Ideal Redox Behavior of the High-Density Self-Assembled Monolayer of a Molecular Tripod on a Au(111) Surface with a Terminal Ferrocene Group

A dyad consisting of a tripod-shaped trithiol with an adamantane core and a terminal ferrocenyl group linked through a <i>p</i>-phenyleneethynylene bridge was synthesized. The trithiol formed a stable self-assembled monolayer (SAM) on Au(111), wherein each molecule is bound to the surface by three-point adsorption using all sulfur atoms, with confirmation by PM-IRRAS and XPS analyses. Cyclic voltammetry of the SAM showed a line shape typical of an ideal adsorbed system, that is, a monolayer with negligible electrostatic interaction among the terminal ferrocenyl groups. Thus, a rare SAM was achieved, in which the component molecules were isolated from adjacent molecules without the coadsorption of nonelectroactive molecules

Distance-Dependent Paramagnet-Enhanced Nuclear Spin Relaxation of H₂@C₆₀ Derivatives Covalently Linked to a Nitroxide Radical

A series of H₂@C₆₀ derivatives covalently linked to a nitroxide radical has been synthesized. We report distance-dependent nuclear spin relaxivity of H₂ in these derivatives. The results clearly indicate that the relaxivity of H₂ is distance-dependent and in good agreement with the Solomon−Bloembergen equation, which predicts a 1/<i>r</i>⁶ dependence

Synthesis, Isomer Count, and Nuclear Spin Relaxation of H₂O@Open-C₆₀ Nitroxide Derivatives

H₂O@C₆₀ derivatives covalently linked to a nitroxide radical were synthesized. The ¹H NMR of the guest H₂O revealed the formation of many isomers with broad signals. Reduction to the diamagnetic hydroxylamines sharpened the ¹H NMR signals considerably and allowed for an “isomer count” based on the number of observed distinct signals. For H₂O@K-8, 17 positional isomeric nitroxides are predicted, not including additional numbers of regioisomers; indeed, 17 signals are observed in the ¹H NMR spectrum

ENDOR Evidence of Electron–H₂ Interaction in a Fulleride Embedding H₂

An endofulleropyrrolidine, with H₂ as a guest, has been reduced to a paramagnetic endofulleride radical anion. The magnetic interaction between the electron delocalized on the fullerene cage and the guest H₂ has been probed by pulsed ENDOR. The experimental hyperfine couplings between the electron and the H₂ guest were measured, and their values agree very well with DFT calculations. This agreement provides clear evidence of magnetic communication between the electron density of the fullerene host cage and H₂ guest. The <i>ortho-H</i>_<i>2</i>/<i>para-H</i>_<i>2</i> interconversion is revealed by temperature-dependent ENDOR measurements at low temperature. The conversion of the paramagnetic <i>ortho-H</i>_<i>2</i> to the diamagnetic <i>para-H</i>_<i>2</i> causes the ENDOR signal to decrease as the temperature is lowered due to the spin catalysis by the paramagnetic fullerene cage of the radical anion fulleride