Stability and electronic spectra of C₇₆N₂ isomers

Stability and electronic spectra of C 76 N 2 isomers first-author †E-mail:wuteng@mail.hz.zj.cn †E-mail:wuteng@mail.hz.zj.cn wuteng@mail.hz.zj.cn Department of Chemistry, Zhejiang University, Hangzhou 310027, China Department of Chemistry, Zhejiang University, Hangzhou 310027, China Study of geometries of 16 possible isomers for C 76 N 2 based on C 78 ( C 2v ) by intermediate neglect of differential overlap (INDO) series of methods indicated that the most stable geometry 25,78-C 76 N 2 where two nitrogen atoms substitute two apexes C(25) and C(78) near the shortest X axis and Y axis formed by two hexagons and a pentagon. Electronic structures and spectra of C 76 N 2 were investigated. The reason for the red-shift for absorptions of C 76 N 2 compared with that of C 78 ( C 2v ) is discussed. C 76 N 2 Electronic spectra INDO INTRODUCTION 1 The synthesis and characterization of heterofullerenes are very challengeable research topics because of application in superconductivity, photoelectronics, organic magnetism and even nanotubes. Pradeep et al.( 1991 1991 ) studied the interaction between nitrogen and fullerenes and obtained nitrogen derivatives of C 60 and C 70 such as C 59 N 2 , C 59 N 4 , C 59 N 6 and C 70 N 2 by contact-arc vaporization of graphite in a partial N 2 or NH 3 atmosphere. Yu et al.( 1995 1995 ) synthesized carbon nanotubes and nitrogen-doped fullerenes by arcing a graphite rod in a pure nitrogen atmosphere and observed C 59 N − by mass spectra. Hummelen et al.( 1995 1995 ) isolated the heterofullerene C 59 N as its dimmer (C 59 N) 2 . Nuber and Hirsh ( 1996 1996 ) found a new way to synthesize nitrogen heterofullerenes RC 59 N and RC 69 N and achieved (C 69 N) 2 by heating butylamino adducts of diazafullerenes with toluene-p-sulfonic acid. Esfarjani et al.( 1994 1994 ) investigated the bonding and electronic properties of substituted fullerenes C 58 BN. Wang et al.( 1995 1995 ) theoretically analyzed C 60− x N x and C 60− x B x ( x =1~2) and their study on the stability of heterohedral fullerenes showed that the 6/6 site is favorable for C 58 N 2 while the 5/6 site is favorable for C 58 B 2 according to molecular mechanics calculations. Lamparth et al.( 1995 1995 ) used bisazafulleroid as a precursor to prepare bisadducts, which directly fragment to form the heterofullerene ions C 59 N + and C 69 N + –the isoelectronic heteroanalogues of C 60 and C 70 , and gave the resonance structures of C 59 N + using Austin model 1 (AM1) method. We used INDO series of methods to study stabilities of isomers and electronic spectra for C 75 N + (Wu and Teng, 2002 2002 ) and C 75 B − (Teng et al., 2003 2003 ), which showed that the substitution of other atoms leads to the decrease in symmetry and the red-shift of absorptions in electronic spectra. Benz et al.( 1996 1996 ) characterized C 78 ( C 2v ) with 21 unique carbon atoms and C 78 ( C 2v ′ ) with 22 unique carbon atoms by nuclear magnetic resonance (NMR), ultraviolet visible (UV), infra-red (IR) and Raman spectra, and indicated that the properties of higher fullerenes must be treated on an individual basis when they share the same number of atoms and symmetry. Based on C 78 ( C 2v ), here we study C 76 N 2 to predict electronic structures and stabilities of isomers and calculate electronic spectra. We also discuss electronic transition theoretically and the red-shift of absorption peaks of C 76 N 2 relative to that of C 78 ( C 2v ). CALCULATIONAL METHODS 1 We used standard bond lengths as an initial input for C 78 ( C 2v ) and implemented full geometry optimization with the INDO/2 method without any symmetry restriction and obtained C 78 ( C 2v ) (Fig. 1 1 ). Then we used a nitrogen atom to substitute 21 unique carbon atoms to get the most stable isomer where C(78) is substituted. After that we replaced other carbon atoms such as C(69), C(68) and so on using the second nitrogen atom to get 16 possible isomers. Full geometry optimization was carried out using the same method as described above to obtain equilibrium geometries. Electronic spectra were computed by intermediate neglect of differential overlap/configuration interaction for singlet (INDO/CIS) (Wu and Teng, 2002 2002 ; Teng et al., 2003 2003 ) as in the INDO program improved by Michael C. Zerner without any parameter adjustments. One-hundred ninety-seven configurations were generated by exciting electrons from the 14 highest occupied molecular orbitals (HOMO) into the 14 lowest unoccupied molecular orbitals (LUMO). RESULTS AND DISCUSSION 1 Stabilities of isomers 2 The relative energy and LUMO-HOMO energy gap of 16 isomers for C 76 N 2 are given in Table 1 1 showing that the most stable isomer is 25,78-C 76 N 2 where two nitrogen atoms locate at two apexes of two hexagons and a pentagon near the shortest X axis and Y axis of C 78 ( C 2v ) because the apexes are connected with relatively weak 6/5 bonds. Lengths of C-N bonds were 0.1312, 0.1317 and 0.1325 nm and bond orders were 1.0844, 1.0678 and 1.0496, forming C-N single bonds. The second stable isomer is 49,78-C 76 N 2 , N(49), which also substitutes near the X axis, and more stable than 28,78-C 76 N 2 by 0.1949 eV; N(28) locates near the longest Z axis of C 78 ( C 2v ). The next four stable isomers are those where two nitrogen atoms are separated from each other. From 71,78-C 76 N 2 and 73,78-C 76 N 2 we can see that 1,4-substitution is more stable than 1,2-substitution on the hexagon. It is noted that the unstable isomers are those where two nitrogen atoms are connected with each other, which leads to higher energies from 29,30-C 76 N 2 to 1,10-C 76 N 2 . Bond lengths and orders for C-N bonds in other isomers are 0.1281~0.1348 nm and 1.0138~1.1879. Isomers Energy L-H gap 25,78-C 76 N 2 0 3.4578 49,78-C 76 N 2 0.1910 3.5315 28,78-C 76 N 2 0.1949 3.4883 24,78-C 76 N 2 0.2201 3.4749 6,78-C 76 N 2 0.4185 3.4804 7,78-C 76 N 2 0.5220 3.4461 48,78-C 76 N 2 0.6620 3.5040 71,78-C 76 N 2 0.6708 3.4325 68,78-C 76 N 2 0.7798 3.3710 29,30-C 76 N 2 2.4413 3.5174 70,71-C 76 N 2 3.0077 3.5430 69,78-C 76 N 2 3.3090 3.1795 73,78-C 76 N 2 3.5660 3.5516 52,53-C 76 N 2 4.0588 3.4670 47,48-C 76 N 2 4.1177 3.6110 1,10-C 76 N 2 4.8244 3.3802 Electronic structures 2 25,78-C 76 N 2 is a stable closed-shell molecule where LUMO-HOMO energy gap is 3.4578 eV. Other isomers in Table 1 1 possess much less LUMO-HOMO energy gap than that of C 78 ( C 2v ) (4.7534 eV). Molecular orbitals for C 76 N 2 isomers are non-degenerate owing to the lower symmetry. In 25,78-C 76 N 2 , two nitrogen atoms carry positive Mülliken charges 1.589 and 1.590 whereas the adjacent carbon atoms are of negative charges from −0.467 to −0.557, leading to the formation of polar covalent bonds. At the same time, the positive charge is chiefly concentrated on two nitrogen atoms, which makes them become further reaction centers for nuclearphilic reagents. For the rest of the isomers, Mülliken charges of nitrogen atoms and successive carbon atoms are within the regions of 1.171~1.602 and −0.443~0.620. Electronic spectroscopy 2 The INDO/CIS method can be used successfully for computing electronic spectra of carbon clusters (Wu and Teng, 2002 2002 ; Teng et al., 2003 2003 ). UV bands of C 78 ( C 2v ) are at 289.9, 310.2, 328.8, 370.7, 434.4, 466.7, 527.6 and 614.0 nm, and are consistent with the experiment values of 290, 310, 330, 370, 430, 470, 530 and 590 nm (Benz et al., 1996 1996 ). The first absorption of 25,78-C 76 N 2 is at 1484.6 nm (Table 2 2 ), generated by electronic transition from HOMO (157) to LUMO (158). Strong absorption appearing at 913.2 nm, resulted from electronic excitation from (157) to (161). The first peak of 49,78-C 76 N 2 locates at 1456.6 nm, generated by electronic transition from (157) to (158). The absorptions for 25,78-C 76 N 2 and 49,78-C 76 N 2 are red-shifted relative to that of C 78 ( C 2v ) due to less LUMO-HOMO energy gaps. Isomers λ (nm) Oscill. Trans. nature coeffic. 25,78-C 76 N 2 1484.6 0.0297 (157)→(158) 0.7700 25,78-C 76 N 2 1209.7 0.0033 (157)→(159) 0.7527 25,78-C 76 N 2 985.2 0.0381 (157)→(160) 0.8554 25,78-C 76 N 2 913.2 0.1334 (157)→(161) −0.7561 25,78-C 76 N 2 807.6 0.0279 (157)→(162) −0.8754 25,78-C 76 N 2 692.3 0.0032 (157)→(163) 0.6966 49,78-C 76 N 2 1456.6 0.0205 (157)→(158) 0.7914 49,78-C 76 N 2 1183.6 0.0135 (157)→(159) 0.7251 49,78-C 76 N 2 952.2 0.0339 (157)→(160) −0.8013 49,78-C 76 N 2 891.4 0.1236 (157)→(161) −0.8059 49,78-C 76 N 2 787.9 0.0195 (157)→(162) 0.8972 49,78-C 76 N 2 630.0 0.0609 (156)→(158) 0.8019 The first peak of 28,78-C 76 N 2 is at 1387.7 nm (Table 3 3 ), generated by electronic transition from (157) to (159). The strong band is at 928.4 nm, owing to electronic transition from (157) to (161). The first band of 24,78-C 76 N 2 is at 1559.2 nm, generated by electronic transition from (157) to (158). The near infra-red (NIR) absorptions for 25,78-C 76 N 2 and 24,78-C 76 N 2 are caused by decrease in LUMO-HOMO energy gaps. Isomers λ (nm) Oscill. Trans. nature coeffic. 28,78-C 76 N 2 1387.7 0.0329 (157)→(159) 0.9023 28,78-C 76 N 2 1325.4 0.0263 (157)→(158) −0.9534 28,78-C 76 N 2 990.7 0.0280 (157)→(160) 0.8837 28,78-C 76 N 2 928.4 0.1211 (157)→(161) 0.8932 28,78-C 76 N 2 762.2 0.0243 (157)→(162) −0.9014 28,78-C 76 N 2 700.5 0.0057 (157)→(163) −0.6439 24,78-C 76 N 2 1559.2 0.0226 (157)→(158) 0.9109 24,78-C 76 N 2 1187.0 0.0233 (157)→(159) 0.8704 24,78-C 76 N 2 990.3 0.0254 (157)→(160) −0.9220 24,78-C 76 N 2 930.4 0.1057 (157)→(161) −0.8769 24,78-C 76 N 2 793.6 0.0431 (157)→(162) 0.8832 24,78-C 76 N 2 701.9 0.0107 (157)→(163) 0.7287 First peaks of electronic spectra for 6,78-C 76 N 2 and 7,78-C 76 N 2 (Fig. 2 2 ) appearing at 1534.4 and 1518.0 nm are produced by electronic transitions from (157) to (158) and (157) to (159). The red-shift of the first peaks for 6,78-C 76 N 2 and 7,78-C 76 N 2 compared with that of C 78 ( C 2v ) happens owing to less LUMO-HOMO energy gaps. Table 4 4 indicates that first peaks of electronic spectra for other C 76 N 2 isomers are red-shifted relative to that of C 78 ( C 2v ), which is attributable to less LUMO-HOMO energy gaps. These NIR peaks are characteristics for recognizing different isomers in the experiment. Isomers λ (nm) Oscill. 48,78-C 76 N 2 1474.4 0.0196 48,78-C 76 N 2 1250.8 0.0220 48,78-C 76 N 2 972.3 0.0346 71,78-C 76 N 2 1587.7 0.0191 71,78-C 76 N 2 1297.7 0.0160 71,78-C 76 N 2 1023.9 0.0221 68,78-C 76 N 2 1711.7 0.0174 68,78-C 76 N 2 1449.9 0.0158 68,78-C 76 N 2 1039.3 0.0384 29,30-C 76 N 2 1306.9 0.0028 29,30-C 76 N 2 1042.9 0.0123 29,30-C 76 N 2 1032.1 0.0258 70,71-C 76 N 2 1463.6 0.0178 70,71-C 76 N 2 1061.1 0.0031 70,71-C 76 N 2 957.7 0.0107 69,78-C 76 N 2 2399.5 0.0122 69,78-C 76 N 2 1593.6 0.0033 69,78-C 76 N 2 1251.2 0.0658 73,78-C 76 N 2 1344.1 0.0103 73,78-C 76 N 2 989.6 0.0017 73,78-C 76 N 2 861.6 0.2220 52,53-C 76 N 2 1647.5 0.0289 52,53-C 76 N 2 1054.8 0.0229 52,53-C 76 N 2 927.6 0.0427 47,48-C 76 N 2 1280.3 0.0293 47,48-C 76 N 2 935.0 0.0320 47,48-C 76 N 2 894.0 0.1232 1,10-C 76 N 2 1470.3 0.0120 1,10-C 76 N 2 1253.0 0.0266 1,10-C 76 N 2 1126.3 0.0012 CONCLUSION 1 ZINDO methods can be successfully used for optimizing geometries and electronic spectra of C 76 N 2 isomers. The most stable isomer is 25,78-C 76 N 2 where two nitrogen atoms are separated and located near two shorter axes. The red-shift of absorptions in electronic spectra for C 76 N 2 compared with that of C 78 ( C 2v ) takes place because of less LUMO-HOMO energy gap for C 76 N 2 . References M Benz , M Fanti , PW Fowler , D Fuchs , MM Kappes , C Lehner , RH Michel , G Orlandi , F Zerbetto . Experimental and theoretical study of the infrared, Raman, and electronic spectra of two isomers of C 78 of C 2v symmetry . J Phys Chem , 1996 . 100 ( 32 ): 13399 - 13407 . . Experimental and theoretical study of the infrared, Raman, and electronic spectra of two isomers of C78 of C2v symmetry K Esfarjani , K Ohmo , Y Kawazoe . Band structure and electronic bonding in C 58 BN heterofullerenes . Phys Rev B Condns Matter , 1994 . 50 17830 - 17836 . . Band structure and electronic bonding in C58BN heterofullerenes JC Hummelen , B Knight , J Pavlovich , R González , F Wudl . Isolation of the heterofullerene C 59 N as its dimmer (C 59 N) 2 . Science , 1995 . 269 1554 - 1556 . . Isolation of the heterofullerene C59N as its dimmer (C59N)2 I Lamparth , B Nuber , G Schick , A Skiebe , T GrÖsser , A Hirsch . C 59 N + and C 69 N + : Isoelectronic heteroanalogues of C 60 and C 70 . Angew Chem Int Ed Engl , 1995 . 34 ( 20 ): 2257 - 2259 . . C59N+ and C69N+: Isoelectronic heteroanalogues of C60 and C70 B Nuber , A Hirsh . A new route to nitrogen heterofullerenes and the first synthesis of (C 69 N) 2 . Chem Commun , 1996 . 1421 - 1442 . . A new route to nitrogen heterofullerenes and the first synthesis of (C69N)2 T Pradeep , V Vijayakrishnan , AK Santra , CNR Rao . Interaction of nitrogen with fullerenes: Nitrogen derivatives of C 60 and C 70 . J Phys Chem , 1991 . 95 10564 - 10568 . . Interaction of nitrogen with fullerenes: Nitrogen derivatives of C60 and C70 QW Teng , S Wu , ZY Zhu . Theoretical studies on the structures and electronic spectra of C 75 B − . Int J Quantum Chem , 2003 . 91 39 - 45 . . Theoretical studies on the structures and electronic spectra of C75B− SH Wang , F Chen , YC Fann , M Kashani , M Malaty , SA Jansen . Assessment of the stability of heterohedral fullerenes: A theoretical analysis of C 60− x N x and C 60− x B x , where x =1 and 2 . J Phys Chem , 1995 . 99 6801 - 6807 . . Assessment of the stability of heterohedral fullerenes: A theoretical analysis of C60−xNx and C60−xBx, where x=1 and 2 S Wu , QW Teng . Studies on electronic structures and spectra of C 75 N + . Chem J Chinese Universities , 2002 . 23 ( 1 ): 132 - 134 . (in Chinese) . Studies on electronic structures and spectra of C75N+ R Yu , M Zhan , D Cheng , S Yang , Z Liu , L Zheng . Simultaneous synthesis of carbon nanotubes and nitrogen-doped fullerenes in nitrogen atmosphere . J Phys Chem , 1995 . 99 1818 - 1819 . . Simultaneous synthesis of carbon nanotubes and nitrogen-doped fullerenes in nitrogen atmosphere 10.1631/jzus.2005.B0602 2004-12-24 2005-03-20 2005-05-22 2022-01-05 Copyright © 2005, Journal of Zhejiang University Science 2005 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 06 6B