BH4中性分子和离子结构的量子拓扑研究

采用密度泛函方法B3LYP和耦合簇方法CCSD分别在6-311+G(d,p)水平上对BH4+、BH4和BH4−的构型进行全优化, 并从量子拓扑学的角度对各稳定构型进行电子密度拓扑分析. 研究表明, BH4+、BH4和BH4−分别具有C2v、C2v和Td对称性. BH4+和BH4中都存在B—H键、H—H键和原子-分子键；而BH4−中存在着四个相同的B—H键；BH4中含有未成对电子, 其主要围绕B原子运动.     

5d过渡金属原子中心镶嵌Ag团簇M@Ag12(M＝Hf～Hg) Ih和Oh构型的密度泛函理论研究

采用相对论密度泛函理论方法对Ih和Oh构型M@Ag12 (M＝Hf～Hg)的几何和电子结构进行了系统的研究. 研究表明, 原子半径之和与团簇的电子结构共同决定了M—Ag键长的大小. M@Ag12的成键能来自中心原子的嵌入能和Ag12笼子的形变能. 最高占据轨道为成键轨道的团簇比反键轨道的团簇的稳定性强. 我们发现在此系列中, Ih构型不一定总比Oh构型稳定. Hf@Ag12, Ir@Ag12, Au@Ag12和Hg@Ag12的Oh构型比Ih构型稳定.     

AlmN2和AlmN+2(m=1～8)团簇结构与稳定性的量子化学研究

用密度泛函理论(DFT）的B3LYP方法，在6-311G水平上AlmN2和AlmN^ 2(m=1～8)团簇的几何构型、电子结构、振动频率和分子轨道进行了理论研究．结果表明，AlmN2类团簇的基态结构有两种基本构型，一种是以N-N键为核心周围与Al原子相配位形成的，一种是由两个AlnN(n≤m，2)分子碎片通过共用Al原子或Al—Al键相互结合形成的．对AlnN分子碎片相互结合形成结构的绝热电离能讨论得到，m为偶数的团簇比m为奇数的稳定。     

金钯二元小团簇的几何结构与电子性质

在UBP86/LANL2DZ和UB3LYP/def2-TZVP水平下详细研究了AumPdn(m+n≤6)团簇的几何结构和电子性质.阐明了团簇的结构特征、平均结合能、垂直电离势、垂直电子亲和能、电荷转移以及成键特征.除单取代混合团簇(AunPd和AuPdn,n=5或6)外,五和六原子混合团簇中钯原子趋于聚集到一起形成Pdcore,金原子分布在Pdcore周围形成PdcoreAushell结构.含一个和两个钯原子团簇的电子性质与纯金团簇类似,呈现一定奇偶振荡.混合团簇的电子性质,如最高占据分子轨道(HOMO),最低未占据分子轨道(LUMO),垂直电离势,垂直电子亲和能,Fermi能级和化学硬度等均与团簇空间结构和金、钯原子数之比直接相关.混合团簇中存在钯原子到金原子间的电荷转移,表明团簇中存在明显金钯间成键作用.分析团簇的电荷分布、前线轨道和化学硬度表明,金钯混合团簇对小分子如O2、H2和CO等的反应活性要强于纯金团簇.     

Au12M (M=Na,Mg, Al,Si, P,S, Cl)团簇的结构、稳定性和电子性质

采用基于密度泛函理论的第一性原理方法系统地研究了Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇的结构、稳定性和电子性质.对团簇的平均结合能、镶嵌能、垂直离化势、最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)的能级差、电荷布居分析、自然键轨道(NBO)进行了计算和讨论.对于Au12M(M=Na,Mg,Al)团簇,它们形成了内含M原子的最稳定的笼状结构.然而对于Au12M(M=Si,P,S,Cl)团簇,它们却形成了以M元素为顶点的稳定锥形结构.在这些团簇中发现Au12S团簇相对是最稳定的,这是由于Au12S团簇形成了稳定的满壳层的电子结构.自然电荷布居分析表明:对于所有的Au12M(M=Na,Mg,Al,Si,P,S,Cl)团簇电荷总是从Au原子转向M原子.自然键轨道和HOMO分析表明Au12M团簇中发生了Au原子的s-d轨道和M原子的p轨道间的杂化现象.     

用密度泛函理论研究纳米级的硼簇Bn（n=13～20）的物理和化学性质

采用密度泛函理论B3LYP与6—311＋＋G方法研究了硼簇Bn（n=13～20）的电子和几何结构、总能量、结合能、谐波频率、点对称性、电荷分布、偶极矩、化学键以及最高分了占据轨道和最低分子占轨道能量差．此外,借助第一和第二能级差确定最稳定的硼簇尺寸．研究表明硼簇几乎所有的物理性质有尺寸依赖性,双环管状结构的B20具有最高平均结合能．内有一原子的二十面体结构的B13不具有稳定构型,这种结构转变为开放式笼状．B20出现二维到三维的结构转变．Mulliken分析表明电荷分布有x-z和y-z平面对称．硼簇的平面稳定性可以通过离域键（π键和σ键）以及多中心键来解释．     

[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（AuPH3）m]^n＋（m=4-6；n=0-2）的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。     

钴硫团簇ConSn+-1(n=2,3)的结构和稳定性

用ab initio分子轨道方法(RHF,UHF)和密度泛函(DFT)方法研究了团簇Co2S+,Co3S2+的各种可能的几何构型和电子结构,并计算了相应的较稳定构型的振动光谱,发现Co2S+和Co3S2+团簇最稳定结构均具有C,对称性.对团簇的成键作用机理进行了理论分析.     

希土冠醚配合物的电子结构

本文用INDO方法计算了希土冠醚配合物的分子构型、电子结构、电荷分布和键级,讨论了配位前后电荷分布特征,以及由于配位引起L→L_n电荷转移跟配合物电子结合能化学位移和配位活化的关系,解释了因冠醚内腔不同希土冠醚配合物呈现不同构型的内在原因。希土冠醚配合物的占据分子轨道以配位体轨道成分为主体(4f轨道除外),低空轨道以希土原子轨道成分为主体。其占据分子轨道可分为六组。冠醚环上引入苯环后配合物前线轨道呈现π键性质。其价键的主要贡献部份是5d轨道,其次是6p和6s。4f轨道基本上不参与成键。讨论了配合物的化学键性质及高配位数时稳定的因素。     

Local density functional study of the structural and electronic properties of C60 and XC60 (X=K, Rb, Cs)

Results of first principles local density total energy and atomic force calculations carried out for free C₆₀ and XC₆₀ (X=K, Rb, Cs) molecular clusters are reported. The optimization of the geometry results in the bond lengths between adjacent carbon atoms being 1.387 and 1.445 Å, which are in very good agreement with the latest X-ray diffraction values. Energy levels, charge distributions, and wavefunction characteristics are obtained and discussed. The results for C₆₀ are in very good agreement with recently measured photoemission energy distribution curves (EDC) for the valence band states. The highest occupied molecular orbitals (HOMO) are found to be fully occupied H_u states and are 1.7 eV below the lowest unoccupied molecular orbitals (LUMO) which are of T_1u symmetry. Similar results obtained for the XC₆₀ clusters show that rigid-band-like behavior is found in the electronic structures after putting an alkali atom at the center of a C₆₀ ball. In each case, the alkali atom is almost fully ionized with the transferred electron distributed over the surface shell of C₆₀; the center region of the ball has very low charge density.     

Theoretical study of C24N4 molecule

Both ab initio 6-31G, 3-21G and STO-3G basis sets and semiempirical PM3 and AM1 molecular orbital calculations are carried out on the C₂₄N₄ molecule of the T_d symmetry group. Results on the fully optimized structure which constrained T_d symmetry, molecular orbitals and vibrational frequency were obtained by both ab initio and semiempirical methods. The binding energy and various thermodynamic properties were also calculated via the PM3 and AM1 semiempirical methods. All the evidence of this work proves that the C₂₄N₄ molecule is stable and that its four six-membered rings with a remarkable delocalized C…C bond are similar to the related rings in the C₆₀ buckminsterfullerene structure.     

An electron transfer mechanism of O4 formation

A resonating valence bond electron transfer mechanism of combining two O₂ molecules to form an O₄ molecule is presented. The predicted molecular states of the reaction path D_∞h→C_2v→D_2h are supported by the present ab initio molecular orbital calculations. The CASPT2 BSSE calculations yield a stable diamagnetic D_2h O₄ molecule with a very weak chemical bond between the monomers, in good agreement with experiments. A low activation barrier energy of 26 cal/mol for the O₄ formation is found.     

Super-valence phenomenon of carbon atoms in C20 molecule

Fourteen structures of C₂₀ are studied at DFT/B3LYP/6-31G* theoretical level. Except ring, bowl, cage and isomer 1 which have been studied before, other isomers have not been reported so far. Calculated results show that the ring has the lowest energy at this level and isomers 1, 2, 3 and 4 have lower energies than that of cage. Analyses of optimized bond lengths, electronic structure indicate that some carbon atoms express super-valence property. In addition, NICS value is consistent with molecular orbital character in denoting aromaticity of C₂₀ molecule. Delocalization character averts influence of curvature strain, which can well explain the stability of the cage.     

Unique selectivity for the dimerization of propene on RhSn/SiO2 catalysts: implications on the mechanism of C---C bond formation and cleavage on bimetallic catalysts

A series of bimetallic catalysts RhSn_x/SiO₂ (x = 0.4, 0.7, 0.9, and 1.4) were synthesized by the reaction of the monometallic catalyst Rh/SiO₂ with Sn(n-butyl)₄ under hydrogen. Various chemical and spectroscopic methods indicated that the metals present were fully reduced, and that tin atoms rest on the surface, very slightly increasing particle size and producing isolated rhodium sites. The catalytic reactions of propylene/hydrogen mixtures in the presence of these bimetallic catalysts are compared with those of the monometallic Rh/SiO₂ catalysts. The mechanistically interesting reactions observed are those of carbon-carbon bond formation and cleavage. For the monometallic catalyst, olefin homologation and hydrogenolysis were observed, reactions which invoked the transfer of C₁ fragments from one olefin to another. For the bimetallic catalysts, a marked increase in the selectivity for C₆ products was observed. The presence of hydrogen is necessary to this reaction but selectivity for C₆ is enhanced when hydrogen is in deficit with respect to propylene. Selectivity for C₆ increases with the surface rhodium to tin, Rh^s/Sn, ratio to a maximum at 0.9. Low temperature favors the formation of C₆ and C₂ products.     

基于曲率和电子结构的掺杂C50和C70富勒烯的稳定性研究

使用密度泛函理论(DFT)-B3LYP/6-31G^*方法研究了B、N、Si、P和Co在C₅₀和C₇₀中的掺杂能和电子结构, 并基于曲率理论和电子结构探讨了掺杂富勒烯的结构稳定性. 计算结果表明, 掺杂能随着原子曲率的增大而减小, 随着掺杂物种原子半径的增大而增大, B、N、P和Co的掺杂有利于C₅₀结构的稳定, 而B和N的掺杂不利于C₇₀结构的稳定; 除了用于反映原子活性的曲率主要决定掺杂反应性, 各不等价碳原子在C₅₀和C₇₀的最高占据分子轨道(HOMO)中所占成分对掺杂能的影响也很大, 且其成分越大越有利于掺杂. 此外, 掺杂原子得失电子情况与其电负性有关. 本工作将为富勒烯结构稳定性的研究提供理论依据.     

Stereochemistry of the Heterocyclic Alcohols Containing Piperidine Unit

The stereochemistry of the heterocyclic alcohols (R₁-OH~R₄-OH,see Fig.1) containing piperidine unit has been studied on the basis of the calculations of molecular mechanics and quantum chemistry. The calculations of alcohols (R₁-OH~R₄-OH) and their carboxylate derivatives were carried out, and the results of these calculations were listed in Tab.1 and Tab.2. It was showed that there existed the non-classical orbital super-conjugated interactions between the nitrogen atom and oxygen atom which caused the conformations to be more stable when the hydroxylic group lay at axial than at equatorial with respect to the piperidine ring in compounds (R₁-OH) and (R₃-OH). If the axial hydrogen atoms at C₂ and C₆ positions in the piperidine ring were substituted, or the molecular existed in the polar solutions, this non-classical orbital super-conjugated interactions would be much weak even diminished. In this case,the conformations were more stable when the hydroxylic group at equatorial than at axial in these compounds. These consistented with the experimental results.     

Electronic structure and bonding in Si70

We report a detailed AM1 investigation of the geometrical and electronic structure of Si₇₀. For this purpose, bond lengths, bond orders, charges and molecular energy levels are widely analyzed, and compared with previous theoretical and experimental data on Si₆₀ and homologous carbon clusters C₇₀ and C₆₀. The predicted D_5h structure of Si₇₀ is less delocalized than that of C₇₀. Furthermore, Si₇₀ presents the lowest ionization potential (7.63eV), the highest electron affinity (3.61 eV) and the smallest HOMO-LUMO gap (4.02eV) of the four studied clusters.     

Structure and stability of thiourea with water, DFT and MP2 calculations

The relative stabilities of thiourea in water are investigated computationally by considering thiourea–water complexes containing up to 1–6 water molecules (CS(NH₂)₂(H₂O)_n=1–6) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H₂O molecule is about 33 kJ mol⁻¹ for n=1–5.The C–S bond, N–C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H₂O molecules. As the solvation progresses, the C–S distance increases monotonically while the Mulliken populations on the C–S bond reduces monotonically with the addition of each H₂O molecule, indicating that the C–S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H₂O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea.     

Stable structures of oxocarbons and pseudooxocarbons of group VI

Density functional theory has been used to study the geometries, electronic structure and harmonic vibrational frequencies of the oxocarbons and the pseudooxocarbons of group VI. The ability of the maximum hardness principle for predicting the stable structures of oxocarbons and pseudooxocarbons of group VI is tested by analyzing the results of these calculations. To obtain the stable structure, the geometrical parameters and stability of molecules are compared and analyzed. Bond orders of candidate molecules are calculated by using natural bond orbital analysis. Except selenium derivatives, atoms in molecule calculations prove being useful for studying the nature of carbon heteroatom bond. Chemical hardness is also reported. This study reveals that (1) DFT gives very similar geometries and energies to ab-initio methods and (2) the maximum hardness principle (MHP) is not verified for some of these structures. Data for C₆Se₆, which are new, are presented in this work.