C64H6的结构和光谱的理论研究

本文用INDO系列方法研究了C64H6的结构与光谱, 表明C64H6有C2v和Cs两种稳定构型, 其中C2v构型能量较低, 讨论其加成及环加成产物对称性的规律并与13C NMR谱的实验结果相结合。计算了两种构型的电子光谱, 对电子跃迁进行了理论指认,并讨论了C64H6谱带红移的原因, 理论计算结果与实验事实基本吻合。     

C_(70)O的结构和UV-Vis光谱的理论研究

用INDO系列方法对C_70O的8种异构体构型进行系统研究,表明C_70O中O主要加在C_1一C_2和C_3—C_3键上,形成具有C_S对称性且不开环的环氧化合物结构.以优化构型为基础,进行UV-Vis光谱计算,表明C_70O主峰与C_70基本一致,并在460um以上产生特征吸收峰,计算结果与实验值一致.在对其特征吸收峰进行理论指认的同时,讨论了吸收峰红移的原因,并指出C_70O可能由4种异构体组成.     

几种C_(60)环加成物的结构及光谱的理论研究

用INDO系列方法研究了C60的几种环加成衍生物C68H8、C68H6O、C68H4O2的结构和UV谱．结果表明，C68H8的［6，6］异构体的船式构象比平面构象稍稳定，两者能量差为9．6kJ／mol；而随着衍生物中羰基的增加，C60母体也由电子受体变为电子给体．以优化构型为基础，计算产物的UV谱，对电子跃迁进行理论指认，并分析了光谱红移的原因．     

C70S可能异构体的结构与稳定性的理论研究

分别用半经验的AMl，PM3及MNDO方法研究了富勒烯衍生物C70S的12种可能异构体的结构和稳定性．计算结果表明：S原子加成在4种6-6键上的稳定构型中，非赤道带6-6键加成的三个异构体为闭环结构，赤道带6-6键加成的一个异构体为开环结构；S原子加成在4种6-5键上均可产生开环和闭环两种稳定构型．加成在6-5双键的异构体其闭环构型更稳定，加成在6-5单键的异构体其开环构型更稳定．闭环异构体中S原子加成在碳球极处6-6键上的构型1，2最稳定，开环异构体中S原子加成在赤道带6-6键上的构型8最稳定．     

N—乙基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用ＩＮＤＯ系列方法对Ｎ－乙基吩噻嗪及其自由基正离子进行了几何构型优化，得到中性分子为蝶状折叠形，自由基正离子为平面构型，以优化构型为基础计算其电荷密度，自旋密度键序和电子光谱。对光谱进行理论指认并讨论了从中性分子到离子谱带红移的原因，理论计算结果法与实验结果一致。     

C~6~0SiH~2的结构和电子光谱的量子化学研究

用INDO系列方法研究了C~6~0SiH~2的两种结构: 一是SiH~2加在两个六元环之间的键上形成C~2~v构型; 另一是SiH~2加在一个五元环和一个六元环之间的键上形成C~s构型。从总能量和LUMO-HOMO能级差看, C~6~0SiH~2的稳定结构应是C~2~v构型, 其中桥C(15)-C(30)的键长为0.1508nm, 键序为0.9369, 说明不开环, 形成类环丙烷结构。文中计算了两种构型的电子吸收光谱和NMR谱, 此类计算是基于对C~6~0SiH~2的等电子体C~6~0O和C~6~0CH~2的研究之上, 且后两者的研究结果与实验相一致。     

N－乙基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用ＩＮＤＯ系列方法对Ｎ－乙基吩噻嗪及其自由基正离子进行了几何构型优化，得到中性分子为蝶状折叠形，自由基正离子为平面构型。以优化构型为基础计算其电荷密度、自旋密度、键序和电子光谱。对光谱进行理论指认并讨论了从中性分子到离子谱带红移的原因。理论计算结果均与实验结果一致。     

DFT方法理论研究星际分子C3S+结构和光谱

在B3LYP／6—31lG(d)水平上对可能的星际分子C3S^ 的各种异构体进行了理论计算研究，得到其几何构型、红外光谱和精确能量以利于实验室和星际观测，讨论了其星际含义，并与其中性分子C3S做了比较．结果表明：C3S^ 有3个稳定的异构体，包括线形、三元环和四元环几何构型．按热力学稳定的异构体依次是直线型具有C∞v对称性的CCCS^ (1)，其次是具有CC桥键四元环构型的cC3S^ (2)，能量最高是三元环构型具有CC环外键的C—cCCS^ (3)。     

C_(70)PH可能异构体的结构与稳定性的理论研究

分别用半经验的AM1, PM3及MNDO方法研究了富勒烯衍生物C_(70)PH的12种可能异构体的结构和稳定性。计算结果表明: -PH基团加成在4种6-6键上的稳定构型中,非赤道带6-6键加成的三个异构体为闭环结构,赤道带6-6键加成的一个异构体为开环结构;-PH基团加成在4种6-5键上均可产生开环和闭环2种稳定构型。加成在6-5双键的异构体其闭环构型更稳定,加成在6-5单键的异构体其开环构型更稳定。闭环异构体中-PH基团加成在碳球极处6-6键上的构型1,2最稳定,开环异构体中-PH基团加成在赤道带6-6键上的构型8最稳定。     

吩噻嗪、N-甲基吩噻嗪及其自由基正离子的结构和电子光谱的理论研究

用INDO系列方法对吩噻嗪、N-甲基吩噻嗪及其自由基正离子进行了几何构型优化, 中性分子为蝶状折叠形, 自由基正离子为平面构型。以优化构型为基础,计算了上述四种分子、离子的电荷密度、自旋密度、键序和电子光谱, 对光谱进行理论指认的同时, 讨论了从中性分子到离子谱带红移的原因。所有理论计算值均与实验值一致。     

Theoretical studies on structures and UV-Vis spectra of C_(70)O

Systematic studies on eight isomers of C70O were performed by means of INDO methods It has been indicated that the O atom is mainly added to the C1-C2 or C3-C3 bond and an epoxide feature with C1 symmetry is formed.Based on the optimized geometries,the UV-Vis spectra were calculated.It has been found that the main peaks of C70O resemble those of C70 and the characteristic absorptions beyond 460 nm are produced,which is m agree ment with the experimental results.Theoretical assignments about the absorptions were carried out and the reason for the red-shift of the absorptions was discussed.C70O is probably composed of four isomers according to the calculated results.     

3He NMR as a sensitive probe of fullerene reactivity: [2 + 2] photocycloaddition of 3-methyl-2-cyclohexenone to C70

The [2 + 2] photoadditions of 3-methyl-2-cyclohexenone to C70 and 3He@C70 have been studied by a combination of HPLC chromatography and FAB-MS, as well as IR and 1H and 3He NMR spectroscopies. The total yield of the mixture of monoadducts was 55% (67% on the basis of the recovered C70). The use of 3He NMR was especially powerful in determining the regioselectivity of the photoaddition reaction of enone to C70. Results of the 3He NMR experiments conducted on the product mixture implicate the two [6,6] bonds closest to the poles of the fullerene (C1-C2 and C5-C6) in the photoaddition process. This reaction mode is analogous to that of most thermal addition reactions to C70. Separation and characterization of the product mixture shows that eight distinct monoadducts are formed in the photoaddition, namely, the four diastereomeric adducts to the C1-C2 and C5-C6 bonds of the C70 cage, each consisting of cis- and trans-fused isomers in a ratio of 2:3. The major mode of photoaddition, accounting for 65% of the product mixture, involves addition to the C1-C2 bond of the ovoid fullerene. Mechanistic implications of these findings are discussed.     

Study of Two Puzzled Questions on the Fullerene C_（70）：A First-principles Study

The cycloaddition reactions of NH to different bonds on C70 have been studied by the first-principles calculations.The results indicate that the reactivity of cycloaddition reactions is determined by the directional curvature,KD,and the larger binding energy of Eb on the bond C5-C'5 can be ascribed to the unique bond which can be treated as the shortest bond of(5.5)-SWCNT in the four [6,6] ring fusion bonds.This work also discloses that the energy gap of different spin states is decided by the electronic density,and that of the frontier obitals for the bond C5-C'5 is larger than the value for the C4-C'4 bond.Furthermore,the transition state investigation of the two bond addition reactions provides a reaction barrier of 11.10 kcal/mol for the NH cycloaddition to the C5-C'5 bond;whereas,the addition reaction on C4-C'4 is a spontaneous pathway.Herein,the dynamics effect illustrates the [2+1] cycloaddition reaction on the equatorial C5-C'5 bond to be unfavorable.     

Semiempirical molecular dynamics studies of C60/C70 fullerene oxides: C60O, C60O2 and C70O

The spectral analysis indicates that all isomers of C₆₀O, C₇₀O and C₆₀O₂ have an epoxide-like structure (an oxygen atom bridging across a C–C bond). According to the geometrical structure analysis, there are two isomers of fullerene monoxide C₆₀O (the 5,6 bond and the 6,6 bond), eight isomers of fullerene monoxide C₇₀O and eight isomers of fullerene dioxide C₆₀O₂. In order to simulate the real reaction conditions at 300 K, the calculation of the different isomers of C₆₀O, C₆₀O₂ and C₇₀O fullerene oxides was carried out using the semiempirical molecular dynamics method with two different approaches: (a) consideration of the geometries and thermodynamic stabilities, and (b) consideration of the ozonolysis mechanism. According to the semiempirical molecular dynamic calculation analysis, the probable product of this ozonolysis reaction is C₆₀O with oxygen bridging over the 6–6 bond (C_2v). The most probable product in this reaction contains oxygen bridging across in the upper part of C₇₀ (6–6 bond in C₇₀O-2 or C₇₀O-4) an epoxide-like structure. C₆₀O₂-1, C₆₀O₂-3 and C₆₀O₂-5 are the most probable products for the fullerene dioxides. All of these reaction products are consistent with the experimental results. It is confirmed that the calculation results with the semiempirical molecular dynamics method are close to the experimental work. The semiempirical molecular dynamics method can offer both the reaction temperature effect by molecular dynamics and electronic structure, dipole moment by quantum chemistry calculation.     

trans—和cis—(η~5—C_5Me_5)2Mo_2(μ_2—S)_2(t—O)_2[Me=CH_3—]的合成和结构

trans—(η~5—C_5Me_5)_2Mo_2(μ_2—S)_2(t—O)_2[Ⅰ]和cis—(η~5—C_5Me_5)Mo_2(μ_2—O)_2(t—O)_2(Ⅱ]是由Mo(CO)_6和C_5(CH_3)_5H的反应产物(η~5—C_5Me_5)_2Mo_2(CO)_4与(CH_2)_3S反应中同时得到的。晶体[Ⅰ]属四方晶系,空间群为P4_2/n,单胞参数;a=b=16.317,c=8.463,V=2253.16,Z=4。晶体[Ⅱ]亦属四方晶系,空间群为P42_1c,单胞参数:a=b=12.101,c=15.425,V=2258.54,Z=4 [Ⅰ]和[Ⅱ]分子分别具有C_1—T和C_2—2对称性。如把C_5Me_5-看成具有理想的园柱体对称性,则它们分别具有C_(2h)—2/m和C_(2v)—mm2对称性。在[Ⅰ]中Mo_2(μ_2—S)_2为菱形平面结构,而[Ⅱ]中则畸变成“蝶式”结构。由两个钼原子之间的距离(2.902和2.808)可以看出钼一钼间作用属于单键的范围内。所以它们是具有金属单键的双钼金属簇的两个立体异构体。     

An efficient approach for theoretical study on the low-energy isomers of large fullerenes C90-C140

An approach that consists of a molecular mechanics method based on the second generation reactive empirical bond order (REBO) potential and the more accurate semiempirical method PM3 (Parametric Method No. 3) was proposed to predict the energetically favored isomers of the fullerenes from C90 to C140 at the semiempirical level. All the 578,701 isolated-pentagon-rule isomers of fullerenes from C90 to C140 were enumerated from topological structures and systematically searched using an energy minimization method to select the best 100 low-energy isomers based on the REBO potential for each fullerene. Then these candidate isomers were further optimized by PM3 and ranked again to determine the top low-energy isomers. This approach was applied to calculate the energetically favored isomers of C90-C140. The results of C90-C120 are in good agreement with the published results by quantum-chemical methods. Furthermore, the top five low-energy isomers of C90-C120, as well as C122-C140 which have scarcely been systematically studied before, are also predicted with the approach. The analysis of the structures showed that the hexagon-neighbor rule is an important factor to the stability of C90-C140. The time cost for the systematical search based on the REBO potential was also discussed. It indicates that the approach proposed is efficient for predicting the energetically favored isomers of large fullerenes at the semiempirical level.     

Preparation and NMR characterization of C70H10: cutting a fullerene pi-system in half

Three isomers of C70H10 were prepared by Zn(Cu) reduction of C70. Three chromatographic bands were identified as C70H10 species by MALDI-FT mass spectrometry, and these compounds were isolated by repeated HPLC treatments. The major isomer (2) was characterized by 1H and 13C NMR, while the minor isomers 3-4 were isolated in such small quantities that only 1H NMR analysis was possible. 1H-coupled and 1H-decoupled 13C NMR of 2 established a 7,8,19,26,33,37,45,49,53,63-substitution pattern. This assignment was confirmed by HMBC and DFQ-COSY experiments. This structure is completely reasonable, as we found that 2 results exclusively from reduction of the 7,19,23,27,33,37,44,53-C70H8 that is formed in the course of the Zn(Cu) reduction of C70.     

Synthesis, characterization, and theoretical study of stable isomers of C70(CF3)n (n = 2, 4, 6, 8, 10)

Reaction of C70 with ten equivalents of silver(I) trifluoroacetate at 320-340 degrees C followed by fractional sublimation at 420-540 degrees C and HPLC processing led to the isolation of a single abundant isomer of C70(CF3)n for n = 2, 4, 6, and 10, and two abundant isomers of C70(CF3)8. These six compounds were characterized by using matrix-assisted laser desorption ionization (MALDI) mass spectrometry, 2D-COSY and/or 1D 19F NMR spectroscopy, and quantum-chemical calculations at the density functional theory (DFT) level. Some were also characterized by Raman spectroscopy. The addition patterns for the isolated compounds were unambiguously found to be C1-7,24-C70(CF3)2, C1-7,24,44,47-C70(CF3)4, C2-1,4,11,19,31,41-C70(CF3)6, Cs-1,4,11,19,31,41,51,64-C70(CF3)8, C2-1,4,11,19,31,41,51,60-C70(CF3)8, and C1-1,4,10,19,25,41,49,60,66,69-C70(CF3)10 (IUPAC numbering). Except for the last compound, which is identical to the recently reported, crystallographically characterized C70(CF3)10 derivative prepared by a different synthetic route, these compounds have not previously been shown to have the indicated addition patterns. The largest relative yield under an optimized set of reaction conditions was for the Cs isomer of C70(CF3)8 (ca. 30 mol % of the sublimed mixture of products based on HPLC integration). The results demonstrate that thermally stable C70(CF3)n isomers tend to have their CF3 groups arranged on isolated para-C6(CF3)2 hexagons and/or on a ribbon of edge-sharing meta- and/or para-C6(CF3)2 hexagons. For Cs- and C2-C70(CF3)8 and for C2-C70(CF3)6, the ribbons straddle the C70 equatorial belt; for C1-C70(CF3)4, the para-meta-para ribbon includes three polar hexagons; for C1-7,24-C70(CF3)2, the para-C6(CF3)2 hexagon includes one of the carbon atoms on a C70 polar pentagon. The 10.3-16.2 Hz 7JF,F NMR coupling constants for the end-of-ribbon CF3 groups, which are always para to their nearest-neighbor CF3 group, are consistent with through-space Fermi-contact interactions between the fluorine atoms of proximate, rapidly rotating CF3 groups.     

富勒烯衍生物C50X(X=SiH2,PH,S)的结构及稳定性的理论研究

用从头算HF/3-21G方法研究了C50的环加成衍生物C50X(X=SiH2, PH, S)所有可能的异构体的结构与稳定性, 计算结果表明, SiH2基团、PH基团与S原子在C50上环加成的优先加成位置相同, 都为C3—C4类键和C4—C4类键, 并且相应形成[5,6]-闭环和[5,5]-闭环结构的最稳定异构体; 决定C50X(X=SiH2, PH, S)各异构体稳定性的主要因素, 因加成位置以及发生加成反应的C—C键的单双键类型的不同, 可能是张力、共轭效应或者二者的共同作用. 进一步比较了C50X(X=SiH2, PH, S)与C50X(X=CH2, NH, O)的结构和稳定性等, 并总结出规律性的结论, 即加成原子的大小和加成位置C—C键的类型是影响形成开环或闭环结构的C50环加成衍生物的两种主要因素.     

Asymmetry in platinum acetylide complexes: confinement of the triplet exciton to the lowest energy ligand

To determine structure-optical property relationships in asymmetric platinum acetylide complexes, we synthesized the compounds trans-Pt(PBu3)2(C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE1-2), trans-Pt(PBu3)2(C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE1-3) and trans-Pt(PBu3)2(C[triple bond]C-C6H4-C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE2-3) that have different ligands on either side of the platinum and compared their spectroscopic properties to the symmetrical compounds PE1, PE2 and PE3. We measured ground state absorption, fluorescence, phosphorescence and triplet state absorption spectra and performed density functional theory (DFT) calculations of frontier orbitals, lowest lying singlet states, triplet state geometries and energies. The absorption and emission spectra give evidence the singlet exciton is delocalized across the central platinum atom. The phosphorescence from the asymmetric complexes comes from the largest ligand. Time-dependent (TD) DFT calculations show the S1 state has mostly highest occupied molecular orbital (HOMO) --> lowest unoccupied molecular orbital (LUMO) character, with the LUMO delocalized over the chromophore. In the asymmetric chromophores, the LUMO resides on the larger ligand, suggesting the S1 state has interligand charge transfer character. The triplet state geometries obtained from the DFT calculations show distortion on the lowest energy ligand, whereas the other ligand has the ground state geometry. The calculated trend in the triplet state energies agrees very well with the experimental trend. Calculations of triplet state spin density also show the triplet exciton is confined to one ligand. In the asymmetric complexes the spin density is confined to the largest ligand. The results show Kasha's rule applies to these complexes, where the triplet exciton moves to the lowest energy ligand.