Nature of the Interaction and Photophysical Properties of [Mo6Cli8(SO3CF3)a6]2- and [Mo6Cli8Cla6]2- on Silica Gel

L. M. Robinson, H. Lu, J. T. Hupp, D. F. Shriver

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Abstract

The nature of the interaction between silica gel and [Mo6Cli8(SO3CF3)a6]2- (1) and [Mo6Cli8Cla6]2- (2) in organic media is described. Silica gel, which contains a high density of Si-OH groups, strongly adsorbs clusters 1 and 2. Although 1 is adsorbed from CH2Cl2 and solvents of high dielectric constant, such as CH3OH, 2 is adsorbed only from CH2Cl2 solution. In CH2Cl2, basic silica gel, containing a small percentage of anionic Si-O- sites, coordinates with Mo atoms of 1 by replacement of labile trillate groups. In more polar solvents, such as CH3OH and CH3CN, the triflate ligands of 1 are replaced by solvent molecules to produce [Mo6Cli8(solvent)a6]4+, which can then covalently attach to the silica gel surface. Presumably, Si-OH ionization is promoted in these polar media to yield SiOsurface sites. Under the same conditions, the less substitutionally labile cluster, [Mo6Cli8Cla6]2-, is not covalently attached to silica gel. The supported systems are stable to atmospheric moisture and O2 but undergo decomposition in the presence of liquid water. Clusters bound by either electrostatic or covalent interaction display absorption and emission profiles virtually identical to those of solution species, indicating that the clusters are intact. Transient emission measurements reveal that supported 1 retains the characteristic longlived excited state in 1 in solution: τgel = 100 µs and τsoin = 110 µs. The photochemical properties of the silica gel bound molybdenum cluster are retained, as indicated by luminescence quenching by O2 and phenothiazine.

Original languageEnglish
Pages (from-to)43-49
Number of pages7
JournalChemistry of Materials
Volume7
Issue number1
DOIs
Publication statusPublished - Jan 1995

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ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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