Synthesis and electronic and magnetic properties of new endohedral fullerenes with hybrid lanthanidetransition metal clusters
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
The project was focused on the synthesis, isolation, and comprehensive studies of electronic and magnetic properties of endohedral metallofullerenes (EMFs) comprising lanthanides and a transition metals in the inner cluster. A series of metal-carbide clusterfullerenes M2TiC@C80 (M = Sc, Y, Ce, Nd, Gd, Dy, Er, and Lu) is synthesized successfully, and the influence of the metal size on the production yield is clarified. A method for selective synthesis of such compounds based on the use of methane as a reactive gas is developed, which substantially simplifies chromatographic separation routines as these EMFs are the main products of the arc-discharge synthesis. The use of methane also allowed discovery of new species with one more carbon atom in the cluster, M2TiC2@C80. Single-crystal X-ray diffraction studies are performed for Sc2TiC@C80 and Lu2TiC@C80, and the presence of the double bond between endohedral carbon and Ti atoms is confirmed. Molecular structures of M2TiC2@C80 compounds was elucidated by 13C NMR spectroscopy. Systematic electrochemical study of M2Ti@C80 compounds revealed strong dependence of the reduction potential on the metal M. Computational studies showed that the LUMO is localized on Ti, which therefore changes its oxidation state upon reduction. This change is accompanied by the increase of Ti ionic radius, which is responsible for the metal-size dependence of the redox potentials. Magnetometry studies showed that Dy2TiC@C80 behaves as a single molecule magnet (SMM), however with lower blocking temperature of magnetization than in the isostructural and isoelectronic Dy2ScN@C80. Addition of one more carbon atoms to the endohedral cluster deteriorates magnetic properties substantially, and Dy2TiC2@C80 is a very weak SMM. Detailed studies of magnetic properties were also performed for a series of other lanthanide clusterfullerenes. Detailed studies of the role of methane in the synthesis of carbide clusterfullerenes are performed fort Sc/Ti/CH4 system. The use of 13C-enriched reagents in the synthesis of EMFs (either 13CH4 or 13C- graphite) and subsequent mass-spectrometric and NMR analysis shed the light on the mechanism of carbide clusterfullerenes formation. In addition to the study of the reaction mechanism, this work also afforded the synthesis of Sc3CH@C80 in much higher amount than previously and perform its structural characterization. New EMFs structures with odd number of carbons, such as Sc4C3@C80 and Sc4C@C80, were detected. Finally, molecular dynamics simulations of the endohedral fullerene formation in carbon/metal/helium vapor are performed, the mechanism of the metal encapsulation is revealed, and important role of the reactor atmosphere (helium, presence of hydrogen) is revealed.
Publications
- "A redox-active scandium-oxide cluster inside a fullerene cage: Spectroscopic, voltammetric, ESR spectroelectrochemical and extended DFT study of Sc4O2@C80 and its ion-radicals". J. Am. Chem. Soc. 2012, 134 (48), 19607–19618
A. A. Popov, N. Chen, J. R. Pinzón, S. Stevenson, L. A. Echegoyen, L. Dunsch
(See online at https://doi.org/10.1021/ja306728p) - "Bonding between strongly repulsive metal atoms: an oxymoron made real in a confined space of endohedral metallofullerenes." Chem. Commun. 2012, 48, 8031-8050
A. A. Popov, S. M. Avdoshenko, A. M. Pendás, L. Dunsch
(See online at https://doi.org/10.1039/c2cc32568c) - "Endohedral Fullerenes". Chem. Rev. 2013, 113 (8), 5989–6113
A. A. Popov, S. Yang, L. Dunsch
(See online at https://doi.org/10.1021/cr300297r) - "Strain-Driven Endohedral Redox Couple CeIV/CeIII in Nitride Clusterfullerenes CeM2N@C80 (M = Sc, Y, Lu)." J. Phys. Chem. Lett. 2013, 4, 2404-2409
Y. Zhang, S. Schiemenz, A. A. Popov, L. Dunsch
(See online at https://doi.org/10.1021/jz4009773) - "Clusters encapsulated in Endohedral Metallofullerenes: How strained are they?" J. Am. Chem. Soc. 2014, 136 (11), 4257-4264
Q. Deng, A. A. Popov
(See online at https://doi.org/10.1021/ja4122582) - "Endohedral fullerene with μ3-carbido ligand and Titanium-Carbon double bond stabilized inside a carbon cage." Nat. Commun. 2014, 5, 3568
A. L. Svitova, K. B. Ghiassi, C. Schlesier, K. Junghans, Y. Zhang, M. M. Olmstead, A. L. Balch, L. Dunsch, A. A. Popov
(See online at https://doi.org/10.1038/ncomms4568) - "Magnetic Anisotropy of Endohedral Lanthanide Ions: Paramagnetic NMR Study of MSc2N@C80-Ih with M running through the Whole 4f Row." Chem. Sci. 2015, 6, 2328-2341
Y. Zhang, D. Krylov, M. Rosenkranz, S. Schiemenz, A. A. Popov
(See online at https://doi.org/10.1039/c5sc00154d) - "Methane as a selectivity booster in the synthesis of endohedral fullerenes: towards selective synthesis of the single molecule magnet Dy2TiC@C80 and its congener Dy2TiC2@C80". Angew. Chem. Int. Ed. 2015, 54 (45), 13411-13415
K. Junghans, C. Schlesier, A. Kostanyan, N. A. Samoylova, Q. Deng, M. Rosenkranz, S. Schiemenz, R. Westerström, T. Greber, B. Büchner, A. A. Popov
(See online at https://doi.org/10.1002/anie.201505870) - "Synthesis and Structure of LaSc2N@Cs(hept)‐C80 with One Heptagon and Thirteen Pentagons." Angew. Chem. Int. Ed. 2015, 54 (2), 495-499
Y. Zhang, K. B. Ghiassi, Q. Deng, N. Samoylova, M. M. Olmstead, A. L. Balch, A. A. Popov
(See online at https://doi.org/10.1002/anie.201409094) - "Sc3CH@C80: selective 13C enrichment of the central carbon atom." Chem. Commun. 2016, 52, 6561-6564
K. Junghans, M. Rosenkranz, A. A. Popov
(See online at https://doi.org/10.1039/c5cc10025a) - "Self-Assembly of Endohedral Metallofullerenes: A Decisive Role of Cooling Gas and Metal-Carbon Bonding." Nanoscale 2016, 8, 3796-3808
Q. Deng, T. Heine, S. Irle, A. A. Popov
(See online at https://doi.org/10.1039/c5nr08645k) - "Synthesis and Isolation of the Titanium-Scandium Endohedral Fullerenes – Sc2TiC@Ih-C80, Sc2TiC@D5h-C80, and Sc2TiC2@Ih-C80: Metal Size Tuning of the TiIV/TiIII Redox Potentials." Chem. Eur. J. 2016, 22 (37), 13098–13107
K. Junghans, K. B. Ghiassi, N. A. Samoylova, Q. Deng, M. Rosenkranz, M. M. Olmstead, A. L. Balch, A. A. Popov
(See online at https://doi.org/10.1002/chem.201601655)
