Alkali Intercalated Rhombohedral C 60 Polymers

1. Alkali Intercalated Rhombohedral C60 Polymers D. Pontiroli, M. Riccò, M. Belli, A. Goffredi

2. Aim of this work WP 4-Task 4.4: Intercalation of alkali and alkaline earth elements in C60 polymers • Spin transfer from the donor atom to the fullerene (as in TDAE-C60) • The small inter-fullerene distance of the polymer should promote the exchange interaction The doping process must preserve the polymeric (rhombohedral) structure

3. Outline • Characterisation of the precursors Rh-C60 (RES-5) XRD structure check Depolymerisation temperature • Intercalation by thermal decomposition of alkali azides • Intercalation by alkali solution in liquid NH3 The (NH3)6LixC60 phase (3x6) • Some considerations • Conclusions

4. Rhombohedral C60 Rh-C60 provided by RES-5: samples 945, 1000, 1002, 1003 • Pellets (50100 mg) • Exposed to air • Preliminary magneticSQUIDcharacterisation No intrinsic magnetism!

5. Observed Calculated Residual Intensity (a.u.) 10 15 20 25 30 35 40 45 2 (degrees) XRD check of the samples All the reflections of the Rh-poly structure were indexed N. Regueiro et al., Phys. Rev. Lett.74 (2), 1995, p. 278 Sample 1000 S. G.: R 3 m a = b = 9.28(4) Å, c = 24.29(4) Å,  = 120°

6. 220°C 200°C 180°C 160°C Intensity (a. u.) 140°C 120°C 100°C 25°C 10 15 20 25 30 Angle 2 (degrees) Depolymerisation temperature Laboratory XRD analysis (CuK) during heating treatment yields the depolymerisation temperature of the samples • The transition to the monomer state is irreversible • Tdepol depends on the sample • Standard intercalation methods are not suitable

7. 300 10-3 250 200 10-4 Pressure (mbar) 150 Temperature (°C) 10-5 100 50 10-6 0 25 0 5 10 15 20 Time (hours) Li intercalation with azides LixC60 is obtained by thermal decomposition of LiN3 mixed to pristine C60 C60 + x· LiN3 LixC60 + 3/2 · x · N2  • High efficiency • Relatively low reaction temperature (Tdec~430 K for LiN3)

8. -Li4C60 CuK Intensity (a. u.) 10 20 30 40 50 60 2 (degrees) Li intercalation with azides LixC60 is obtained by thermal decomposition of LiN3 mixed to pristine C60 C60 + x· LiN3 LixC60 + 3/2 · x · N2  • High efficiency • Relatively low reaction temperature (Tdec~430 K for LiN3) • Highly homogeneous samples • No presence of unreacted reagents

9. 200 10-5 150 100 Pressure (mBar) 10-5.5 Temperature (°C) 50 10-6 0 0 5 10 15 20 Time (hours) Li3 Rh-C60 We tried to intercalate Rh-C60 (sample 945) with the same method, after modifying the thermal program • Temperature was kept below 440 K • Not optimal decomposition of LiN3

10. Li3 Rh-C60 We tried to intercalate Rh-C60 (sample 945) with the same method, after modifying the thermal program • Temperature was kept below 440 K Li3 Rh-C60 • Not optimal decomposition of LiN3 CuK Intensity (a. u.) • Presence of two phases: monomer C60and Rh-C60 Local HT azide decomposition? 10 15 20 25 30 35 40 45 2 (degrees)

11. Magnetic response of Li3 Rh-C60 Li3 Rh-C60 underwent SQUID measurements and the magnetic response was compared with that of the precursor Rh-C60 (945) • The magnetic moment increases after Li intercalation 15 300 K, after interc. 300 K, before interc. (945) 10 FM impurities (Fe): 19g / g before 62g / g after 5 mol (emu/mol) 0 -5 Further investigation is required! -10 -2 -1 0 1 2 Applied Field (T)

12. Li intercalation by solution in NH3 Alkali metals solve in liquid ammonia and C60 can enter in solution and react with them D. R. Buffinger et al., J. Am. Chem. Soc.115, 1993, p. 9267 • Very low reaction temperature (T~240 K) • Ammonia simply acts as a spacer without interfering with the charge transfer • Excess of NH3 is pumped out from the product

13. Li3 Rh-C60 : NH3 CuK Intensity (a. u.) 10 20 30 40 50 2(degrees) Li3 Rh-C60 in liquid NH3 Rh-C60 (sample 1000) reacted with lithium solution in liquid NH3 for 3 hours at 240 K (stoich. ratio 1 : 3) • Temperature was always kept below depolymerisation threshold • XRD analysis on the product perfectly matches with the structure of the well known compound (NH3)6LixC60

14. Structure of (NH3)6Li3C60 (NH3)6LixC60 (3x6) has a bcc structure in which lithium is linearly coordinated to two ammonia molecules P. Durand et al., Nat. Mater.2, 2003, p. 605 • S. G.: I m 3 • a = 10.9230(7) Å for x = 3 • C60 distance of ~10.33 Å compatible with fullerenes in monomer state Li N Charge transfer effect?

15. 40 300 K, after interc. 35 300 K before interc. (1000) 30 25 20 mol(emu/mol) 15 10 5 0 -5 0 0.5 1 1.5 2 2.5 Applied Field (T) Magnetic response of Li3C60-Rh : NH3 Li3 Rh-C60 : NH3 underwent SQUID measurements and the magnetic response was compared with that of the precursor Rh-C60 (1000) • Again the magnetic moment increases after intercalation FM impurities (Fe): 73 g / g before 192g / g after

16. Considerations In both cases, the presence of a donor intercalant like lithium seems to destroy the polymerisation of the neutral rhombohedral fullerite used as a precursor, despite the small dimensions of the alkali ion Although the treatment yielded an increase of magnetic moment, we did not manage to intercalate Rh-C60!

17. Conclusions • Use of LiN3 is not suitable for the production of lithium intercalated rhombohedral C60 • Doping Rh-C60 with alkali solution in liquid NH3 at 240 K yields the known compound (NH3)6LixC60, which is in the monomer form • The charge state of Rh-C60seems not to be compatible with its polymerised structure • In both cases an increase of the magnetic moment of the samples was observed, but further analyses are required Thank you for your attention!