Cyclodextrin Rotaxanes of Pt Complexes and Their Conversion to Pt Nanoparticles

The cationic Pt complex (Pt(NC₆H₄-C₆H₄N-(CH₂)₁₀-O(C₆H₃-3,5-(OMe)₂)(MeN-(CH₂CH₂NMe₂)₂))⁺ was prepared by the reaction of alkylbipyridinium ligand with a nitrateplatinum(II) complex. Mixing the complex and α- and β-cyclodextrins in aqueous media produced the corresponding [2]rotaxanes with 1:1 stoichiometry. γ-Cyclodextrin and the Pt complex formed a rotaxane having components in a 1:1 or 2:1 molar ratio. The results of mass and nuclear magnetic resonance (NMR) measurements confirmed the rotaxane structures of the Pt complexes. Transmission electron microscopy (TEM) and atomic force microscope (AFM) analyses revealed the formation of micelles or vesicles. The addition of NaBH₄ to the rotaxanes in aqueous media formed Pt nanoparticles with diameters of 1.3-2.8 nm, as characterized by TEM. The aggregated size of the nanoparticles formed from the rotaxane did not change even at 70 °C, and they showed higher thermal stability than those obtained from the reduction of the cyclodextrin-free Pt complex.