Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged FeII Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine

Kazuyuki Takahashi; Mitsunobu Okai; Tomoyuki Mochida; Takahiro Sakurai; Hitoshi Ohta; Takashi Yamamoto; Yasuaki Einaga; Yoshihito Shiota; Kazunari Yoshizawa; Hisashi Konaka; Akito Sasaki

doi:10.1021/acs.inorgchem.7b02721

Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged Fe^II Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine

Inorg Chem. 2018 Feb 5;57(3):1277-1287. doi: 10.1021/acs.inorgchem.7b02721. Epub 2018 Jan 8.

Authors

Affiliations

¹ Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan.
² Research Facility Center for Science and Technology, Kobe University , 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan.
³ Molecular Photoscience Research Center, Kobe University , 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan.
⁴ Department of Chemistry, Faculty of Science and Technology, Keio University , 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
⁵ Institute for Materials Chemistry and Engineering, Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
⁶ XRD Application & Software Development, Rigaku Corporation , 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.

PMID: 29309129
DOI: 10.1021/acs.inorgchem.7b02721

Abstract

A series of [Fe^II(L)₂](BF₄)₂ compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2' upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2' demonstrated two-step and one-step abrupt SCO transitions, respectively. An X-ray single-crystal structural analysis revealed that one-dimensional and two-dimensional Fe cation networks linked by π stacking and sulfur-sulfur interactions were formed in 1 and 3, respectively. A thermodynamic analysis of the magnetic susceptibility for 1, 2', and 3 suggests that the enthalpy differences may govern SCO transition behaviors in the polymorphic compounds 2' and 3. A structural comparison between 1 and 3 indicates that the SCO behavior variations and crystal structure transformation in the present [Fe^II(L)₂](BF₄)₂ compounds can be interpreted by the relationship between the lattice enthalpies mainly arising from Coulomb interactions between the Fe cations and BF₄ anions as in typical ionic crystals.