LaC4团簇的理论研究

应用量子化学从头算方法研究了LaC4团簇，结果表明，在所提出的构型中，稀土位于碳环上最稳定，计算得到该团簇的绝热电子亲和势为81．05kJ/mol，离化能为628．88kJ/mol。该结果解决了实验中无法测定的问题，同时为合成实验提供了一定的理论指导。     

N-4-戊烯基硝酮分子内环加成反应区域选择性的理论研究

N-烯基硝酮分子内环加成反应具有区域选择性,如图1.当n=2,R~1=R~2=R~3=H时,即N-4-戊烯基硝酮分子内环加成反应.实验表明,P_a的产率为23％,P_b为47％.我们曾用MINDO/3方法对此反应进行IRC计算,确证P_a、P_b是经由反应物两种不同构象(R_a、R_b)分别得到的产物,并讨论了二反应活化势垒的差别对区域选择性的影响.Tufariello等人认为,P_b的较高产率主要由于2个产物的过渡态的熵差别.为此,本文从理论上考察活化熵和活化焓对区域选择性的影响.     

Reaction mechanisms of dissociative chemisorption of HI, I2, and CH3I on a magic cluster Al13-

We have investigated the transition-state structures and reaction mechanisms for the dissociative chemisorption reactions of HI, I(2), and CH(3)I on the magic cluster Al(-) (13). The HI, I(2), and CH(3)I molecules approach Al(-) (13) with an end-on orientation rather than a side-on orientation because of the more effective orbital overlap in the end-on orientation. The reactions of Al(-) (13) with HI and I(2) would produce Al(13)HI(-) and Al(13)I(2) (-), respectively, because of large exothermic energy changes and relatively small activation energies. The reaction of Al(-) (13) with CH(3)I is unlikely to take place because of the low mobility of CH(3) on Al(-) (13) and the high activation barrier for the S(N)2-type reaction. The dissociative chemisorption reactions are preferred thermodynamically to the abstractive chemisorption reactions.     

团簇Fe4P异构化反应的理论研究

采用B3LYP泛函以及程序内置的LANL2DZ基组并结合拓扑学原理,运用Gaussian 09程序对团簇Fe4 P的16种初始构型进行优化,得到8种优化构型.依据过渡态理论,从化学热力学和动力学方面对团簇Fe4 P的异构化反应进行研究,结果表明:二重态构型的稳定性最大且自旋多重度会影响团簇Fe4 P异构化转化的反应程度...     

Theoretical study on the reaction of N-(4-dehydrophenyi)pyridinium ion with nitroxides within the steric effects

应用量子化学密度泛函理论(DFT),在B3LYP/cc-pVDZ基组水平上,对N-(4-脱氢苯基)吡啶离子与不同结构的氮氧自由基反应进行了热动力学研究.优化了反应通道上反应物、中间体、过渡态和产物的几何构型并计算出它们的零点振动能( Ezpv)和焓值,分析数据研究位阻效应对反应的影响.研究表明3类氮氧自由基均与N-(4-脱氢苯基)吡啶离子自由基反应经过1个无位垒的放热过程生成1个中间体,然后发生自由基的重排,开环的氮氧自由基DTBN相较于闭合的氮氧自由基TMIO和TEMPO化学性质活泼、反应过程复杂.表明反应物本身的位阻效应为此类自由基反应的主要影响因素.     

Theoretical study of fullerene derivatives: C40H4 and C40X4 cluster molecules

Herein we demonstrate that the C₄₀ cluster molecule is easily formed to T_d symmetry structure and its ground state is ⁵A₂ open shell with four unpaired electrons. These four unpaired electrons are located at the tip points of the T_d symmetry structure. This work also indicates that these four unpaired electrons can easily react with a single valence atom, such as hydrogen or halogen atoms, to form a stable carbon hydrogen cluster molecule, C₄₀H₄, and carbon halogen cluster molecules, C₄₀X₄ (X=F, Cl, Br, I), respectively. The PM3 semiempirical molecular orbital method from Gaussian 94W computer program package was applied very well to these cluster molecules. According to the results in this study, the structures of geometrical optimization, ionization potential, energy gap, heat of formation, atomization energy, vibration frequency, and the remaining data of C₄₀H₄ and C₄₀X₄ cluster molecules. The above-calculated data prove that these unknown cluster molecules are stable and have a stable capacity similar to 1,3,5,7-tetrahaloadamantane molecules. They can be possibly synthesized experimentally in the near future. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 273–284, 1998     

位阻效应对N-(4-脱氢苯基)吡啶离子与氮氧自由基反应的理论计算研究

应用量子化学密度泛函理论(DFT),在B3LYP/cc-pVDZ基组水平上,对N-(4-脱氢苯基)吡啶离子与不同结构的氮氧自由基反应进行了热动力学研究.优化了反应通道上反应物、中间体、过渡态和产物的几何构型并计算出它们的零点振动能( Ezpv)和焓值,分析数据研究位阻效应对反应的影响.研究表明3类氮氧自由基均与N-(4...     

Theoretical study of fullerene derivatives: C28H4 and C28X4 cluster molecules

Based on the basic theory of C₂₈ cluster molecule proven by H. W. Kroto and the research findings of C₂₈'s derivative such as Ti@C₂₈* and Mg@C₂₈, proven by T. Guo, B. I. Dunlap, O. D. Haberlen, and others, we examine the two series fullerene derivatives, C₂₈H₄ and C₂₈X₄ cluster molecules, which are formed by the skeleton of C₂₈ cluster molecule. In this work, we not only prove that C₂₈ cluster molecule belongs to the T_d symmetry structure and its ground state is ⁵A₂ open-shell with four unpaired electrons, but also find that C₂₈ can easily react with single valence electron atoms, like hydrogen atom and halogen atoms, to be formed to stable fullerene derivatives, C₂₈H₄ and C₂₈X₄ cluster molecules (X=F, Cl, Br, I). The PM3 semiempirical molecular orbital method from G94W and Hyperchem program packages were applied very well in these fullerene derivatives. According to the results presented herein, we obtain the structures of geometrical optimization, ionization potential energy gap, heat of formation, atomization energy, and vibration frequency data of the C₂₈H₄ and C₂₈X₄ cluster molecules. The above calculation data confirm that these unknown fullerene derivatives are stable molecules; the stable behavior resembles the 1,3,5,7-tetrahaloadamantane molecules. It is quite possible that they can be synthesized experimentally in the near future. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 187–197, 1998     

Theoretical study on monometallic cyanide cluster fullerenes YCN@C72

The geometries, stabilities, and electronic properties of new endohedral fullerene YCN@C₇₂ have been investigated by the B3LYP and PBE1PBE density functional (DFT) methods. The C_2v(11188)‐C₇₂ cage, which violates the isolated pentagon rule (IPR) with a pair of fused pentagons, is predicted to be the lowest energy isomer for both empty and YCN@C₇₂. The relatively large HOMO‐LUMO gap (B3LYP: 1.48 eV, PBE1PBE: 1.68 eV) for YCN@C_2v(11188)‐C₇₂ reveals this structure kinetic stability. Significantly, the encased YCN cluster adopts a triangular structure inside the C_2v(11188)‐C₇₂ cage, similar to the results reported on YCN@C_s(6)‐C₈₂ and TbCN@C₂(5)‐C₈₂. Furthermore, the vertical ionization potential and electron affinity, UV‐vis‐NIR and IR spectra of YCN@C_2v(11188)‐C₇₂ have been predicted to facilitate future experimental characterization. © 2015 Wiley Periodicals, Inc.     

Simulation of water cluster assembly on a graphite surface

The assembly of small water clusters (H2O)n, n = 1-6, on a graphite surface is studied using a density functional tight-binding method complemented with an empirical van der Waals force correction, with confirmation using second-order M?ller-Plesset perturbation theory. It is shown that the optimized geometry of the water hexamer may change its original structure to an isoenergy one when interacting with a graphite surface in some specific orientation, while the smaller water cluster will maintain its cyclic or linear configurations (for the water dimer). The binding energy of water clusters interacting with graphite is dependent on the number of water molecules that form hydrogen bonds, but is independent of the water cluster size. These physically adsorbed water clusters show little change in their IR peak position and leave an almost perfect graphite surface.     

Theoretical study of the H(2) reaction with a Pt(4) (111) cluster

The C(s) symmetry reaction of the H(2) molecule on a Pt(4) (111) clusters, has been studied using ab initio multiconfiguration self-consistent field plus extensive multireference configuration interaction variational and perturbative calculations. The H(2) interaction by the vertex and by the base of a tetrahedral Pt(4) cluster were studied in ground and excited triplet and singlet states (closed and open shells), where the reaction curves are obtained through many avoided crossings. The Pt(4) cluster captures and activates the hydrogen molecule; it shows a similar behavior compared with other Pt(n) (n=1,2,3) systems. The Pt(4) cluster in their lowest five open and closed shell electronic states: (3)B(2), (1)B(2), (1)A(1) (3)A(1), (1)A(1), respectively, may capture and dissociate the H(2) molecule without activation barriers for the hydrogen molecule vertex approach. For the threefolded site reaction, i.e., by the base, the situation is different, the hydrogen adsorption presents some barriers. The potential energy minima occur outside and inside the cluster, with strong activation of the H-H bond. In all cases studied, the Pt(4) cluster does not absorb the hydrogen molecule.     

N-烯基硝酮分子内环加成反应区域选择性的理论研究IV. N-4-己烯基硝酮分子内环加成反应的区域选择性

本文用AM1 MO方法和过渡状态理论研究N-4-己烯基硝酮分子内环加成反应的机理, 计算两个平行反应(a, b)的速率常数的比值, 得到与实验吻合的结果。计算结果还表明, 由于N-5-甲基的电子效应, 使得反应b的活化焓降低, 同时, N-5-甲基引起的构型变化, 使得反应b的活化熵增高(绝对值变小), 这使得K~b/K~a值明显增长, 是区域选择性发生较大改变的原因。     

Photoelectron spectroscopy and Ab initio study of the structure and bonding of Al7N- and Al7N

The electronic and geometrical structures of Al7N- are investigated using photoelectron spectroscopy and ab initio calculations. Photoelectron spectra of Al7N- have been obtained at three photon energies with six resolved spectral features at 193 nm. The spectral features of Al7N- are relatively broad, in particular for the ground state transition, indicating a large geometrical change from the ground state of Al7N- to that of Al7N. The ground state vertical detachment energy is measured to be 2.71 eV, whereas only an upper limit of approximately 1.9 eV can be estimated for the ground state adiabatic detachment energy due to the broad detachment band. Global minimum searches for A7N- and Al7N are performed using several theoretical methods. Vertical electron detachment energies are calculated using three different methods for the lowest energy structure and compared with the experimental data. Calculated results are in excellent agreement with the experimental data. The global minimum structure of Al7N- is found to possess C3v symmetry, which can be viewed as an Al atom capping a face of a N-centered Al6N octahedron. In the ground state of Al7N, however, the capping Al atom is pushed inward with the three adjacent Al-Al distances being stretched outward. Thus, even though Al7N still possesses C3v symmetry, it is better viewed as a N-coordinated by seven Al atoms in a cage-like structure. The chemical bonding in Al7N- is discussed on the basis of molecular orbital and natural bond analysis.     

N-烯基硝酮分子内环加成反应区域选择性的理论研究 3:N-4-甲基-4-戊烯基硝酮分子内环加成反应的区域选择性

N-4-甲基-4-戊烯基硝酮分子内环加成反应可以生成氧桥型(Pa)和碳桥型(Pb)两种产物, 其实验产率比约为8:1。而在N-4位未取代的情况下, Pa与Pb的实验产率比约为1:2。可见N-4-甲基使得区域选择性发生了很大的变化。本文用AM1 MO方法和过渡状态理论研究了N-4-甲基-4-戊烯基硝酮分子内环加成反应的机理。计算了两个平行反应(a, b)的速率常数的比值, 得到与实验吻合的结果。计算表明, N-4-甲基取代后, a, b两反应的活化熵的相对变化是区域选择性改变的主要因素, 活化焓的相对变化只是一个次要因素。     

ChemInform Abstract: Theoretical Study on the Assembly and Stabilization of a Magic Cluster Al4N‐

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Theoretical study of cooperativity in multivalent polymers for colloidal stabilization

Multivalent polymers, i.e., copolymers with multiple binding sites, have been proposed recently for stabilization of fusogentic liposomes and other liposomal colloids useful for drug delivery. The performance of such polymers critically depends on their molecular architecture, in particular the strength and frequency of surface anchoring sites along the backbone of a highly soluble polymer. In this work, we investigate the adsorption and surface forces due to multivalent polymers based on coarse-grained polymer models. We find that for W-type polymers that form dangling tails when all anchoring segments are attached to a surface, increasing the chain length at fixed polymer composition leads to a stronger repulsive barrier in the polymer-mediated surface forces thereby increasing the ability of the polymer to stabilize colloidal particles. This prediction conforms to an earlier experiment indicating that increasing the number of hydrophobic anchors along poly(ethylene glycol) polymers results in the cooperative behavior for both surface adsorption and steric stabilization. For M-type multivalent polymers that have weakly anchoring sites placed at the ends, however, addition of binding sites at fixed polymer composition could lead to negative cooperativity, i.e., the more binding sites, the less the amount of adsorption or the weaker the ability of surface protection. The theory also predicts that polymers with two anchoring sites (e.g., telechelic copolymers) are most efficient for colloidal stabilization.     

Formation of the magic cluster Na8 in noble gas matrixes

The sodium molecules Na(2), Na(4), and Na(8) have been isolated in argon matrixes at 15 K and characterized for the first time by Raman spectroscopy. The vibrational frequencies are compared with density functional (DFT) calculations. The Na(4) cluster possesses a rhombic structure (D(2h)) with calculated d(Na-Na) = 307.2 and 347.4 pm, respectively. For octasodium, a hypertetrahedral structure (T(d)) is predicted in which each side of an inner tetrahedron with d(Na-Na) = 331.5 pm is capped by sodium atoms with a distance of d(Na-Na) = 348.7 pm. The green octasodium cluster is the first example of a matrix-isolated magic number cluster. Its formation from blue tetrasodium is discussed on the basis of the observed sequence of cluster growth.     

Configuration dependent critical nuclei in the self assembly of magic clusters

Evidence for the formation of various 2-D structures possessing different numbers of Co-Si magic clusters (size approximately 10.0 +/- 0.5 A), configurations and lifetimes are studied in real time on a Si(111)-(7 x 7) surface at elevated temperature in the STM. Observations of individual cluster diffusion, attachment and detachment dynamics resolve unequivocally the question of self assembly over surface reconstruction. The smallest stable structure consisting of seven individual Co-Si magic clusters arranged in a hexagonal closed packed formation (i = 7) is found to retain sufficient cohesive energy to avoid dissociation. A configuration dependent critical 2-D nuclei (i* = 6) is determined to exist in facilitating the self assembly dynamics.