Three‐Dimensional Solvent‐Vapor Map Generated by Supramolecular Metal‐Complex Entrapment

Supramolecular assemblies have become increasingly popular over the past few years, especially in areas such as catalysis, gas sequestration, and separation. Similarly, interesting approaches for the detection of toxic gases and vapors of volatile organic compounds (VOCs) have been studied to develop an artificial nose that is capable of identifying these species in an unambiguous and simple way. The use of supramolecular and crystalline arrays of metal complexes with electronic transitions that are sensitive to the presence of a variety of volatile molecules, has received considerable attention. However, although metal complexes of platinum, gold, palladium, and copper have been widely employed for vapor detection, rhenium has been rarely used. Herein, we propose to use a zeolite framework for the supramolecular assembly of rhenium complexes with applications to vapor sensing. Zeolites are aluminosilicates with a repeating microporous structure composed of {AlO4} and {SiO4} building blocks. The internal framework is a network of cavities (supercages) that are interconnected by channels (Figure 1a). This architecture allows zeolites to act as molecular sieves, with applications ranging from catalysis to light-harvesting systems. Because of their porous structure, ion-exchange properties, and molecular and size recognition, many ions and molecules have been immobilized within zeolites. Particularly relevant for this research, the photoluminescent tris(2,2’-bipyridine)ruthenium(II) complex ([Ru(bpy)3] ) has been encapsulated in NaY and thoroughly studied. As the pore diameter of the NaY framework is smaller than the diameter of [Ru(bpy)3] , this molecule is synthesized in situ by a ship-in-the-bottle method. This method involves the loading of NaY with a ruthenium salt, followed by the addition of 2,2’-bipyridine as a ligand. The [Ru(bpy)3] 2+ complex is formed inside the supercage, and therefore it becomes entrapped within the zeolite. The material is fundamentally composed of a zeolite framework, with the supercages occupied by individual [Ru(bpy)3] 2+ ions, thus forming a true solid solution. Inspired by the aforementioned reports, we used the shipin-the-bottle method to synthesize [Re(phen)(CO)3Cl] (phen= 1,10-phenanthroline) in the cavities of the NaY zeolite. The ligands and the metal react in the NaY supercages to form the [Re(phen)(CO)3Cl] complex. The supercages of the NaY zeolite have a diameter of approximately 13 (large enough to accommodate the complex with a diameter of ca. 9 ) and pore entrances of approximately 7.4 . Therefore, the rhenium complex can fit into the supercage, but once it has been entrapped inside, it is too large to diffuse out of the cage through the pore entrance. To the best of our knowledge, Figure 1. Effect of solvent vapors on the photophysical properties of [Re(phen)(CO)3Cl]@NaY. a) Representation of the NaY zeolite showing one of the supercavities where [Re(phen)(CO)3Cl] can be entrapped. b) Photoluminescence spectra of [Re(phen)(CO)3Cl]@NaY upon treatment with different solvent vapors showing the change in emission intensity (no vapor: material before exposure to vapor, with a photoluminescence adjusted to unity). c) The normalized photoluminescence, which was obtained from the spectra in (b), emphasizes the change in photoluminescence maxima with different vapors. d) Timeresolved photoluminescence decays of [Re(phen)(CO)3Cl]@NaY under different solvent vapors. e) Digital photographs of vapor-treated [Re(phen)(CO)3Cl]@NaYmaterial under UV light. DMF=N,N-dimethylformamide, DMSO=dimethyl sulfoxide.