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Skeletal Transformation of a Classical Fullerene C88 into a Non-Classical Fullerene Chloride C84Cl30 Bearing Quaternary Sequentially Fused Pentagons Fei Jin, Shangfeng Yang, Erhard Kemnitz, and Sergej I. Trojanov J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b01490 • Publication Date (Web): 24 Mar 2017 Downloaded from http://pubs.acs.org on March 26, 2017
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Skeletal Transformation of a Classical Fullerene C88 into a Non-Classical Fullerene Chloride C84Cl30 Bearing Quaternary Sequentially Fused Pentagons Fei Jin,a Shangfeng Yang,*a Erhard Kemnitz,*b and Sergey I. Troyanov*c a
Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC), Hefei 230026, China. b
Institute of Chemistry, Humboldt University Berlin Brook-Taylor.-Str.2, 12489 Berlin, Germany.
c
Department of Chemistry, Moscow State University, 119991 Moscow, Leninskie gory, Russia.
ABSTRACT: A classical fullerene is composed of hexagons and pentagons only, and its stability is generally determined by the Isolated-Pentagon-Rule (IPR). Herein, high-temperature chlorination of a mixture containing a classical IPR-obeying fullerene C88 resulted in isolation and X-ray crystallographic characterization of non-IPR, non-classical (NC) fullerene chloride C84(NC2)Cl30 (1) containing two heptagons. The carbon cage in C84(NC2)Cl30 contains 14 pentagons, 12 of which form two pairs of fused pentagons and two groups of quaternary sequentially fused pentagons, which have never been observed in reported carbon cages. All 30 Cl atoms form an unprecedented single chain of ortho attachments on the C 84 cage. A reconstruction of the pathway of the chlorination-promoted skeletal transformation revealed that the previously unknown IPR isomer C88(3) is converted into 1 by two losses of C2 fragments followed by two Stone-Wales rearrangements, resulting in the formation of very stable chloride with rather short C Cl bonds.
A classical fullerene is composed of hexagons and pentagons only. Most of the known pristine empty fullerenes found in the fullerene soot, including C60, C70, and the higher ones, C74–C108, follow the Isolated-Pentagon-Rule (IPR) which determines the stability of a fullerene. Such fullerenes usually form exohedral derivatives under complete preservation of cage connectivities.1 Several examples of cage surgery on C60 and C70 were reported, dealing with multi-step opening and, sometimes, closing of the fullerene cages.2 Recently, skeletal cage transformations of classical fullerenes in the course of high-temperature chlorination have been discovered, involving a StoneWales rearrangement (SWR); i.e., a rotation of a CC bond by ca. 90⁰, and the loss of a C2 fragment. Thus, a seven-step sequence of SWRs in D2-C76 resulted in a nonIPR C76Cl24 containing five pairs of fused pentagons.3a A cage shrinkage of C86(16) (isomer numeration in the parentheses is according to the spiral algorithm4) by single and double C2 losses produced non-classical (NC) chlorides C84(NC1)Cl30 and C82(NC2)Cl30, which contain respectively one and two heptagons in their carbon cages (as indicated by the numeral after NC).3b,c Isomers of higher fullerenes differ by their ability to undergo cage transformations. Of two known isomers of C86, nos. 16 and 17, the latter does not show any cage
transformation, thus giving IPR chlorides C86(17)Cl18/20/22 only.3d Up to now, skeletal cage transformation were also found to occur in some chlorinated fullerene isomers of C82,5a C88,5b C90,5c C96,5d C100,5e and C102.5f Except the sevenstep sequence of SWRs in C76(1),3a other known cage transformations proceed in one to three steps. In the favorable cases, the experimental structural data are available not only for the final chlorinated fullerene with a nonIPR or non-classical cage but also for a chloride of the starting IPR fullerene and, more rarely, for intermediates.5b,c When the structural data are obtained exclusively for the resulting chloride with the transformed cage, a reconstruction of the pathway from IPR fullerene is necessary, which, as a rule, is represented by the shortest pathways among many possible ones.3b,5b,e Detailed mechanisms of several cage transformations were suggested on the basis of theoretical quantum-chemical calculations for SWRs 3a,5a and C2 losses.5c,e Higher fullerene C88 possesses 35 IPR-obeying isomers. All previous experimental results confirm the presence of three isomers in the fullerene soot, C2-C88(7), Cs-C88(17), and C2-C88(33),6a which are also the most stable ones according to theoretical calculations.6b,c As unambiguous confirmations, several chloro and trifluoromethyl derivatives of these three isomers, such as C88(7)Cl12/24,7a
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C88(17)Cl22,3d,7a C88(33)Cl12/14,7a C88(7)(CF3)12/16,7b and C88(33)(CF3)16/18/20,7c have been isolated and structurally characterized by X-ray crystallography. At the same time, isomer C88(33) undergoes cage shrinkage at higher chlorination degrees, affording non-classical C86(NC1)Cl24/26 and C84(NC2)Cl26.5b
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2). Such a sequence of transformation steps implies that the resulting structure restores C2 symmetry after the second step. A similar situation of retaining the starting symmetry has been found in some known skeletal transformations of symmetrical cages such as Cs-C86(16),3c C2C88(33),5b and C2-C100(18).5e
Herein, we report a remarkable four-step skeletal cage transformation of a new C88 isomer, C2-C88(3). A combined C2 loss/SWR transformation resulted in C84(NC2)Cl30 with a non-classical, non-IPR cage containing two pairs of fused pentagons and two quartets of sequentially fused pentagons, which have never been observed in the reported carbon cages. Theoretical calculations revealed that the stability of chlorinated derivatives on the pathway from C88(3)Cl30 to the final C84(NC2)Cl30 increases in each of four transformation steps. A chromatographic (HPLC) fraction of C92 separated by HPLC from the fullerene extract contained a small admixture of C88 according to MALDI-TOF analysis (see Supporting Information S1 for more details). Ca. 0.1 mg of C92/C88 was chlorinated in ampoules with VCl4 and a drop of SbCl5 at 350⁰ for 4 weeks. After ampoule opening and washing with HCl and water, two types of crystals were found. An X-ray diffraction study with the use of synchrotron radiation revealed that plate-like crystals are the known chloride of C92, C92(38)Cl20/22, whereas the needlelike orange crystals represent a new compound, C84Cl30, with a very unusual molecular shape and a non-classical carbon cage containing two heptagons (Figure 1).8
Figure 1. Three mutually orthogonal views of the C2C84(NC2)Cl30 molecule from the X-ray data (a-c); projection b) is given along the two-fold axis. Cage heptagons are shown in blue, whereas fused pentagons are highlighted with red color. Projection d) shows the starting C2-C88(3) cage with the shape of a regular ellipsoid according to DFT calculations.
The choice between two possible pathways was made on the assumption that each transformation step should proceed energetically favorable, i.e., under formation of the most stable chlorinated molecules. Our DFT calculations of the formation energies 9 and the average CCl energy (or chlorination enthalpy per 1 Cl atom) of the chlorides on two alternative pathways revealed that the sequence of two C2Ls followed by two SWRs is more preferable than an alternative pathway beginning with two SWRs.
Taking into account the composition C92/C88 of the starting HPLC fraction used for chlorination, the formation of C92(38)Cl20/22 was rather expected. However, the presence of C84(NC2)Cl30 (1) in the chlorination products should be considered as a result of a cage transformation of C88. It is known that, in most cases, the formation of a heptagon is a consequence of a C2 loss (C2L), i,e., the removal of a 5:6 CC bond from a fullerene cage.5 Therefore, two heptagons in the carbon cage of C84(NC2)Cl30 are expected to form via removal of two 5:6 CC bonds from a C88 cage.
The most probable pathway of the skeletal transformation is shown in Figure 2 with the use of Schlegel diagrams. The chlorination pattern in the starting C88(3)Cl30 is represented by a single chain of adjacent attachments with 30 Cl atoms in the same positions as in the final C84(NC2)Cl30 molecule. In the first and the second transformation steps, two C2Ls occur sequentially on both ends of the chain, resulting in the intermediate C2C84(NC2)Cl30 (i), which contains two heptagons and 14 pentagons forming two pairs and two triples of fused pentagons. The arrangements of triple sequentially fused pentagons were also found in some non-IPR cages of higher and lower fullerene chlorides.5b,10 As in all reported cases, only one of two pentagon-pentagon edges is fully chlorinated whereas another bears one Cl atom.
A systematic search for a precursory cage among all IPR isomers of C88 revealed that the starting cage can be only isomer C2-C88(3) and two C2L and two SWR steps are necessary to obtain the cage of C2-C84(NC2)Cl30 found experimentally. Furthermore, the CC bonds involved in two SWRs as well as two C2Ls are located C2 symmetrically on the starting cage of C88(3). In addition, four transformations steps are permutable, i.e., they can proceed in any order in principle (see Supporting Information S2 for details). For the purpose of the choice among 24 possible pathways, it was supposed that two similar transformations, two SWRs or C2Ls, occur first followed by two others, thus resulting in only two alternative pathways, two SWRs followed by two C2Ls or vice versa (see Figure 2
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number of chlorinated sites of pentagon-pentagon fusions (from 0 to 12), which are energetically more favorable than usual sites of pentagon-hexagon-hexagon junctions. Note that the alternative pathway beginning with SWRs shows much smaller increase of CCl bond energy for the two first steps (-0.1 and +5.7 kJ mol1, respectively). It should be noted that the presence of heptagons, pairs and quartets of fused pentagons in the cage of 1 results in a strong irregularity of its molecular shape (Figure 1). In the chain of 30 adjacent Cl attachments, sp3-sp3 single CC bonds are significantly elongated to 1.533-1.619(7) Å (av. 1.573 Å ). The lengths of CCl bonds lie in the range of 1.759-1.806(5) Å (av. 1.787 Å ), i.e., they are noticeably shorter, than 1.81-1.82 Å found in most chlorinated fullerenes,12 which correlates well with the high relative energy of CCl bonds in 1. A detection of a new isomer of C88 in the fullerene soot is unexpected, because all three well known isomers nos. 7, 17, and 33 are the most stable ones with close relative formation energies according to reported theoretical calculations.6b,c Our DFT calculations9 gave relative formation energies of 3.0, 0.0, and 5.2 kJ mol1, respectively, whereas other IPR isomers of C88 are less stable by at least 24 kJ mol1. Among them, isomer C2-C88(3) has a relative formation energy of 38.5 kJ mol1, and can be regarded as rather unstable. Its presence in the fullerene soot can be explained by the specific distribution of pentagons on its carbon cage. As seen in the Schlegel diagram of C88(3) shown in Figure 2, any SWR in a pyracelene fragment on the cage will result in a non-IPR cage and is, therefore, energetically unfavorable. Thus, C2-C88(3) is a topological “single” among IPR isomers of C88, in contrast to a large topological family of 29 isomers including isomers nos. 17 and 33.4 If such an isomer exists at high temperatures in the fullerene mixture, it cannot be converted into more stable IPR isomers by means of SWRs during annealing at lower temperatures and therefore remains intact in the fullerene mixture. Probably, similar restrictions are responsible for the presence of some other very unstable “singles” such as D5h-C90(1),13a,b D3d-C96(3),13c and D5dC100(1)13d in the arc-discharge fullerene soot.
Figure 2. Schlegel diagram presentation of the most probable pathway from a chloride of C2-C88(3) to the experimentally found C2-C84(NC2)Cl30 (1) through intermediate (i) C1C86(NC1)Cl30, C1- and C2-C84(NC2)Cl30. Cage pentagons are highlighted with red color and cage heptagons are shown in blue. Black circles denote the positions of Cl atoms. For C2symmetrical molecules, the positions of two-fold axes are shown by small crosses. CC bonds to be removed or rotated in the next step are indicated by small ovals.
Two subsequent SWRs contribute to further fusion of pentagons so that the carbon cage in the final C2C84(NC2)Cl30 (1) contains two groups of quaternary sequentially fused pentagons, which have never been reported previously. Noteworthy, only one of three common edges is fully chlorinated in both groups. Our DFT calculations revealed that the compounds on the proposed transformation pathway are characterized by the increase of the chlorination enthalpy (per 1 Cl; kJ mol 1) relative to that of D3d-C60Cl30 taken as a standard.11a It increases from -6.6 for C88(3)Cl30 to +9.1, +24.9, +30.3, and +35.1 for C86(NC1)Cl30, C2-C84(NC2)Cl30 (i), C1-C84(NC2)Cl30, and C2-C84(NC2)Cl30, respectively. A negative value for C88(3)Cl3o is due to the fact that no stabilizing substructures (isolated double C=C bonds and/or benzenoid rings) are available within its carbon cage, whereas all nonchlorinated carbon atoms in D3d-C60Cl30 are involved in aromatic substructures.11b A substantial increase of the chlorination enthalpy is accounted for by the increasing
For the first sight, it seems somewhat surprising that an isomer of C88 was co-eluted with C92. We believe that the longer retention time of C88(3) in comparison with three other known isomers of C88 is a result of different shapes of isomeric cages. While isomers nos. 7, 17, and 33 possess rather spherical cages which are only slightly distorted, the cage of C88(3) is more elliptical (see Figure 1). Substantial increase of the elution times for isomers with strongly elliptical or even nanotubular shapes by using Cosmosil 5PYE or Buckyprep columns have been reported for some other fullerene isomers such as D2d-C84(4) and D2-C84(5) (co-eluted with C86),14 D5h-C90(1) (co-eluted with C92),13b and D5d-C100(1) (co-eluted with C106-C112).13d 3
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(2) a) Murata, M.; Murata, Y.; Komatsu, K. Chem. Commun. 2008, 6083-6094; b) Yu, Y.; Xu, L.; Huang, X.; Liang, S.; Gan, L.; Synlett. 2016, 27, 2123-2127. (3) a) Ioffe, I. N.; Goryunkov, A. A.; Tamm, N. B.; Sidorov, L. N.; Kemnitz, E.; Troyanov, S. I. Angew. Chem. Int. Ed., 2009, 48, 5904-5907; b) Ioffe, I. N.; Chen, C.; Yang, S.; Sidorov, L. N.; Kemnitz, E.; Troyanov, S. I. Angew. Chem. Int. Ed. 2010, 49, 4784-4787; c) Wei, T.; Yang, S.; Kemnitz, E.; Troyanov, S. I. Chem. Asian J. 2015, 10, 559-562; d) Wei, T.; Yang, S.; Troyanov, S. I. Chem. Eur. J. 2014, 20, 14198-14200. (4) Fowler, P. W.; Manolopoulos, D. E. An Atlas of Fullerenes, Clarendon, Oxford, 1995. (5) a) Ioffe, I. N.; Mazaleva, O. N.; Sidorov, L. N.; Yang, S.; Wei, T.; Kemnitz, E.; Troyanov, S. I. Inorg. Chem. 2012, 51, 11226-11228; b) Yang, S.; Wei, T.; Scheurell, K.; Kemnitz, E.; Troyanov, S. I. Chem. Eur. J. 2015, 21, 15138-15141; c) Ioffe, I. N.; Mazaleva, O. N.; Sidorov, L. N.; Yang, S.; Wei, T.; Kemnitz, E.; Troyanov, S. I. Inorg. Chem. 2013, 52, 13821-13823; d) Yang, S.; Wei, T.; Wang, S.; Ioffe, I. N.; Kemnitz, E.; Troyanov, S. I. Chem. Asian J. 2014, 9, 3102-3105; e) Ioffe, I. N.; Yang, S.; Wang, S.; Kemnitz, E.; Sidorov, L. N.; Troyanov, S. I. Chem. Eur. J. 2015, 21, 4904-4907; f) Yang, S.; Wei, T.; Wang, S.; Ignat’eva, D. V.; Kemnitz, E.; Troyanov, S. I. Chem. Commun. 2013, 49, 7944-7946. (6) a) Miyake, Y.; Minami, T.; Kikuchi, K.; Kainosho, M.; Achiba, Y. Mol. Cryst. Liq. Cryst. 2000, 340, 553-558; b) Slanina, Z.; Uhlik, F.; Yoshida, M.; Osawa, E. Full. Sci. Techn. 2000, 8, 417-432; c) Sun, G. Chem. Phys. Lett. 2003, 367, 26-33. (7) a) Wang, S.; Yang, S.; Kemnitz, E.; Troyanov, S. I. Chem. Asian J. 2016, 11, 77-80; b) Tamm, N. B.; Troyanov, S. I. Mendeleev Commun. 2016, 26, 141-142; c) Lanskikh, M. A.; Chang, K.; Tamm, N. B.; Kemnitz, E.; Troyanov, S. I. Mendeleev Commun. 2012, 22, 136-137. (8) Synchrotron X-ray data were collected at 100 K on a MAR225 CCD detector on BL14.3 at the BESSY II electron storage ring (Berlin, Germany). C84Cl30·[0.35VOCl2·0.36VO2Cl·0.53Cl2]: triclinic, P1, a = 17.2709(8), b = 19.3481(6), c = 22.494(1) Å , = 85.767(5), = 80.923(7), = 84.766(9)º, V = 7378.0(6) Å 3, Z = 4, R1/wR2 = 0.062/0.149 for 25196/29140 reflections and 2254 parameters. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre with CCDC No. 1530011. (9) a) Laikov, D. N. Chem. Phys. Lett. 1997, 281, 151-156; b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865. (10) Tan, Y.-Z.; Li, J.; Zhu, F.; Han, X.; Jiang, W.-S.; Huang, R.-B.; Zheng, Z.; Qian, Z.-Z.; Chen, R.-T.; Liao, Z.-T.; Xie, S.-Y.; Lu, X.; Zheng, L.-S. Nat. Chem., 2010, 2, 269-273. (11) a) Papina, T. S.; Luk’yanova, V. A.; Troyanov, S. I.; Chelovskaya, N. V. ; Buyanovskaya, A. G. ; Sidorov, L. N. Russ. J. Phys. Chem. A 2007, 81, 159-163; b) Troshin, P. A.; Lyubovskaya, R. N.; Ioffe, I. N.; Shustova, N. B.; Kemnitz, E.; Troyanov, S. I. Angew. Chem. Int. Ed. 2005, 44, 234-237. (12) Troyanov, S. I.; Kemnitz, E. Curr. Org. Chem. 2012, 16, 10601078. (13) a) Yang, H.; Beavers, C. M.; Wang, Z.; Jiang, A.; Liu, Z.; Jin, H.; Mercado, B. Q.; Olmstead, M. M.; Balch, A. L. Angew. Chem. Int. Ed. 2010, 49, 886-890; b) Chilingarov, N. S.; Troyanov, S. I. Chem. Asian J. 2016, 11, 1896-1899; c) Yang, H.; Jin, H.; Che, Y.; Hong, B.; Liu, Z.; Gharamaleki, J. A.; Olmstead, M. M.; Balch, A. L. Chem. Eur. J. 2012, 18, 2792-2796; d) Fritz, M. A.; Kemnitz, E.; Troyanov, S. I. Chem. Commun. 2014, 50, 14577-14580. (14) Dennis, T. J. S.; Kai, T.; Asato, K.; Tomiyama, T.; Shinohara, H.; Yoshida, T.; Kobayashi, Y.; Ishiwatari, H.; Miyake, Y.; Kikuchi, K.; Achiba, Y. J. Phys. Chem. A 1999, 103, 8747-8752.
In summary, high-temperature chlorination of a mixture containing C88 fullerene resulted in the isolation and structural characterization of non-IPR, non-classical C84(NC2)Cl30. The C84(NC2) carbon cage contains two heptagons, two pairs of fused pentagons and two groups of quaternary sequentially fused pentagons, which are observed in carbon cages for the first time. All 30 Cl atoms are arranged in a remarkable single chain of adjacent additions. Topological reconstruction of the skeletal transformation revealed that the starting, previously unknown isomer C2-C88(3) undergoes two C2 losses and two Stone-Wales rearrangements thus resulting in a fullerene chloride with a high relative stability. In comparison with the non-IPR C76Cl24 (in which 10 of 12 pentagons are fused in pairs) achieved by the sevenstep cage transformation,3a the non-classical cage in 1 with 12 of 14 pentagons fused in pairs or quartets was obtained via only four transformation steps. This is obviously owing to the specific distribution of pentagons on the carbon cage of C88(3). The same reason seems to be responsible for preventing transformation of C88(3) into more stable IPR isomers of C88 during fullerene mixture annealing in the course of arc-discharged fullerene synthesis, thus explaining the presence of rather unstable C88(3) in the fullerene soot.
ASSOCIATED CONTENT Supporting Information. Isolation and MS characterization of a C92/C88-containing fraction, Detailed reconstruction of transformation pathways. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION Corresponding Author *
[email protected] (S. Y.);
[email protected] (E. K.);
[email protected] (S. I. T.).
Notes The authors declare no competing financial interest.
ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (nos. 21371164, 51572254, and 2151101074), the Deutsche Forschungsgemeinschaft (Ke489/39-2), and the Russian Foundation for Basic Research (grants 15-03-04464 and 16-53-53012).
REFERENCES (1) a) Hirsch, A.; Brettreich, M. Fullerenes: Chemistry and Reactions, Wiley-VCH, Weinheim, 2005; b) Goryunkov, A. A.; Markov, V. Yu.; Ioffe, I. N.; Bolskar, R. D.; Diener, M. D.; Kuvychko, I. V.; Strauss, S. H.; Boltalina, O. V. Angew. Chem. Int. Ed. 2004, 43, 997-1000; c) Wang, S.; Yang, S.; Kemnitz, E.; Troyanov, S. I. Inorg. Chem, 2016, 55, 5741-5743.
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