Terpyridine–Triarylborane Conjugates for the Dual Complexation of Zinc(II) Cation and Fluoride Anion

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• 作者：Young Hoon Lee ; Nguyen Van Nghia ; Min Jeong Go ; Junseong Lee ; Sang Uck Lee ; Min Hyung Lee
• 刊名：Organometallics
• 出版年：2014
• 出版时间：February 10, 2014
• 年：2014
• 卷：33
• 期：3
• 页码：753-762
• 全文大小：605K
• ISSN：1520-6041

文摘

A series of ditopic terpyridine鈥搕riarylborane conjugates (1鈥?b>3) in which 4鈥?ethynylterpyridine is linked to the para, meta, and ortho positions of the phenyl ring of dimesitylphenylborane (Mes₂PhB), respectively, were prepared to investigate the dual complexation behavior of the conjugates toward Zn(II) cation and fluoride anion. The crystal structures of the corresponding Zn(II) complexes (L路ZnCl₂, L = 1鈥?b>3) reveal the formation of a 1:1 adduct between ZnCl₂ and a conjugate, with a five-coordinate Zn(II) center bound to three nitrogen atoms and two chlorine atoms. In particular, the structure of ortho-substituted 3路ZnCl₂ in comparison with that of 3 indicates the presence of 蟺鈥撓€ interactions between the mesityl ring and ethynylene鈥損yridine fragment in 3路ZnCl₂. UV/vis absorption and fluorescence spectra of 1鈥?b>3 display low-energy bands mainly assignable to a 蟺(Ar) 鈫?p_蟺(B) (Ar = Mes and/or phenylene鈥揺thynylene) charge transfer (CT) transition. The transition in Zn(II) complexes has a 蟺(Mes) 鈫?蟺*(Ar) (Ar = terpyridine鈥揺thynylene) intramolecular CT nature with red shifts of both the absorption and emission bands in comparison to those of free conjugates. These spectroscopic features are further supported by TD-DFT calculations. UV/vis absorption and fluorescence titration experiments of 1鈥?b>3 toward Zn(II) and fluoride ion, respectively, show that while the absorption and fluorescence bands underwent gradual quenching upon addition of fluoride, the addition of ZnCl₂ gave rise to the red shifts of both bands. Fluoride titration experiments of Zn(II) complexes also resulted in gradual quenching of both the absorption and emission bands accompanied by the disappearance of emission color. Sequential addition of ZnCl₂ and fluoride to the conjugates reproduced the above binding behavior with an emission color change from deep blue to sky blue to dark.