LiBH4-X（X=O,F和Cl）体系解氢性能的第一原理计算

采用基于密度泛函理论的第一原理方法,计算了LiBH4-X(X=O,F和Cl)体系的晶体与电子结构及解氢性能.生成热和H原子解离能的计算结果表明:O原子掺杂优先占据LiBH4间隙位,F置换氢原子位,而Cl则取代BH4单元;O,F和Cl掺杂的LiBH4体系结构稳定性发生变化,其中O提高体系解氢效果明显,而F和Cl掺杂受H原子区域环境的影响.态密度、Mulliken电子占据数和电子密度的分析结果表明:B—H之间较强的共价键是LiBH4结构稳定、解氢困难的电子结构根源,O,F和Cl对LiBH4解氢能力影响主要是掺杂改变了H的s态与B的sp态的杂化特性、以及BH4单元与Li的成键作用.     

6,12-二乙炔基茚并[1,2-b]芴系列衍生物的非线性光学性质

采用密度泛函理论(DFT) CAM-B3LYP方法对6,12-二乙炔基茚并[1,2-b]芴系列衍生物的极化率(α_s)和第二超极化率(γ_s)进行研究. 结果表明, 此类分子具有较大的γ_s值. 用乙炔基硅烷基和氧原子取代茚并[1,2-b]芴分子6,12位的氢原子后, 分子的几何构型发生改变, 进而影响其非线性光学(NLO)性质. 连接乙炔基硅烷基的分子α_s值和γ_s值均增大, 而连接氧原子的分子α_s值和γ_s值均减小. 茚并[1,2-b]芴环2,8位取代基R(R=H, F, CH₃)的不同, 对分子的γ_s值也有一定的影响, R为CH₃时分子的α_s值和γ_s值均较大. 由含时密度泛函理论(TD-DFT)方法计算的吸收光谱分析可知, 与茚并[1,2-b]芴系列分子相比, 引入乙炔基硅烷基的分子共轭性增强, 最大吸收波长红移; 引入氧原子的分子几何结构扭曲, 共轭性降低, 最大吸收波长蓝移.     

Mg取代对LiBH4（010）面结构和储氢性能的影响

采用基于密度泛函理论的第一性原理,研究了Mg取代Li原子对LiBH4(010)面的晶体结构、H原子解离能及H原子迁移的影响.结果发现,Mg取代后B—H键长增大,更易于H原子的解离.氢空位的出现也使其附近H原子的解离能减小.电子结构计算结果表明,Mg取代Li原子后,减弱了B—H之间的共价作用.通过对氢原子在[BH4]单元之间扩散能垒的计算发现,Mg取代Li原子后,H原子的扩散能垒由4.84 eV降为3.01 eV,表明H原子在体相内更容易迁移.     

含氮ZSM-5分子筛骨架中氮取代位置的密度泛函计算

运用Gaussian 98程序包, 采用密度泛函理论B3LYP方法, 基于ZSM-5分子筛的8T模型, 分别通过6-31G, 6-31G(d)和6-311G(d,p)基组计算了ZSM-5分子筛中氮原子取代前后各O原子和各N原子的能量, 从而得到各O原子与各N原子在骨架中的稳定性及其对氮化取代反应的影响. 计算结果表明, N原子在骨架中的稳定性对氮取代反应的影响较大. ZSM-5分子筛晶体结构中与B酸位处于同一个四面体的O11位置, 为氮原子的最佳取代位置, 因此氮化后分子筛表面的B酸强度得到较大程度的减弱.     

氟硼二吡咯类pH荧光探针PET光谱特性的理论计算

氟硼二吡咯(BODIPY)类pH荧光探针分子是基于光诱导电子转移(PET)的荧光探针分子, 识别基团氮原子上引入不同取代基可呈现不同的光学灵敏度. 本文应用密度泛函理论(DFT)及含时密度泛函理论(TD-DFT)方法对六种含不同取代基的探针分子进行了几何构型优化及激发态计算, 探讨了不同取代基对PET效应影响. 计算结果表明: 基态时这些探针分子的最高占有分子轨道(HOMO)和最低未占有分子轨道(LUMO)都在荧光母体BODIPY的π, π^*轨道, 而识别基团上氮原子孤对电子所在的轨道为HOMO-1轨道. 但是在激发态, 当氮原子上有两个取代基时, HOMO-1→LUMO跃迁的激发能都小于荧光团的HOMO→LUMO跃迁, 这将有可能产生PET效应并导致荧光熄灭, 而当氮原子上有一个取代基时不会出现这种现象. 通过激发态结构优化可以发现, 无论识别基团氮原子上有一个还是两个取代基, N原子的轨道对称性都发生变化, 由sp³→sp², 孤对电子占据在p轨道上, 其轨道能级升高至荧光团的HOMO和LUMO轨道之间, 将导致不同程度的PET效应, 与实验结果一致.     

取代基对依布硒啉电子结构及光谱性质影响的理论研究

采用密度泛函理论B3LYP方法在6-311++G**水平对依布硒啉及其6个衍生物进行结构优化,并分析了取代基对分子几何构型、电荷分布、前线轨道能级分布的影响.在相同计算水平上采用含时密度泛函理论方法进行了电子光谱研究,讨论了取代基对电子光谱的影响.计算结果表明,标题化合物分子为非平面结构,苯并异硒唑酮环与苯环之间存在一...     

C和As共掺杂的γ-Si3N4电子性质的密度泛函理论研究

采用密度泛函理论研究了C和As共掺杂的γ-Si3N4的电子性质. 当晶体中少量的四配位硅原子被碳原子所取代, 同时用少量的砷原子取代氮原子, 晶体结构的带隙可以被调整; 当n(C)/n(Si)≈0.063, n(As)/n(N)≈0.047时, 材料会发生绝缘体到金属的转变. 从态密度图中可以观察到价带顶端的能量明显上升. 讨论了关于这种共掺杂所引起的带隙较大减小的可能原因和潜在的应用.     

1-氟-1,1- 二氯乙烷与氟原子反应的理论研究

利用密度泛函理论研究了CH3CCl2F与F原子的反应机理.在MPW1K水平下计算了反应物、过渡态和产物的几何构型和频率,并进一步利用内禀反应坐标理论获得了反应的最小能量路径;在G3(MP2)水平下对所有驻点进行了单点能量校正.结果表明,CH3CCl2F与F原子的反应存在两个H迁移反应通道:CH2H′CCl 2F+F→C...     

甲基三氯硅烷水解反应机理的密度泛函研究

采用量子化学密度泛函方法研究了甲基三氯硅烷的结构性质和水解反应机理,发现水的O原子进攻Si原子取代Cl原子的同时,水的另一个H原子逐渐与Cl结合形成相应的羟基硅烷和HCl.甲基三氯硅烷水解按亲核取代--消除的协同反应机理完成.     

ZSM-5分子筛氮化的密度泛函理论研究

利用量子化学中的密度泛函理论,基于ZSM-5分子筛的8T簇模型,在Gaussian 98程序中采用B3LYP方法和6-311G(d,p)基组计算了ZSM-5分子筛中氮的最佳取代位置.计算结果表明,分子筛骨架中氧原子被氮原子取代的最佳位置为O11和O21位.由于位于B酸位上的O11原子是氮原子的最佳取代位置之一,所以氮化可以减弱分子筛表面的B酸强度.     

Mechanistic implications from the substitution reactions with methyl fluoride of photochemically produced hot tritium atoms

The reactions with CH₃F of photochemically produced tritium atoms from TBr have been studied at various wavelengths. The energy threshold is lower and the relative yield higher for F replacement than for H replacement in CH₃F. These near-threshold substitution reactions are consistent with an inversion mechanism.     

An ab initio study of 15N-11B spin-spin coupling constants for borazine and selected derivatives

Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond (11)B-(15)N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on (13)C-(13)C coupling constants for benzene.     

Ion size influence on the Ar solvation shells of M(+)-C6F6 clusters (M = Na, K, Rb, Cs)

The size-specific influence of alkali metal ions in the gradual transition from cluster rearrangement to solvation dynamics is investigated by means of molecular dynamics simulations for alkali metal cation-hexafluorobenzene systems, M(+)-C(6)F(6) (M = Na, K, Rb and Cs), surrounded by Ar atoms. To analyze such transition, different small aggregates of the M(+)-C(6)F(6)-Ar(n) (n = 1, ..., 30) type and M(+)-C(6)F(6) clusters solvated by about 500 Ar atoms are considered. The Ar-C(6)F(6) interaction contribution has been described using two different formalisms, based on the interaction decomposition in atom-bond and in atom-effective atom terms, which have been applied to study the small aggregates and to investigate the Ar solvated M(+)-C(6)F(6) clusters, respectively. The selectivity of the promoted phenomena from the M(+) ion size and their dependence from the number of Ar atoms is characterized.     

Synthesis, structure and theoretical study of mixed fluoro-trifluoromethyl derivatives of C60. Molecular structures of C60F18(CF3)6 and C60F16(CF3)6

A series of novel mixed C60Fn(CF3)m compounds has been produced by trifluoromethylation of C60F18 with CF3I in ampoules at 380-420 degrees C. Two of these compounds, C60F18(CF3)6 and C60F16(CF3)6, have been characterized by X-ray crystallography, which has revealed addition of six CF3 groups to the C3v-C60F18 for the former and replacement/elimination of two outermost F atoms in the latter. Quantum chemical calculations have been employed to predict the most stable possible isomers of C60F16/18(CF3)6 in order to rationalize the experimental results.     

Synthesis and polymerization ofSi-substituted silacyclobutanes

The synthesis and polymerization of silacyclobutane derivatives with ferrocenyl, 9-carbazolyl, and pentafluorophenyl fragments in substituents have been carried out. The effect of the replacement of H atoms by F in pendant groups of the polysiltrimethylene main chain on the glass transition temperature has been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2475–2478, December, 1995.     

C–F bond functionalizations of trifluoromethyl groups via radical intermediates

Selective functionalization of C–F bonds in trifluoromethyl groups has recently received a growing interest, as it offers atom-and step-economic pathways to access highly valuable mono-and difluoroalkylsubstituted organic molecules using simple and inexpensive trifluoromethyl sources as the starting materials. In this regard, impressive progress has been made on the defluorinative functionalization reactions that proceed via radical intermediates. Nevertheless, it is still a great challenge to p...     

Influence of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3 complexes

The effect of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH₃ (X = F, Cl, Br, OH, H, Me) and NCH···NH₃ complexes were investigated by quantum chemical calculations. Ab initio calculations were performed using MP2 method with a wide range of basis sets. With tacking into account the BSSE and ZPVE, the values of BEs decrease. Replacement of the nonparticipatory hydrogen atom of HCCH by the electronegative atoms (F, Cl, and Br), lead to the BEs increases. The BE corresponding to the replacement of the nonparticipatory hydrogen atom of HCCH by the OH and CH₃ groups decreases. A far greater enhancement of the interaction energy arises from replacement of HCCH by the more acidic HCN. The natural bond orbital analysis and the Bader's quantum theory of atoms in molecules were also used to elucidate the interaction characteristics of these complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. In addition, the relationship between the isotropic and anisotropic chemical shifts of the bridging hydrogen and binding energy of complexes as well as electron density at N···H BCPs were investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Infrared photochemistry of bis(trifluoromethyl) peroxide

Bis(trifluoromethyl) peroxide is readily dissociated by multiple infrared photon excitation at CO₂ laser wavelengths. The primary dissociation product is CF₃O; approximately 85% of the nascent radicals are further dissociated in the laser field to form CF₂O and F. The F atoms then react with the remaining CF₃O to produce CF₃OF. The formation of CF₃OF is strongly inhibited by addition of HI, which reacts preferentially with the F atoms.     

The Supramolecular Structural Chemistry of Pentafluorosulfanyl and Tetrafluorosulfanylene Compounds

The analysis of crystal structures of SF₅- or SF₄-containing molecules revealed that these groups are often surrounded by hydrogen or other fluorine atoms. Even though fluorine prefers F⋅⋅⋅H over F⋅⋅⋅F contacts, the latter appeared to be important in many compounds. In a significant number of datasets, the closest F⋅⋅⋅F contacts are below 95 % of the van der Waals distance of two F atoms. Moreover, a number of repeating structural motifs formed by contacts between SF₅ groups was identified, including different supramolecular dimers and infinite chains. Among SF₄-containing molecules, the study focused on SF₄Cl compounds, including the first solid-state structure analyses of these reactive species. Additionally, electrostatic potential surfaces of a series of Ph-SF₅ derivatives were calculated, pointing out the substituent influence on the ability of F⋅⋅⋅X contact formation (X=F or other electronegative atom). Interaction energies were calculated for different dimeric arrangements of Ph-SF₅, which were extracted from experimental crystal structure determinations.     

Structure and energy of Mo27SxCy clusters: a density functional theory study

For understanding the carburization processes of MoSx catalysts, the structures and energies of Mo27SxCy cluster models have been computed at the level of density functional theory. The surface sulfur atoms on the Mo edge and S edge as well as bulky sulfur atoms have been replaced by atomic carbon, and the corresponding structures have S/C ratios in the range of 0.8-55. The formation of all Mo27SxCy structures is favored thermodynamically. It is also found that the formation of CS and C2 bridging units is more favored than the individual or separated replacements and that the formation of C2 bridging units is more favored than that of CS units. In contrast, the replacement of sulfur on the Mo edge is least favored. Furthermore, the replacement of the bulky sulfur on the Mo edge is equally favored as those of sulfur on the S edge. For aiding further experimental studies, the C=S and C=C stretching frequencies have been computed.