ABSTRACT
Single Wall Carbon Nanotubes (SWCNT) prepared by the "super growth" method and arc-grown material were used as templates for peapod preparation with La@C(82). A qualitative change of the electron paramagnetic resonance (EPR) properties of La@C(82) is observed after incorporation into SWNT. The loss of lanthanum hyperfine interaction in combination with the observed increase of EPR susceptibility by two orders of magnitude after peapod preparation when comparing with signals from "empty" tubes is indicative for the generation of itinerant spins by charge and spin transfer from La@C(82) to the tubes. This interpretation is supported by the observation of fast spin dephasing, detected with pulsed EPR techniques.
ABSTRACT
The double-bridged hemicarcerand [A,B-(CH2OH)2-cavitand]-(CH2NHCH2)2-[A,B-(CH2OH)2-cavitand] 23 (and several other related compounds) was synthesized by the condensation of the two complementary precursors A,B-(CH2NH2)2(CH2OH)2-cavitand and A,B-(CH2Br)2(CH2OAc)2-cavitand followed by hydrolysis of the acetate groups. This hemicarcerand has nitrogen and oxygen donor atoms located on the interior of the spherical cavity and thus allows endohedral coordination of metal ions. The cavity has a volume of approximately 0.12 nm3, a value obtained by calculating a Connolly-type contact surface and the molecular electrostatic potential. The Cu2+ complex of hemicarcerand 23 was studied in detail by EPR and DFT calculations at the UB3LYP/6-31G level to verify the anticipated endohedral nature of the metal complex. It could be shown that the copper ion is coordinated to four oxygen donor atoms and no deviation from axial symmetry at the copper site could be detected. No direct coordination to nitrogen atoms of the hemicarcerand could be observed; however, complexation with DMF solvent molecules was detected by ESEEM and HYSCORE experiments. The closed structure of the hemicarcerand was also confirmed by an evaluation of proton-copper distances. Results from DFT calculations are in accord with the EPR results, and further support suggested coordination of the Cu(II) within the hemicarcerand cavity by four oxygen donor atoms.
ABSTRACT
Endohedral fullerenes N@C(60) and N@C(70) were dissolved in the liquid crystal 4-methoxybenzylidene-4'-n-butylaniline (MBBA) and investigated by electron paramagnetic resonance. In both cases well resolved EPR spectra give proof for molecular orientation in the nematic mesophase. Spectral features are dominated by a nonvanishing zero-field interaction, indicating a deviation from spherical spin density distribution at the encased nitrogen atom. In N@C(70), a maximum order parameter O(33) = 0.18(3), correlated with the long axis of the cage, and a zero-field-splitting parameter D = -2.6(4) MHz were determined. A persistent zero-field splitting is also observed in C(60) via the quartet spin of the encapsulated nitrogen, although no assignment of the director with respect to the molecular frame is possible. The observed line splitting is indicative of pseudo orientation of the rapidly rotating cage in this case.
