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.     

Theoretical studies on fullerene C4o′s derivatives C4o X2 (X =H, F, Cl, Br)

应用密度泛函理论在B3LYP/6 31G*水平上对C40X2 (X=H,F,Cl,Br)进行研究.研究结果表明,C40X2 (X=H,F,C1,Br)在热力学上是稳定的,卤化衍生物的稳定性随卤素原子序数的增大而降低,最有利的衍生化方式是1-4加成,1-2与1-4加成的卤化和氢化衍生物在所研究的分子中较为稳定.这些研究有助于理解富勒烯衍生物的衍生化模式.     

金属四重键化合物M2X4(PMe3)4(M=Cr,Mo,W;X=F,Cl,Br,I)结构和电子光谱的密度泛函理论研究

采用密度泛函理论方法,在TZ2P-STO基组水平下,对金属四重键化合物M2Cl4(PMe3)4(M=Cr,Mo,W)和Mo2X4(PMe3)4(X=F,Cl,Br,I)的几何结构进行优化,分析了电子结构,并运用TDDFT方法对其低占据激发态进行了计算.考虑相对论效应的ZORA方法能够较好地重现M2X4(PMe3)4的几何结构.M2X4(PMe3)4的电子结构分析表明其d电子的组态为σ2π4δ2,前线轨道能级顺序为πlig<πd/σd<δd<δd*.金属原子和卤素配体的改变虽然使轨道能量发生变化,但没有影响轨道的排布顺序.TDDFT方法对M2X4(PMe3)4δd→δd*和πd→δd*跃迁能量的计算较为准确,对πlig→δd*(LMCT)跃迁能量的计算误差较大.金属原子、卤素配体以及相对论效应对激发能的影响可以根据分子轨道能级的变化给予解释.     

Ag_3XO_4(X=P,As,V)电子结构及光催化性质的第一性原理计算

基于密度泛函理论的第一性原理对Ag_3XO_4(X=P,As,V)电子结构及光催化性质进行了对比研究。与Ag_3XO_4相比,Ag_3VO_4较好的光催化稳定性主要源于其结构中Ag-O间较强的作用力增加了对Ag+的控制,而Ag_3VO_4弱的光催化活性与其导带底中存在d轨道成份以及较低的价带边势(2.335 V,vs NHE)有关;对Ag_3AsO_4而言,其优于Ag_3XO_4光催化活性的原因基于三个方面:(1)由高分散Ags-Ags杂化轨道构成的导带底能带;(2)窄的带隙(1.91 e V);(3)宽的可见光响应范围以及高的光吸收系数。此外,Ag_3XO_4(X=P,As,V)均为间接带隙半导体光催化材料,其中,Ag_3VO_4有用于分解水制氢研究的可能;上述计算结果与实验结果吻合。     

C40X2（X=H,F,Cl,Br）的理论研究

应用密度泛函理论在B3LYP/6-31G*水平上对C40X2(X=H,F,Cl,Br)进行研究.研究结果表明,C40X2(X=H,F,Cl,Br)在热力学上是稳定的,卤化衍生物的稳定性随卤素原子序数的增大而降低,最有利的衍生化方式是1-4加成,1-2与1-4加成的卤化和氢化衍生物在所研究的分子中较为稳定.这些研究有助于理解富勒烯衍生物的衍生化模式.     

Fe2+活化CH3X（X=H,Cl）中C—H,C—Cl键的理论研究

采用密度泛函理论(DFT)详尽地研究了Fe2+与CH3X(X=H,Cl)的反应机理.结果表明在所有通道中,反应4的H提取能垒最低(Ga=0.23 kcal/mol),氧化插入机制和SN2取代机制没有竞争性.详尽的电子结构分析表明由于金属3d与底物的σ*C—X可以最好的重叠,从而Fe2+从前端进攻C—X键有利于反应.该研究揭示了其微观本质,为Fe2+活化C—X键等相关研究提供理论线索和依据.     

杂硼原子簇B6X-(X=N, P, As, Sb, Bi)稳定性和芳香性研究

利用Gaussian 98程序, 采用从头算和密度泛函理论方法, 对B6X-(X=N, P, As, Sb, Bi)杂硼原子簇进行了理论研究, 优化得到了其稳定平衡构型, 讨论了其振动光谱和稳定性等, 通过自然键轨道(NBO)、分子轨道(MO)和核独立化学位移(NICS)分析, 确定这些杂硼原子簇都有离域的π电子和σ电子成键轨道, 满足4n+2电子规则, 具有芳香性, 与纯B6- 或B62- 原子簇呈反芳香性不同.     

[C(AuPH3)m]n+ (m=4-6; n=0-2)成键性质和稳定性研究

用MP2/LanL2DZ方法优化C(AuPH3)4[1a(C4v); 1b(Td)], [C(AuPH3)5]+[2a(C3h); 2b(Cs)]以及[C(AuPH3)6}]2+[3a(C2h); 3b(C2v)]的结构, 得到的几何参数与实验值相符. MP2水平下的自然键轨道(Natural bond orbitals, NBO)分析表明, Au具有d(sp)杂化性质, 其中(sp)具有s-p混合的轨道性质; 沿C-Au辐射方向形成的σ键和切向Au-Au之间的弱吸引相互作用使得整个分子稳定. 化合物1a, 2和3具有2或3个二电子三中心键, 表明该类化合物具有与传统C化学不同的电子结构和立体化学构型.     

C_4H_4Y(Y=O,S,Se)与BX_3(X=H,F,Cl)作用的计算化学研究

采用量子化学的密度泛函B3LYP和二阶微扰MP2(full)方法对C4H4Y(Y=O,S,Se)与BX3(X=H,F,Cl)形成的电子授受型复合物进行了研究,所得18个复合物的构型包括BX3位于C=C双键上方的π-p作用型和B与O,S,Se直接作用的n-p作用型.体系C4H4Y-BH3以n-p作用型较为稳定,体系C4H4Y-BF3,C4H4Y-BCl3的π-p和n-p作用型复合物稳定性相当.对各复合物的几何构型、振动频率和自然键轨道分析表明,复合物的形成过程中均存在几何构型的改变、电荷的转移和振动频率的变化,它们的变化规律与复合物稳定性的变化规律基本一致,即按H,F,Cl的顺序依次降低.     

饱和烷烃分子C_nH_(2n+2)(n=4-6)的电子动量光谱(英文)

使用B3LYP/TZVP//B3LYP/aug-cc-pVTZ方法系统研究了饱和烷烃分子CnH2n+2(n=4-6)的轨道电子动量光谱,比较了同分异构体CnH2n+2(n=4-6)对轨道动量分布的影响.结合二维空间分析方法对电子在坐标空间中的密度分布进行了系统的研究.计算结果表明,最内价壳层电荷分布主要由s电子贡献,第二近邻芯价壳层则主要由p电子贡献,而其余的价壳层则为sp杂化.最内价轨道表现出最大的谱线强度并且远大于其它轨道的谱线强度,而且正烷烃的谱线强度要大于异烷烃等同分异构体的谱线强度,表现出了明显的与甲基移动的个数有关的性质.     

theoretical study of tetrahydroborates and alanates L(MH4)4, HL(MH4)3, H2L(MH4)2, and H3L(MH4) (L = Al, Sc, Ti, V, Cr; M = B, Al)

The structural and energetic characteristics of the lowest-lying structures for isolated molecules and ions of light-metal boro- and aluminohydrides L(MH₄)₄, HL(MH₄)₃, H₂L(MH₄)₂, and H₃L(MH₄) (L = Al, Sc, Ti, V, Cr; M = B, Al) with different coordination modes of BH₄⁻- and AlH₄⁻ groups were calculated by the perturbation theory (MP₂), coupled cluster (CCSD(T)), and density functional theory (B3LYP) methods using the 6-31G*, 6-311+G**, and 6-311++G** basis sets. The results are compared with the computational data obtained at the same level of theory for related complexes L(MH₄)₃, HL(MH₄)₂, H₂L(MH₄), L(MH₄)₂, and HL(MH₄). The preferable coordination modes of the ligands in these complexes are analyzed, and the energies of dissociation with elimination of BH₃ (AlH₃) molecules and BH₄⁻ (AlH₄⁻) anions in various series of related hydroborates and hydroaluminates are estimated. The structure and relative stability of classical hydride and (μ-H₂)-hydrogen complexes in the H₂L (MH₄)₂ and H₃L(MH₄) systems are discussed. Original Russian Text ? O.P. Charkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 1015–1024.     

AB initio study of the regular polyhedral molecules N4, P4, As4, N8, P8 and As8

Ab initio pseudopotential SCF calculations were performed on tetrahedral X₄ molecules using double-zeta basis sets with and without d functions. The inclusion of d orbitals shortens the bond lengths, stabilizes the X₄ structures and intensifies the electron density inside the tetrahedron. The cubic X₈ molecules, calculated without d AOs, are not predicted to be more stable than 2X₄. Repulsions between parallel bonds in X₈ may compensate the lack of ring strain.     

Synthesis of the sulfones of leukotriene C4, D4, and E4

A simple one-step preparation of the sulfones of Leukotriene C₄, D₄ and E₄ has been developed by the direct oxidation of the parent compounds. An alternative synthesis of these sulfones has also been carried out by reduction of an acetylenic precursor.     

Zur struktur von CaPdF4, CdPdF4, HgPdF4 und HpPdF2

Single crystals of CaPdF₄ (purple) and CdPdF₄ (dark blue) have been obtained by heating CaF₂ (CdF₂) with PdF₂ at 820°C (900°C) for ca. 20–30 d in sealed Pd (Pt) tubes. CaPdF₄ crystallizes tetragonal (KBrF₄-Type) with a = 5.52₁, c = 10.57₀ Å (space group I4/mcm ? D^18_4h, No. 140) Z = 4, 283 unique reflexions, R = 0.083; R_w = 0.079, CdPdF₄ cubic (CaF₂-variant) with a = 5.40₃ Å (space group Pa3 ? T^6_h, No. 205) Z = 4, 165 unique reflexions, R = 0.047, R_w = 0.032. The high pressure modification of PdF₂, obtained by heating PdF₂ in closed Pt-tubes under a pressure of ≈ 60 kbar and ‘HgPdF₄’, both black, a = 5.32₇ Å and a = 5.43 Å are isotypic. CaPdF₄ is diamagnetic, CdPdF₄ and HPPdF₂ are antiferromegnetic.     

Phase formation in Cs2MoO4-MMoO4-Zr(MoO4)2 (M = Mn, Mg, Co, Zn) systems and crystal structure of new double molybdates Cs2MnZr2(MoO4)6 and Cs2MnZr(MoO4)4

Subsolidus phase relations in the Cs₂MoO₄-MMoO₄-Zr(MoO₄)₂ (M = Mn, Zn) ternary systems were determined, and two groups of new isostructural triple molybdates were synthesized: Cs₂MZr(MoO₄)₄ and Cs₂MZr₂(MoO₄)₆ (M = Mn, Mg, Co, Zn). Cs₂MnZr₂(MoO₄)₆ and Cs₂MnZr(MoO₄)₄ crystals were grown by spontaneous flux crystallization and used in structure solution for both groups of compounds. The Cs₂MnZr₂(MoO₄)₆ structure (a =13.4322(2) ?, c = 12.2016(3) ?, group R3, Z = 3, R = 0.0367) is a new structure type characterized by a mixed three-dimensional framework built of corner-sharing MoO₄ tetrahedra and (M, Zr)O₆ octahedra where large channels are occupied by cesium cations. Cs₂MnZr₂(MoO₄)₄ (a =5.3890(1) ?, c = 8.0685(3) ?, space group P $ \bar 3 $ \bar 3 m1, Z = 0.5, R = 0.0247) has the layered glaserite-like KAl(MoO₄)₂ type structure, where Al³⁺ octahedral positions are randomly occupied by a 0.5M²⁺ + 0.5Zr⁴⁺ mixture.     

The stereospecific synthesis of leukotriene A4 (LTA4), 5-epi-LTA4, 6-epi-LTA4 and 5-epi,6-epi-LTA4

The stereospecific syntheses of the four isomers of 6-formyl-5,6-epoxy hexanoic acid methyl ester $\text{8}$, $\text{15}$, $\text{23}$ and $\text{30}$ from Z-deoxy-D-ribose have allowed the preparation of methyl esters of LTA₄, $\text{1}$, and its three unnatural isomers.     

Ionic Mobility, Phase Transitions, and Superionic Conduction in Solid Solutions (100 ? x)PbF2-xZrF4 and Crystals K2ZrF6, (NH4)2ZrF6, KSnZrF7, and M(NH4)6Zr4F23 (M = Li, Na)

Methods of (¹⁹F, ¹H) NMR and impedance spectroscopy are used to investigate the internal mobility and ionic conduction in solid solutions arising in the system PbF₂-ZrF₄ and polycrystals KSnZrF₇, Li(Na)(NH₄)₆Zr₄F₂₃, and M₂ZrF₆ (M = K, NH₄). Factors responsible for the form of ionic motions and their energetics at 170–550 K are considered. It is established that the phase transitions in these compounds are connected with the crystal transition to a superionic state and that the high ionic (superionic) conductivity of beta phases is due to the diffusion of fluoride ions, ammonium cations, and possibly alkali metal cations. The obtained data testify to a substantial role of chainlike aggregation of anionic groupings and a variableness of structural mechanisms of formation of such chains in fluorozirconates for the development of translational diffusion in these compounds.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 573–582.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Goncharuk, Kotenkov, Tkachenko, Gerasimenko, Sergienko.     

Isomorphy of structural phase transitions in LiTaOSiO4, LiTaOGeO4 and titanite, CaTiOSiO4

Structural phase transitions in LiTaOGeO₄ (LTGO) and LiTaOSiO₄ (LTSO) have been observed using differential scanning calorimetry, X-ray diffraction and MAS NMR spectroscopy. LTGO transforms from P2₁/c to C2/c space group symmetry at , while the isomorphic transition occurs at in LTSO. An analogous phase transition is known to occur in the structurally related mineral titanite, CaTiOSiO₄. Spontaneous strain accompanying this phase transition in LTSO is significantly stronger than in titanite. As in titanite non-vanishing strain components are observable for T_c<T<T_i, with a similar ratio T_i/T_c. MAS NMR spectroscopy in combination with computation of the electric field gradient by first principle methods confirms that the tetrahedral Li coordination environment is retained during the phase transitions in LTGO and in LTSO. In LTSO substantial motional narrowing is observed, indicating increased mobility of the Li cation above . The narrowing of the spinning sidebands is significantly modified immediately above and below the critical temperature.     

Phase formation in the systems Li2MoO4-K2MoO4-Ln2(MoO4)3 (Ln=La, Nd, Dy, Er) and properties of triple molybdates LiKLn2(MoO4)4

Subsolidus phase relations in the systems Li₂MoO₄-K₂MoO₄-Ln₂(MoO₄)₃ (Ln=La, Nd, Dy, Er) were determined. Formation of LiKLn₂(MoO₄)₄ was confirmed in the systems with Ln=Nd, Dy, Er at the LiLn(MoO₄)₂-KLn(MoO₄)₂ joins. No intermediate phases of other compositions were found. No triple molybdates exist in the system Li₂MoO₄-K₂MoO₄-La₂(MoO₄)₃. The join LiLa(MoO₄)₂-KLa(MoO₄)₂ is characterized by formation of solid solutions.Triple molybdates LiKLn₂(MoO₄)₄ for Ln=Nd-Lu, Y were synthesized by solid state reactions (single phases with ytterbium and lutetium were not prepared). Crystal and thermal data for these molybdates were determined. Compounds LiKLn₂(MoO₄)₄ form isostructural series and crystallized in the monoclinic system with the unit cell parameters a=5.315-5.145 Å, b=12.857-12.437 Å, c=19.470-19.349 Å, β=92.26-92.98°. When heated, the compounds decompose in solid state to give corresponding double molybdates. The dome-shaped curve of the decomposition temperatures of LiMLn₂(MoO₄)₄ has the maximum in the Gd-Tb-Dy region.While studying the system Li₂MoO₄-K₂MoO₄-Dy₂(MoO₄)₃ we revealed a new low-temperature modification of KDy(MoO₄)₂ with the triclinic structure of α-KEu(MoO₄)₂¹ (a=11.177(2) Å, b=5.249(1) Å, c=6.859(1) Å, α=112.33(2)°, β=111.48(1)°, γ=91.30(2)°, space group , Z=2).     

Dirac-Fock one-centre calculations. The model systems TiH4, ZrH4, HfH4 and (104)H4

Relativistic and non-relativistic Hartree-Fock calculations including np and np and (n-1)d orbitals in the valence MO's are reported for the tetrahedral model systems TiH₄, ZrH₄, HfH₄ and (104)H₄. About 50%p and 50%d character is found, making the relativistic effects on the bond lengths and strengths one order of magnitude smaller than for the groups Ib, IIIb or IVb. This probably explains the close chemical similarity between Zr and Hf. The Ti---H bond length agrees with experiment. Inverted spin—orbit splitting is found to TiH₄.