10384 19120051301858 UDC The Structures and Electronic Properties of Endohedral Metallofullerenes: A Theoretical Investigation 2008 6
1 2 2008 6 25 2008 6 25
(Endohedral Metallofullerenes) Sc 2 C 70 Sc 2 C 70 Sc 2 @C 70 Sc 2 C 2 @C 68 (Sc 3+ ) 2 (C 2 ) 2 @C 68 4 M 2 C 2 @C 78 (M=Ti, Zr, Hf) M 2 C 80 (M=Ti, Zr, Hf) M 2 @C 80 M 2 C 2 @C 78 (M 4+ ) 2 (C 2 ) 2 @C 78 6 U 2 @C 60 U 2 @C 60 U 2 @C 60 (D 3d, 7 A 2u ) U 2 U-U U-U (5f u ) 2 (5f g ) 1 (5f g ) 2 (5f u ) 1 Sc 2 C 2n (30 n 43) i) Sc 2 C 2 @C 2n-2 Sc 2 @C 2n (Sc 3 ) 2 (C 2 ) 2 @C 4 2n-2 (Sc 3 ) 2 @C 6 2n ii) Sc 2 C 2n (2n = 60, 62, 64, 68) iii) Sc 2 C 70 Sc 2 C 2 @C 68 Sc 2 C 2n (2n = 66, 72 82) Sc 2 @C 2n Sc 2 C 2n (2n 84) Sc 2 C 2 @C 2n-2 I
Abstract Abstract Endohedral metallofullerenes (EMFs) are fullerene-based derivatives that have a metal atom or metal-containing cluster inside hollow fullerene cages. Due to their unique electronic structures, EMFs have attracted wide interests in the past two decades. However, structural determinations of EMFs are still quite a challenge because of low yields in Krätschmer-Huffman arc-discharge reactions, difficulties in separations and purifications, complicated and low signal-to-noise 13 C NMR spectra and lacks of suitable single crystals for X-ray diffraction analyses et al. It s an essential issue of determining the structures of EMFs in order to understand their optical, magnetic and chemical properties for the potential applications. Based on the fullerene topology, we carried out systematic investigations on structures and electronic properties of EMFs by means of quantum chemical computations. The results are summarized as follows: 1. Sc 2 C 70 : Sc 2 C 70 takes the form of Sc 2 C 2 @C 68, but not Sc 2 @C 70. Its formal charge state can be described as (Sc 3+ ) 2 (C 2 ) 2 @C 68 4. 2. M 2 C 2 @C 78 (M=Ti, Zr, Hf): Structures of the M 2 C 80 (M=Ti, Zr, Hf) series are M 2 C 2 @C 78 instead of previous assigned M 2 @C 80. The formal charge states of these dimetallic carbide endofullerenes are (M 4+ ) 2 (C 2 ) 2 @C 78 6. 3. U 2 @C 60 : The ground state of U 2 @C 60 is U 2 @C 60 (D 3d, 7 A 2u ). The encapsulated U 2 cluster has a sixfold ferromagnetically coupled one-electron-twocenter U-U bond with the electronic configuration of (5f u ) 2 (5f g ) 1 (5f g ) 2 (5f u ) 1. 4. Structural rules of Sc 2 C 2n (30 n 43): i) formal charge states for the most stable Sc 2 C 2 @C 2n-2 and Sc 2 @C 2n are (Sc 3 ) 2 (C 2 ) 2 @C 4 2n-2 and (Sc 3 ) 2 @C 6 2n, respectively; ii) Sc 2 C 2n with small fullerenes (2n = 60, 62, 64, 68) are unstable in experiments; iii) except for Sc 2 C 70, Sc 2 C 2n with medium (2n = 66, 72 82) and large (2n 84) cages prefer Sc 2 @C 2n and Sc 2 C 2 @C 2n-2 structures, respectively. Keywords: endohedral metallofullerene fullerene structure quantum chemical computation II
... I Abstract...II...1 1.1 1 1.1.1 2 1.1.2 5 1.2 7 1.2.1 7 1.2.2 9 1.2.3 10 1.2.4 11 1.2.5 14 1.3 15 1.4 16 17 Sc 2 C 70...21 2.1 21 2.2 21 2.3 21 2.4 27 28 M 2 C 2 @C 78 M = Ti, Zr, Hf...31 3.1 31 3.2 31 3.3 32 3.3.1 Ti 2 C 2 @C 78 32 3.3.2 Hf 2 C 2 @C 78 33 3.3.3 Zr 2 C 2 @C 78 34 I
3.4 36 38 U 2 @C 60...40 4.1 40 4.2 40 4.3 41 4.3.1 U 2 @C 60 (I h ) 41 4.3.2 U 2 @C 60 (I h ) U-U 44 4.3.3 IPR C 60 U 2 @C 60 48 4.4 49 51 Sc 2 C 2n (30 n 43)...56 5.1 56 5.2 58 5.3 58 5.3.1 C q 2n (q = 4, 6; 30 n 35) 58 5.3.2 Sc 2 C 2n (n = 60, 66, 70) 61 5.3.3 Sc 2 C 2n (36 n 39) 67 5.3.4 Sc 2 C 2n 81 5.4 85 86...93...94 II
1.1 [1] 10 9 m C 60 (I h ) 0.4Å [1] [2] 1. 1 LaC n C n 1
1.1.1 Kroto 1985 C 60 (I h ) [1] LaCl 2 LaC n ( 1. 1) LaC 60 LaC 60 La C 60 (I h ) LaC 60 H 2 O 2 NO NH 3 LaC 60 C 60 La ( La@C 60 ) [3] 1990 Krätschmer C 60 [4] [2] La@C 60 La@C 82 [5] La@C 60 La@C 60 1992 Johnson (ESR) La@C 82 [6] ESR La@C 82 3 C 82 +3 La@C 82 La 3 @C 82 3 La@C 82 [7] ESR La 3 @C 82 3 [8] 1995 Y@C 82 X C 82 [9] Y@C 82 Y 3 @C 3 82 C 82 3 La 2 @C [10] 80 Sc 3 N@C [11] 68 Sc 2 C 2 @C [12] 82 Sc 3 N@C [13] 80 Sc 3 C 2 @C [14] 80 Tb 3 N@C [15] 84 ( 1. 2) 100 [16] ( ) 2
2 3 4 [17] 13 C NMR 13 C [18] X 1. 2 a) La 2 @C 80 b) Sc 3 N@C 68 c) Sc 2 C 2 @C 82 d) Sc 3 N@C 80 e) Sc 3 C 2 @C 80 f) Tb 3 N@C 84 3
1. 3 a) C 80 (I h ) b) C 80 6 (I h ) SOMO (Singly Occupied Molecular Orbital) HOMO (Highest Occupied Molecular Orbital) LUMO (Lowest Unoccupied Molecular Orbital) [19] [20] [21] 129 La 13 C La 2 @C 80 5 kcal/mol [22] ( ) (Isolated Pentagon Rule IPR) [23] IPR C 60 (I h ) 8- Sc 3 N@C 68 Sc 3 N C 68 ( 1. 2) Sc 3 N@C 68 IPR C 68 IPR HOMO-LUMO C 80 (I h ) [24] 1. 3a C 80 (I h ) 4
1. 4 Sc 2 C 66 a) Shinohara Sc 2 C 66 Sc 2 @C 66 (# 4348) b) Nagase Sc 2 C 66 Sc 2 @C 66 (# 4059) Sc C 80 (I h ) C 80 6 (I h ) ( 1. 3b) M 3 N@C 80 (I h ) (M = Sc, Gd, Lu) [25] (M 3 ) 3 N 3 @C 80 6 C 80 6 (I h ) 1.1.2 13 C 1. 4a Shinohara [10] 13 C X Sc 2 C 66 Sc 2 @C 66 (# 4348) [26] (Sc 2 ) 2 2 @C 66 [27] Nagase Sc 2 C 66 Sc 2 @C 66 (# 4059) (Sc 3 6 ) 2 @C [28] 66 Sc 2 @C 66 (# 4348) Sc 2 @C 66 (# 4059) Sc 2 Sc 2 @C 66 (# 4348) Sc-Sc 5
1. 5 Ti 2 C 80 a) Yumura Ti 2 C 80 Ti 2 C 2 @C 78 b) c) Shinohara Ti 2 C 80 Ti 2 @C 80 (D 5h ) Ti 2 @C 80 (I h ) Ti 2 C 2 @C 78 2.87 Å Sc 2 @C 66 (# 4059) Sc-Sc 4.93 Å Sc- Sc Sc 2 @C 66 (# 4348) Sc 2 Sc 2 @C 66 (# 4059) Sc 2001 Shinohara (Electron Energy Loss Spectroscopy, EELS) 13 C Ti 2 C 80 Ti 2 @C 80 (D 5h ) Ti 2 @C 80 (I h ) ( 1.5 b c) [29] [30] Yumura [31] (High Resolution Transmission Electron Microscopy, HR-TEM) Ti 2 C 80 Ti 2 C 2 @C 78 1. 6 Sc 2 C 84 (III) a) Akasaka Sc 2 C 84 (III) Sc 2 C 2 @C 82 b) Shinohara Sc 2 C 84 (III) Sc 2 @C 84 Sc 2 C 2 @C 82 6
( 1. 5a) (Ti 4 ) 2 (C 2 ) 2 @C 6 78 1996 Shinohara Sc 2 C 84 (III) [32] 13 C NMR (10 1 ) Sc 2 C 84 (III) Sc 2 @C 84 (Sc 3 ) 2 @C 6 84 ( 1. 6b) [33] X [34] Sc 2 C 84 (III) 2006 Akasaka Sc 2 C 84 (III) 13 C NMR [35] 13 C NMR 17 13 C NMR 11 5 1 1/6 Akasaka Sc 2 C 84 (III) Sc 2 C 2 @C 82 ( 1. 6a) 2007 Sc 2 C 84 (III) 45 Sc 13 C Sc 2 C 84 (III) Sc 2 C 2 @C 82 (Sc 3 ) 2 C 2 2 @C 82 4 [36] Sc 2 C 2 @C 82 Sc 2 C 2 V Ti 2 C 2 @C 78 1.2 13 C [26] 1.2.1 (v) (e) (f) 7
Equation Section 1 v f e 2 (1.1) 1 sp 2 2 (v) (f) 5p 6h v 3 (1.2) v f p h 2 2 p h (1.2) p 12 v (1.3) h 10 2 (C n ) 12 n 10 2 Goldberg [37] 1. 7 8
1 20 C 22 22 2 e 3v 2 1.2.2 (v) (f) (e) 1. 7 1. 8 O h 1. 8 a b 9
1. 9 a) C 60 (I h ) b) C 60 (I h ) C 60 (I h ) I h delta- n 12 n 10 2 1.9 C 60 (I h ) delta- 1 2 1.2.3 Coxeter [38] [39] 1 10
200 C 200 2 100 100 Stone-Wales C 2 [40] 13 C 1.2.4 1 2 1. 10 C 20 (I h ) Schlegel 11
1. 10 C 20 (I h ) C 20 (I h ) 1. 1 connect(face_i,rim(face_i))=face_j i face_i rim(face_i) j face_j 1. 1 C 20 (I h ) / / 3 1 2/2 2 1/2 4 1 3/3 2 1/3 5 1 4/3 2 1/4 6 1 5/3 2 1/5 3 2/3 7 1 6/4 2 2/4 8 1 7/3 9 1 8/4 10 1 9/4 11 1 10/4 12 1 11/5 2 2/5 3 3/4 2 3/5 3 4/4 2 4/5 3 5/4 2 5/5 3 6/5 4 7/4 2 7/5 3 8/5 4 9/5 5 10/5 12
C 20 (I h ) ( 1. 10) 555555555555 spiral(12)= 55555555555 C n 12 n 10 2 n 2! 2 12! n 10! 2 C 60 225,792,840 55555555555656666666666666666666 1. 11 C 60 (I h ) Schlegel C 60 (I h ) 1.12 a) b) c) 56666656565656566565656565666665 (1.4) 65656566656656656566566565656566 (1.5) 66565656566566565665665666565656 (1.6) (1.4) (1.5) (1.6) spiral_1(32) 1. 11 C 60 (I h ) Schlegel 13
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