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Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies

[Image: see text] We present an in-depth mechanistic study of the first steps of the solution-based synthesis of the peculiar hexagonal tungsten bronze-type Ti(OH)OF·0.66H(2)O solid, using NMR analyses ((1)H, (13)C, (19)F, and (11)B) as well as modeling based on density functional theory (DFT) and a...

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Autores principales: Sieland, Melanie, Schenker, Manuel, Esser, Lars, Kirchner, Barbara, Smarsly, Bernd M.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8851441/
https://www.ncbi.nlm.nih.gov/pubmed/35187350
http://dx.doi.org/10.1021/acsomega.1c06534
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author Sieland, Melanie
Schenker, Manuel
Esser, Lars
Kirchner, Barbara
Smarsly, Bernd M.
author_facet Sieland, Melanie
Schenker, Manuel
Esser, Lars
Kirchner, Barbara
Smarsly, Bernd M.
author_sort Sieland, Melanie
collection PubMed
description [Image: see text] We present an in-depth mechanistic study of the first steps of the solution-based synthesis of the peculiar hexagonal tungsten bronze-type Ti(OH)OF·0.66H(2)O solid, using NMR analyses ((1)H, (13)C, (19)F, and (11)B) as well as modeling based on density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation. The reaction uses an imidazolium-based ionic liquid (IL, e.g., C(x)mim BF(4)) as a solvent and reaction partner. It is puzzling, as the fluorine-rich crystalline solid is obtained in a “beaker chemistry” procedure, starting from simple compounds forming a stable solution (BF(4)(–)-containing IL, TiCl(4), H(2)O) at room temperature, and a remarkably low reaction temperature (95 °C) is sufficient. Building on NMR experiments and modeling, we are able to provide a consistent explanation of the peculiar features of the synthesis: evidently, the hydrolysis of the IL anion BF(4)(–) is a crucial step since the latter provides fluoride anions, which are incorporated into the crystal structure. Contrary to expectations, BF(4)(–) does not hydrolyze in water at room temperature but interacts with TiCl(4), possibly forming a TiCl(4) complex with one or two coordinated BF(4)(–) units. This interaction also prevents the heavy hydrolysis reaction of TiCl(4) with H(2)O but—on the other side—spurs the hydrolysis of BF(4)(–) already at room temperature, releasing fluoride and building F-containing Ti(OH)(x)Cl(4–x)F(y) complexes. The possible complexes formed were analyzed using DFT calculations with suitable functionals and basis sets. We show in addition that these complexes are also formed using other titanium precursors. As a further major finding, the heating step (95 °C) is only needed for the condensation of the Ti(OH)(x)Cl(4–x)F(y) complexes to form the desired solid product but not for the hydrolysis of BF(4)(–). Our study provides ample justification to state a “special IL effect”, as the liquid state, together with a stable solution, the ionic nature, and the resulting deactivation of H(2)O are key requirements for this synthesis.
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spelling pubmed-88514412022-02-18 Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies Sieland, Melanie Schenker, Manuel Esser, Lars Kirchner, Barbara Smarsly, Bernd M. ACS Omega [Image: see text] We present an in-depth mechanistic study of the first steps of the solution-based synthesis of the peculiar hexagonal tungsten bronze-type Ti(OH)OF·0.66H(2)O solid, using NMR analyses ((1)H, (13)C, (19)F, and (11)B) as well as modeling based on density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation. The reaction uses an imidazolium-based ionic liquid (IL, e.g., C(x)mim BF(4)) as a solvent and reaction partner. It is puzzling, as the fluorine-rich crystalline solid is obtained in a “beaker chemistry” procedure, starting from simple compounds forming a stable solution (BF(4)(–)-containing IL, TiCl(4), H(2)O) at room temperature, and a remarkably low reaction temperature (95 °C) is sufficient. Building on NMR experiments and modeling, we are able to provide a consistent explanation of the peculiar features of the synthesis: evidently, the hydrolysis of the IL anion BF(4)(–) is a crucial step since the latter provides fluoride anions, which are incorporated into the crystal structure. Contrary to expectations, BF(4)(–) does not hydrolyze in water at room temperature but interacts with TiCl(4), possibly forming a TiCl(4) complex with one or two coordinated BF(4)(–) units. This interaction also prevents the heavy hydrolysis reaction of TiCl(4) with H(2)O but—on the other side—spurs the hydrolysis of BF(4)(–) already at room temperature, releasing fluoride and building F-containing Ti(OH)(x)Cl(4–x)F(y) complexes. The possible complexes formed were analyzed using DFT calculations with suitable functionals and basis sets. We show in addition that these complexes are also formed using other titanium precursors. As a further major finding, the heating step (95 °C) is only needed for the condensation of the Ti(OH)(x)Cl(4–x)F(y) complexes to form the desired solid product but not for the hydrolysis of BF(4)(–). Our study provides ample justification to state a “special IL effect”, as the liquid state, together with a stable solution, the ionic nature, and the resulting deactivation of H(2)O are key requirements for this synthesis. American Chemical Society 2022-02-02 /pmc/articles/PMC8851441/ /pubmed/35187350 http://dx.doi.org/10.1021/acsomega.1c06534 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Sieland, Melanie
Schenker, Manuel
Esser, Lars
Kirchner, Barbara
Smarsly, Bernd M.
Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title_full Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title_fullStr Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title_full_unstemmed Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title_short Ionic Liquid-Based Low-Temperature Synthesis of Crystalline Ti(OH)OF·0.66H(2)O: Elucidating the Molecular Reaction Steps by NMR Spectroscopy and Theoretical Studies
title_sort ionic liquid-based low-temperature synthesis of crystalline ti(oh)of·0.66h(2)o: elucidating the molecular reaction steps by nmr spectroscopy and theoretical studies
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8851441/
https://www.ncbi.nlm.nih.gov/pubmed/35187350
http://dx.doi.org/10.1021/acsomega.1c06534
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