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Cooperative Spin-State Switching and Vapochromism of Mononuclear Ni(II) Complexes by Pyridine
Sotaro Kusumoto1, Kazumasa Inaba1, Harutoshi Suda1
1Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan.
Abstract:
Two mononuclear Ni(II) complexes (1 and 2) have been found to display color changes upon coordination/decoordination of pyridine, resulting in their structural transformation between square-planar and octahedral geometries as well as a change in their spin state. Compound 1 changes between red (1r) and yellow (1y) upon exposure to or elimination of pyridine, while 2 undergoes a two-step transformation, changing orange 2o (S = 0) ⇄ gray 2g' (S = 1) → yellow 2y' (S = 1) depending on the reaction time. The first step (2o → 2g') takes less than 45 min, which is significantly faster than the previously reported reaction time of 1 day for a Ni(II) complex/pyridine vapor system. Compound 2o reacting with pyridine can be easily prepared by dispersing 2g in methanol instead of annealing at high temperatures (130 °C), which can be applied to develop chemical sensors for pyridine utilizing color changes and/or magnetic switching.
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