Searching for stable hept-C62X2 (X = F, Cl, and Br): structures and stabilities of heptagon-containing C62 halogenated derivatives

To determine the geometries of the most stable hept-C(62)X(2) (X = F, Cl, and Br) isomers, all 967 possible hept-C(62)F(2) isomers have been orderly optimized using AM1, HF/STO-3G, B3LYP/3-21G, and B3LYP/6-31G* methods, and chlorofullerenes and bromofullerenes, which are isostructural with five most stable hept-C(62)F(2) isomers, were regarded as candidates of the most stable isomer, and optimized at the B3LYP/6-31G* level. The results reveal that 2,9- and 9,62-hept-C(62)X(2) (X = F, Cl, and Br) are the two most stable isomers with slight energy difference. The halogenation releases strain energy of hept-C(62), and all halogenated fullerenes are more chemically stable than hept-C(62) with lower E(HOMO) and higher E(LUMO). All five most stable hept-C(62)X(2) (X = F, Cl, and Br) isomers are energetically favorable, and their thermodynamic stability decreases along with the increase of sizes of addends. Only hept-C(62)F(2) isomers show high thermodynamic stability, and they are potentially synthesized in experiments. 59,62-squ-C(62)X(2) (X = F, Cl, and Br) were computed for comparison, and they are found to be more stable than their heptagon-containing isomers.     

C36X(X=O,NH,S)各种可能异构体的芳香性研究

采用拓扑共振能方法对富勒烯C36X(X=O,NH,S)开环结构中的所有可能的异构体及阳离子和阴离子芳香性进行了理论研究. 计算结果表明,C36X的芳香性高于C36. C36X的阳离子因其共振能为负值而具有反芳香性. 反之,C36X的阴离子因共振能为正值而具有芳香性和较高的稳定性. C36的D6h和D2d异构体中杂原子X插入在5-5键时得到的化合物最稳定. 从理论上预测了C36X的负离子能形成稳定的金属富勒烯. 对C36X的阳离子和阴离子的芳香性进行了解释.     

C_(80)X_(12)(X=H,F,Cl,Br)的结构和稳定性

为了考察勒烯衍生物结构与稳定性关系,采用密度泛函理论方法对C80X12(X=H,F,Cl,Br)进行了系统计算究.结表明,在C80X12(X=H,F)异构体中,最低能量异构体都违反五元环分离规则.然而,在C80X12(X=Cl,Br)异构体中,最低能量异构体都满足五元环分离规则.由于van der Waals半径较小,H或F加成到碳笼上时外部原子之间排斥作用小,因此在其优结构中,H或F优先加成到2个五元环共用碳原子上.相反,对于氯化、溴化勒烯,为了避免外部加成原子之间在重空间排斥作用,其优结构中Cl或Br优先加成到1,4-位点上.计算结还显,氢化、卤化反应热(C80+6X2→C80X12)遵循如下顺序,即C80F12>C80Cl12>C80H12>C80Br12.这些结表明勒烯衍生物稳定性和衍生化模与加成原子尺和电性有关.     

Modeling of configurations and third-order nonlinear optical properties of C(36) and C(34)X(2) (X=B,N)

Using the ab initio method, the geometrical structures of C(36) and the X (B,N)-doped isomers C(34)X(2) have been optimized. On the basis of the optimized structures, then, the third-order nonlinear optical polarizabilities gamma in the different optical processes of the third-harmonic generation, electric-field induced second-harmonic generation and degenerate four-wave mixing, and two-photon absorption (TPA) cross sections delta are calculated by using TDB3LYP method coupled with the sum-over-states method. The calculated results show that the one-photon allowed excitation process dominate the two-photon excitation process for C(36)-D(6h), whereas the two-photon allowed excitation process dominate the one-photon excitation process for C(36)-D(2d) and C(34)X(2) (B,N). It is found that the largest resonant TPA peaks of dopant fullerenes have a blueshift and the TPA cross sections have an enhancement compared with those of the parent fullerenes of isomers C(36)-D(6h) and C(36)-D(2d).     

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.     

Structures,vibrational spectra,and relative energies of HXSiS (X = H,F, and Cl) isomers

The potential energy surface for the decomposition of HXSiS (X = H, F, and Cl) on the singlet state has been explored by B3LYP and CCSD(T) calculations. Five different types of reaction are proposed: (A) 1,1‐HX elimination, (B) 1,2‐H shift, (C) 1,2‐X shift, (D) H · and XSiS · radical formation, and (E) X · and HSiS · radical formation. These results show interesting trends for the HXSiS isomers. Our theoretical investigations suggest that the doubly bonded species HXSiS should be the lowest energy structure among the isomers from both kinetic and thermodynamic viewpoints. We also report theoretical predictions of molecular parameters and vibrational infrared (IR) spectra of the monohalogen‐substituted silanethione, which should be useful for future experimental observations. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 14–25, 2001     

Ab Initio calculations of the stabilization energies of the conformational and the structural isomers of C(3)H(7)X where X = F,Cl, and Br

HF, MP2, and B3LYP calculations with different basis sets have been used in the computation of the stabilization energies of C(3)H(7)X isomers, where X is F, Cl, and Br. The experimental stabilization energies of the structural isomers of C(3)H(7)Cl and C(3)H(7)Br have been reproduced via B3LYP calculations. However, the calculated stabilization energies of fluoropropane isomers from their reported enthalpies of formation have been reproduced in all methods of calculations in present work. The experimental relative stabilities of the gauche conformers of 1-fluoro-, 1-chloro-, and 1-bromopropanes have been also reproduced via some of the used calculations in the present work. The effect of the geminal interactions on X atomic charges and on the C-X and C-C bond lengths in halopropane isomers are also discussed.     

Theoretical study on structures and stabilities of N4X (X = O,S, Se,Te) series

The stable and transition structures of N₄X (X = O, S, Se, Te) series with singlet state are optimized with the ab initio (MP2) and density functional theory (B3LYP) methods using the 6‐311+G(d) basis set. The ring isomers are found to be the global minima for N₄O, N₄S, N₄Se, and the chain isomer is the minimum for N₄Te. The stabilities are studied by evaluating the dissociation barriers with respect to dissociation. The reactants and products connected by transition structures are determined by applying the intrinsic reaction coordinate (IRC) calculations. The C_2v, C_3v and ring isomers decompose into linear NNX and N₂ molecules, however, the chain isomers decompose into cyclic N₂X and N₂ firstly. A new possible isomerization mechanism between the cyclic and linear structures of N₂X series is studied. The cyclic structures of N₂X convert into linear structures easily with the very low barriers. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical study of aromaticity in small hydrogen and metal cation clusters X (X=H,Li, Na,K, and Cu)

Five cation clusters X (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D_3h) and linear structure (D_∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D_3h) is stable. The related neutral clusters X₃Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H₃Cl species, there is no a stable structure to be found. For other four X₃Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C_2v‐1) [see Fig. 1 (d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Quantum-chemical Study on the Structures and Properties of Uracil-BX3 （X = F, Cl） Complexes

1 INTRODUCTION The intermolecular interaction of bases in DNA or RNA is of immense interest and significance to che- mists and biologists alike. The interactions of these bases with metal cations, solvent molecules and other small molecules or ions would affect the struc- ture and biological properties or recognition process,which has been investigated widely[1～8]. Boron contained compounds are electron deficient com- pounds and have been extensively used as catalysts in chemical react…     

Theoretical study of the geometric and electronic structure of neutral and anionic doped silver clusters, Ag5X with X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni

Density functional theory (DFT) has been applied to investigate the low-lying electronic states of neutral and anionic transition metal doped silver clusters Ag₅X^0,− with X = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni using the B3LYP functional with the Stuttgart SDD basis sets. The structural features, frontier orbital energy gaps (HOMO and LUMO), vertical detachment energies, and vertical and adiabatic electronic affinities are evaluated. For all doped silver clusters, both in neutral and anionic states, two-dimensional and three-dimensional low-energy isomers are found to coexist. For neutral clusters, dopant Sc, Ti, V, and Mn atoms largely decrease the frontier orbital energy gaps, while they are markedly increased by Sc and Fe atoms in the anionic clusters. A completely quenched dopant magnetic moment is found in Ag₅Sc, while high spin magnetic moments are located on the other dopant atoms in Ag₅X^0,−.     

Theoretical Investigation on the Geometries and Properties of Guanine-BX3 （X = F, Cl） Complex

Geometries and binding energies were predicted at the B3LYP/6-311+G* level for the guanine-BX3 (X = F, Cl) systems and four isomers with no imaginary frequencies have been obtained for both guanine-BF3 and guanine-BCl3, respectively. Single energy calculations using much larger basis sets (6-311+G(2df,p) and aug-cc-pVDZ were carried out as well. It was found that the most stable isomer of guanine-BF3 is BF3 connected to N3 of guanine with the stabilization energy of –19.93 kcal/mol (BSSE corrected), while that of guanine-BCl3 is BCl3 connected to O10 of guanine having stabilization energy of –15.02 kcal/mol at the same level. The analyses for the combining interaction between BX3 and guanine with the atom-in-molecules theory (AIM) and natural bond orbital (NBO) methods have been performed. The results indicated that all the isomers are formed with σ-p type interactions between guanine and BX3, in which pyridine-type nitrogen or carbonyl oxygen or nitrogen atom of amino group offers its lone pair electrons to the empty p orbital of boron atom and the concomitance of charge transfer from guanine to BX3 has occurred. Still, one or two hydrogen bonds exist in some isomers of guanine-BX3 system and contribute to the stability of complex systems. Frequency analysis suggested that the stretching vibration of BX3 undergoes a red shift in complexes. Guanine-BF3 complex is more stable than guanine-BCl3 although the B–Y (Y=N, O) bond distance in the latter is shorter.     

CAl4X (X=Si,Ge): molecules with simultaneous planar tetracoordinate carbon, aluminum, and silicon/germanium

The authors report the first theoretical study on the hexa-atomic molecules CAl(4)X (X=Si,Ge) at the B3LYP/6-311++G(2d), MP2/6-311++G(2d), and CCSD(T)/6-311++G(3df) (single point) levels. Three low-lying isomers (within 2.0 kcal/mol) can be formally viewed as constructed by one Al+ interacting with the planar CAl3X- at the side Al-X bond (X-1), side Al-Al bond (X-2), and central C atom (X-3). The isomers X-1 and X-2 both have planar structures that include the planar tetracoordinate carbon, aluminum, and silicon/germanium, while the three-dimensional isomer X-3 has the pentacoordinate carbon. The planarity of X-1 and X-2 is ascribed to the ligand five-center two-electron bonding molecular orbital, similar to the orbital responsible for the planarity of CAl3X- (X=Si,Ge). Kinetically, the two planar structures X-1 and X-2 can be easily interconverted to each other via the intermediate X-3, indicative of their coexistence. Of particular interest, isomer X-1 represents the first example that simultaneously contains three types of planar centers in a single molecule, to the best of our knowledge. The three low-lying and structurally interesting isomers X-1, X-2, and X-3 await future experimental verification. The present results could enrich the planar chemistry.     

Ab initio and DFT energetics of silylenic X–CNSi (X=H, F, Cl, and Br)

Singlet–triplet energy splitting for 24 silylenic reactive intermediates, X–CNSi (where X=H, F, Cl and Br), are compared and contrasted at 11 levels of theory: B1LYP/6-31++G**, B3LYP/6-31++G**, B1LYP/6-311++G**, B3LYP/6-311++G**, MP3/6-31G*, MP3/6-311++G**, MP2/6-31+G**, MP2/6-311++G**, MP4 (SDTQ)/6-311++G**, QCISD(T)/6-311++G** and CCSD(T)/6-311++G**. Each X-substituted silylenic species may either be singlet (s) or triplet (t), with one of the following three structures: 3-X-2-aza-1-silacyclopropenylidene (1_s-X, 1_t-X); [(X-imino)methylene]silylene (2_s-X, 2_t-X); and X-cyanosilylene (3_s-X, 3_t-X). For all X–CNSi species studied, orders of singlet–triplet energy separations (ΔE_s-t,X), appear as a function of electro-negativity (F>Cl>Br>H). For the six H–CNSi isomers (X=H), stability order is: 3_s-H>1_s-H>2_t-H>3_t-H>2_s-H>1_t-H. Likewise, stability order for the six isomers with X=F, is: 3_s-F>3_t-F>1_s-F>1_t-F>2_s-F>2_t-F. For X=Cl, the order of stability is: 3_s-Cl>1_s-Cl>3_t-Cl>2_t-Cl>1_t-Cl>2_t-Cl. Finally, the order of stability for six isomers of Br–CNSi is: 3_s-Br>3_t-Br>1_s-Br>2_s-Br>2_t-Br>1_t-Br. The lowest energy minimum, among all 24 species scrutinized, appears to be the singlet acyclic 3_s-X. Triplet silylene 2_t-H is suggested to be more stable than its corresponding 2_s-H at MP3, MP2 and DFT levels of theory. Comparisons between relative stabilities; multiplicities and geometrical parameters of 1–3 are discussed.     

Relationships between NMR shifts and interaction energies in biphenyls,alkanes, aza-alkanes,and oxa-alkanes with X─H…H─Y and X─H…Z (X,Y = C or N; Z = N or O) hydrogen bonding

Hydrogen–hydrogen C─H^…H─C bonding between the bay-area hydrogens in biphenyls, and more generally in congested alkanes, very strained polycyclic alkanes, and cis-2-butene, has been investigated by calculation of proton nuclear magnetic resonance (NMR) shifts and atom–atom interaction energies. Computed NMR shifts for all protons in the biphenyl derivatives correlate very well with experimental data, with zero intercept, unit slope, and a root mean square deviation of 0.06 ppm. For some congested alkanes, there is generally good agreement between computed values for a selected conformer and the experimental data, when it is available. In both cases, the shift of a given proton or pair of protons tends to increase with the corresponding interaction energy. Computed NMR shift differences for methylene protons in polycyclic alkanes, where one is involved in a very short contact (“in”) and the other is not (“out”), show a rough correlation with the corresponding C─H^…H─C exchange energies. The “in” and “in,in” isomers of selected aza- and diaza-cycloalkanes, respectively, are X─H^…H─N hydrogen bonded, whereas the “out” and “in,out” isomers display X─H^…N hydrogen bonds (X = C or N). Oxa-alkanes and the “in” isomers of aza–oxa-alkanes are X─H^…O hydrogen bonded. There is a very good general correlation, including both N─H^…H─Y (Y = C or N) and N─H^…Z (Z = N or O) interactions, for NH proton shifts against the exchange energy. For “in” CH protons, the data for the different C─H^…H─Y and C─H^…Z interactions are much more dispersed and the overall shift/exchange energy correlation is less satisfactory.     

密度泛函方法研究HS2X的稳定构型

采用量子化学中的密度泛函理论(DFT),在B3LYP／6-311 G(3df,2p)水平上全优化得到了单卤代二硫烷HSSX(X-H,F,Cl,Br)链型和分叉型两种异构体的平衡结构。计算结果表明．在热力学上,所有链型的HSSX为稳定构型．其能量分别较分叉型构型低109．8、60．2、74．8和73．1kJ／mol。同时,采用统计热力学方法,研究了两种平衡结构之间相互转化的化学热力学性质,发现异构化反应的平衡常数很小。     

Search for more stable C58X18 isomers: stabilities and electronic properties of seven-membered ring C58X18 fullerene derivatives (X = H, F, and Cl)

Stimulated by recent preparation and characterization of the first C58F18 fullerene derivative, with a heptagon in the framework (Science, 2005, 309, 278), we have performed systematic density functional studies on the stabilities and electronic properties of two different structures C58X18 (A) and C58X18 (B), where X = H, F, and Cl. The large energy gaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (between 2.64 and 3.45 eV) and the aromatic character (with nucleus independent chemical shifts from -10.0 to -13.9 ppm) of C58X18 (A) and C58X18 (B) indicate that they possess high stabilities. Further investigations show that the heats of formation of C58X18 fullerene derivatives are highly exothermic, suggesting that adding nine X2's releases much of the strain of pure C58 fullerene and leads to stabilities of the derivatives. Lower in energy and stronger in aromatic character than C58F18 (B), which has been experimentally characterized, C58F18 (A) should also be isolated. In addition, C58F18 and C58Cl18 are predicted to possess large electron affinities, especially for C58F18 (B) and C58Cl18 (B) with values of 3.00 and 3.06 eV, respectively, even larger than that (2.50 eV) of C60F18. Hence, C58F18 and C58Cl18 can serve as good electron-acceptors with possible photonic/photovoltaic application. The IR spectra of C58X18 are simulated to facilitate identification of different isomers experimentally. In addition, the electronic spectra and second-order hyperpolarizabilities of C58X18 are predicted by ZINDO and sum-over-states model. With the addition of 9X2, both the static and frequency-dependent second-order hyperopolarizabilities of C58X18 greatly decrease compared to those of C58.     

Nonplanarity at tri-coordinated aluminum and gallium: cyclic structures for X3Hn(m) (X = B, Al, Ga)

Structures and energies of X3H3(2-), X3H4-, X3H5, and X3H6+ (X = B, Al and Ga) were investigated theoretically at B3LYP/6-311G(d) level. The global minimum structures of B are not found to be global minima for Al and Ga. The hydrides of the heavier elements Al and Ga have shown a total of seven, six and eight minima for X3H3(2-), X3H(4-), and X3H5, respectively. However, X3H(6+) has three and four minima for Al and Ga, respectively. The nonplanar arrangements of hydrogens with respect to X3 ring is found to be very common for Al and Ga species. Similarly, species with lone pairs on heavy atoms dominate the potential energy surfaces of Al and Ga three-ring systems. The first example of a structure with tri-coordinate pyramidal arrangement at Al and Ga is found in X3H(4-) (2g), contrary to the conventional wisdom of C3H3+, B3H3, etc. The influence of pi-delocalization in stabilizing the structures decreases from X3H3(2-) to X3H6+ for heavier elements Al and Ga. In general, minimum energy structures of X3H4-, X3H5, and X3H6+ may be arrived at by protonating the minimum energy structures sequentially starting from X3H3(2-). The resonance stabilization energy (RSE) for the global minimum structures (or nearest structures to global minimum which contains pi-delocalization) is computed using isodesmic equations.     

The interaction between C28 (Td) and X (X=H and F)

Hydrogen and fluorine addition reactions with C₂₈(T_d) have been investigated by the density function theory method at B3LYP/6-31G level. The interaction potential between C₂₈(T_d) and atom X (X=H and F) shows that there are three possible stable isomers of C₂₈(T_d)X (X=H and F) and the average binding energy calculations suggest that C₂₈(T_d)H₄ is the most stable hydrogen adduct among C₂₈(T_d)H_n (n=1–28). Furthermore, by comparisons of the energy between C₂₈(T_d)H and C₂₈(C_s)H we found that the former are more stable than the later, and the structural and energy analysis further indicate that C₂₈(C_s)H is only with a small distortion of C₂₈(T_d)H symmetry. In addition, the transition states, as well as reaction pathways of X transfer reactions between different key points on C₂₈(T_d) representative patch are given to explore the possible reaction mechanism.