Nuclear spin isomers of guest molecules in H ₂ @C ₆₀ , H ₂ O@C ₆₀ and other endofullerenes

Abstract

Spectroscopic studies of recently synthesized endofullerenes, in which H 2 , H 2 O and other atoms and small molecules are trapped in cages of carbon atoms, have shown that although the trapped molecules interact relatively weakly with the internal environment they are nevertheless susceptible to appropriately applied external perturbations. These properties have been exploited to isolate and study samples of H 2 in C 60 and other fullerenes that are highly enriched in the para spin isomer. Several strategies for spin-isomer enrichment, potential extensions to other endofullerenes and possible applications of these materials are discussed.

NMR Lineshapes and Scalar Relaxation of the Water‐Endofullerene H217O@C60

“…The relevant portion of the oxygen‐17 NMR spectrum of H 2 17 O@C 60 is shown in Figure . A similar spectrum was reported previously by Chen et al . A triplet with | J OH |=77.9 Hz is observed.…”

“…A triplet with | J OH |=77.9 Hz is observed. The 17 O peak is at −36.4 ppm referenced with respect to a sample of H 2 17 O water (signal resonance placed at 0 ppm), in agreement with the literature . The oxygen‐17 spectrum of H 2 17 O@C 60 was acquired with an acquisition time of 0.603 s and was processed without line broadening.…”

“…The relevant portion of the oxygen-17 NMR spectrumo f H 2 17 O@C 60 is shown in Figure 2. As imilar spectrum was reported previously by Chen et al [7] At riplet with j J OH j = 77.9 Hz is observed. The 17 Op eak is at À36.4 ppm referenced with respect to as ample of H 2 17 Ow ater (signal resonance placed at 0ppm), in agreementw ith the literature [7].T he oxygen-17 spectrumo fH 2 17 O@C 60 wasa cquired with an acquisition time of 0.603 sand wasprocessed withoutline broadening.…”

“…[1][2][3] The confined molecules behave as free rotors with aw ell defined energy level structure [4] and have been probedb ynumerous spectroscopic methods including infrared spectroscopy,inelastic neutron scattering, and nuclear magnetic resonance( NMR). [3,[5][6][7][8][9] Nuclear spin isomer interconversion has been studied, [5,8,10] and the dielectric constant of H 2 O@C 60 was found to depend on the ortho/para ratio of the confined molecules. [11] Endofullerenes provide as heltered environmentf or the inserted small molecules, with the confining arena limiting interactions with other molecules.…”

Nanolaboratories: physics and chemistry of small-molecule endofullerenes

“…The article by Turro and co-workers [11] ranges widely over the many different spectroscopic phenomena expected and observed for these molecular systems, with special attention paid to the observation of the spin isomers and their interconversion. Since the para spin isomer of H 2 has no net nuclear spin it does not provide an NMR signal.…”