In situ gel-to-crystal transition and synthesis of metal nanoparticles obtained by fluorination of a cyclic β-aminoalcohol gelator

Abstract

A new fluorinated version of a cyclic β-aminoalcohol gelator derived from 1,2,3,4-tetrahydroisoquinoline is presented. The gelator is able to gel various nonprotic solvents through OH×××N hydrogen bonds and additional CH×××F interactions due to the introduction of fluorine. A bimolecular lamellar structure is formed in the gel phase, which partly preserves the pattern of molecular organization in the single crystal. The racemate of the chiral gelator shows lower gelation ability than its enantiomer because of a higher tendency to form microcrystals, as shown by X-ray diffraction analysis. The influence of fluorination on the self-assembly of the gelator and the properties of the gel was investigated in comparison to the original fluorine-free gel system. The introduction of fluorine brings two new features. The first is good recognition of o-xylene by the gelator, which induces an in situ transition from gels of o-xylene and of an o-xylene/toluene mixture to identical single crystals with unique tubular architecture. The second is the enhanced stability of the toluene gel towards ions, including quaternary ammonium salts, which enables the preparation of a stable toluene gel in the presence of chloroaurate or chloroplatinate. The gel system can be used as a template for the synthesis of spherical gold nanoparticles with a diameter of 5 to 9 nm and wormlike platinum nanostructures with a diameter of 2 to 3 nm and a length of 5 to 12 nm. This is the first example of a synthesis of platinum nanoparticles in an organogel medium. Therefore, the appropriate introduction of a fluorine atom and corresponding nonbonding interactions into a known gelator to tune the properties and functions of a gel is a simple and effective tactic for design of a gel system with specific targets. Just add fluorine: Fluorination of a gelator brings new features to the resulting gel, that is, the in situ gel-to-crystal transition for selective recognition of o-xylene by the gelator, which indicates the structural evolution of the gel architecture, and also the synthesis of Au and Pt nanoparticles by using a toluene gel as a template that provides enhanced stability towards the ions (see figure; TOA-Au=(C8H17)4N+[AuCl 4]-; TOA-Pt=(C8H17) 4N+[PtCl6]-). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.