Crystal structure and magnetic properties of trigonal prismatic Co(II) ions with a non-planar triptycene-based ligand Yoshiaki Shuku 1 , Rie Suizu 1 , Masahisa Tsuchiizu 2 , Kunio Awaga 1 1 Department of Chemistry & Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Japan 2 Department of Physics, Nara Women’s University, Japan Solid state physical properties such as conductivity and magnetic properties are discussed based on the crystal structures. Recently, highly symmetric crystal structures attracted attention due to their unique features, such as the exotic band structure (Drac cone) of honeycomb lattice, and spin frustration of triangle and Kagome lattice. In the previous work, we have prepared molecule-based highly symmetric 2D and 3D network structures by using non-planar 3-fold symmetric π-conjugated molecules such as triptycene derivatives. 1,2 In the present work we prepared a metal organic framework of a cobalt ion and a triptycene-based 3-fold symmetric bridging ligand with three o -benzoquinone moieties ( o -TT). The single crystal structure analysis revealed the 1:1 complex formation of Co ions and triptycene ligands [Co( o -TT)] and their 2D honeycomb network structure. In the structure, Co ions formed the trigonal prismatic coordination geometry. Six-coordinated complexes with octahedral coordination geometry are the most frequently observed for the Co ions and far fewer examples of the trigonal prismatic geometry have been reported due to their smaller ligand field stabilization energy. In the [Co( o -TT)] crystal, the formation of a honeycomb structure provides a steric effect to stabilize the local trigonal prismatic coordination geometry of the Co(II) ion. We carried out magnetic susceptibility measurements of [Co( o -TT)] and revealed the uniaxial anisotropy. Since the anisotropic axes of the trigonal prismatic ions were aligned in the same direction in the crystal structure, the magnetic measurements on [Co( o - TT)] clearly revealed a uniaxial magnetic anisotropy of the Co ion. The magnetic anisotropy on the trigonal prism coordination geometry was also analyzed using a theoretical model. References
1. Y. Shuku et al. Chem. Commun. 2018, 54 , 3815–3818. 2. A. Mizuno et al. J. Am. Chem. Soc. 2015, 137 , 7612–7615.
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