Additions and corrections

Reversible modulation of -association between 3,6-disubstituted carbazole ligands in a multistep assembling process

Norie Inukai, Junpei Yuasa and Tsuyoshi Kawai

Chem. Commun., 2010, 3929–3931 (DOI: 10.1039/c001287d) Amendment published 27 July 2012

Background

We have previously reported that carbazole ligand (Im₂Cz) formed a dimer complex having multiple pi-stacking interactions in Chem. Commun (DOI: 10.1039/c001287d). During the course of our work, we performed NMR titration of Im₂Cz by zinc ion (Zn²⁺) to investigate complex formation between Im₂Cz and Zn²⁺. The NMR titration analysis revealed that the doublet peak due to aromatic proton of the carbazole ring is upfield shifted considerably from 7.75 to 5.73 ppm (Fig. 2a) in the presence of Zn²⁺, suggesting formation of pi-stacking interactions between carbazole ligands during complexation with Zn²⁺. The NMR titration analysis also suggested two sets of carbazole rings and four sets of imidazole rings of the Zn²⁺ complex located in different chemical environments. According to the detailed NMR analysis, we initially assumed two types of dimer complex, [(Im₂Cz)₄-Zn²⁺]₂ and [(Im₂Cz)₂-Zn²⁺]₂, were possible structures for the Zn²⁺ complex that have pi-stacking interactions. In order to determine the stoichiometry of the Zn²⁺ complex, we performed UV-Vis. titration of Im₂Cz by Zn²⁺, where the absorbance change at lambda = 365 nm is plotted against [Zn²⁺]/[Im₂Cz]₀ (Fig. 1). The titration analysis suggests the stoichiometry of four Im₂Cz ligands per Zn²⁺ at [Zn²⁺]/[Im₂Cz]₀ = 0.25 and three Im₂Cz ligands per Zn²⁺ at [Zn²⁺]/[Im₂Cz]₀ = 0.33. This result suggests formation of [(Im₂Cz)₄-Zn²⁺]₂, which converts to (Im₂Cz)₃-Zn²⁺ at [Zn²⁺]/[Im₂Cz]₀ = 0.33. Thus, we have finally concluded [(Im₂Cz)₄-Zn²⁺]₂ to be the most likely substance of the dimer complex.

Correction and Additional Information

We recently become aware of the past evaluation of the concentration of Im₂Cz (=[Im₂Cz]₀) being erroneous. Then, we re-performed the titration twice and observed good reproducibility with the corrected concentration. The corrected results of the UV-vis titration are provided in Fig. C1. This corrected-result suggests the stoichiometry of two Im₂Cz ligands per Zn²⁺ at [Zn²⁺]/[Im₂Cz]₀ = 0.50 and three Im₂Cz ligands per two Zn²⁺ ions at [Zn²⁺]/[Im₂Cz]₀ = 0.66, being consistent with formation of [(Im₂Cz)₂-Zn²⁺]₂ and [(Im₂Cz)₃-(Zn²⁺)₂], respectively.
Following data are also provided for supporting the conclusions.
Im₂Cz, 1-ethyl-4,7-bis(2-(1-methylimidazol-2-yl)-ethynyl)-carbazole ( =56.7x10³ M cm^-1), 1H NMR (300 MHz, CD₃CN): 8.31 (s, 2H), 7.64 (d, J = 8.4 Hz, 2H), 7.49 (d, J = 8.4 Hz, 2H), 7.06 (s, 2H), 7.00 (s, 2H), 4.35 (q, J = 7.1 Hz, 2H), 3.76 (s, 6H), 1.33 (t, J = 7.1 Hz, 3H). Anal. Calcd. for C₂₆H₂₁N₅: C, 77.40; H, 5.25; N, 17.36. Found: C, 77.31; H, 4.98; N, 17.51. 13C NMR (100 MHz, CD₃CN): 141.42, 133.28, 130.62, 129.95, 125.35, 123.25, 123.02, 118.26, 113.23, 110.72, 94.00, 78.33, 38.71, 34.01, 14.05 ppm. HRMS (ESI-MS) m/z Calcd. for C₂₆H₂₁N₅ [M]+: 404.1875, found 404.1874. ESI-MS signals m/z = 1019.23 (m/z = 1019.24 calcd. for {[Zn(Im₂Cz)₂](OSO₂CF₃)}⁺) and m/z = 1784.25 (m/z =1784.25 calcd. for {[Zn₂ (Im₂Cz)₃](OSO₂CF₃)₃}⁺) were observed in acetone solutions, [Im₂Cz]_total = 2.1 x 10^-3 mol dm^-3 with [Zn²⁺]_total = 1.2 x 10^-3 mol dm^-3 and 2.8 × 10^-3 mol dm^-3, respectively.

Fig. C1 Observed UV-vis absorption spectral changes upon addition of Zn²⁺ [0 mol dm^-3 (red line) - 7.8 x 10^-5 mol dm^-3 (green line) - 1.6 x 10^-4 mol dm^-3 (blue line)] to a MeCN solution of Im₂Cz (1.5 x 10^-4 mol dm^-3) at 298 K (1 mm path length). Inset: Plot of absorbance at lambda = 365 nm vs. [Zn²⁺]/[Im₂Cz]₀, where [Im₂Cz]₀ is the initial concentration of Im₂Cz (1.5 x 10^-4 mol dm^-3).

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