Synthesis, Characterization, and Surface Tethering of Sulfide-Functionalized Ti16-oxo-alkoxy Cages

• Published in: Chemistry of materials 2010-09, Vol.22 (18), p.5174-5178
• Main Authors: Eslava, Salvador, Papageorgiou, Anthoula C, Beaumont, Simon K, Kyriakou, Georgios, Wright, Dominic S, Lambert, Richard M
• Format: Article
• Language: eng ; jpn
• Subjects: Coatings, Thin films, and Monolayers; Nanomaterials (Nanops, Nanotubes, etc.); Surface and Interfacial Phenomena
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm101039k

The parent cage [Ti16O16(OEt)32] readily undergoes ligand exchange with a range of primary alcohols to yield species of the type [Ti16O16(OEt)32−x (OR′) x ], with R′ = Me, n-Pr, and n-Bu with x of up to 8. Attempted ligand exchange using the thiol [HO(CH2)4SH] in an attempt to produce functionalized cages suitable for tethering to Au surfaces failed, resulting only in the polymerization of the Ti oxo-cores. However, the use of the thioether [HO(CH2)4SCH3] resulted in successful thio-functionalization and preservation of the Ti16 cage core, likely due to methyl protection on the sulfide which precludes further intermolecular reaction with other cage molecules. ESI-MS and NMR showed that the resulting substituted cage [Ti16O16(OEt)24{O(CH2)4SCH3}8] contained eight methylthio-n-butoxy ligands in two groups of four pseudoequivalent positions. High resolution XPS and STM demonstrated that this sulfide-functionalized cage underwent covalent tethering to Au surfaces involving five sulfur linkages per cage, forming a monolayer of adsorbed species in which the molecular integrity had been preserved. In contrast, the parent oxo-alkoxy cage underwent extensive decomposition, rendering it useless as a building block for specific surface architectures.