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Updated: Jun 8, 2026

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
Published on: October 18, 2019
Insertion of indigo molecules in the sepiolite structure as evidenced by 1H-29Si heteronuclear correlation
Jésus Raya1, Jérôme Hirschinger, Sonia Ovarlez
1Institut de Chimie, UMR 7177 CNRS, Université de Strasbourg, BP 296, 67008 Strasbourg Cedex, France.
Abstract:
Despite the numerous studies of the famous indigo-based pigment Maya Blue, there are still many questions regarding the elucidation of its structure. Here, two-dimensional (2D) (1)H-(29)Si heteronuclear correlation (HETCOR) spectroscopy with frequency-switched Lee-Goldburg (FSLG) homonuclear decoupling is applied to sepiolite and sepiolite-indigo complexes. Owing to the high resolution in the (1)H dimension of the 2D (1)H-(29)Si HETCOR spectrum obtained by FSLG homonuclear decoupling, the assignment of the (29)Si cross-polarization magic-angle spinning (CPMAS) spectrum of sepiolite is clearly confirmed. Moreover, 2D (1)H-(29)Si FSLG-HETCOR spectroscopy gives the first direct evidence that some indigo molecules are inserted in the sepiolite structure whereas no interaction between indigo and the external side surface (silanol groups) is observed in the (29)Si CPMAS spectra. These results are consistent with the fact that indigo molecules interact with water coordinated to magnesium and suggest that Maya Blue made from sepiolite is not a surface complex.
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