 55281, Indonesia)
Ashis Bhattacharjee (Department of Physics, Visva-Bharati University, Santiniketan 731204, India)
Hiroki Akutsu (Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan)
Anas Santria (Research Center for Chemistry, National Research and Innovation Agency, Kawasan PUSPITEK, Serpong, Tangerang Selatan, Banten 15314, Indonesia)

Indonesian Journal of Chemistry
Vol 23, No 4 (2023)

The complex containing iron(II), 2,6-bis(pyrazol-3-yl)pyridine (3-bpp) as ligand, and tetracyanonickelate as counter anion has been synthesized and characterized. The characterization data suggest the corresponding formula of [Fe(3-bpp)2][Ni(CN)4]·4H2O. Meanwhile, the SEM–EDX analysis image confirms the existence of all elements contained in the complex except the hydrogen atom. The infrared spectra exhibit vibration bands of the functional groups of 3-bpp ligand and [Ni(CN)4]−1 anion. From magnetic property measurement, the complex's molar magnetic susceptibility (XMT) value is 2.65 emu mol−1 K at 300 K, which contains about 75% high-spin state of the Fe(II) complex. Upon lowering the temperature, the XMT value gradually decreases around 1.37 emu mol−1 K at 13 K. It decreases sharply to about 0.73 emu mol−1 K at 2 K. These values reveal that Fe(II) complex is in the low-spin (LS) state. As a result, the complex exhibited spin-crossover characteristics of gradual transition without thermal hysteresis, and the transition temperature occurred below room temperature with a transition temperature (T1/2) close to 140 K. The spin crossover property of the complex is supported by a thermochromic reversible color change from red-brown at room temperature to dark brown on cooling in liquid nitrogen associated with the high-spin to low-spin transition.