Theoretical study on the structure and property relationship of the cationic conjugated polyelectrolytes

A theoretical study using density functional theory was performed to understand the structure/property relationship of the cationic conjugated polyelectrolytes, poly[9,9-bis-(6′-N,N,N-trimethylammonium) hexyl] fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT-X, where X = Br). The torsion angle between the fluorene and benzothiadiazole units in the PFBT monomer was found to substantially affect the structural and electronic properties of the cationic PFBT monomer. The changes of geometrical parameter, HOMO and LUMO energy levels, and band gap, as well as the absorption maximum are discussed in terms of the torsion in the PFBT monomer structure. For comparison, its neutral analogue, the monomer of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) was also studied. The length of conjugation backbone was also examined.     

合成气制乙醇的铑基催化剂中助剂铁,锂的作用本质研究

催化活性测试表明,助剂Fe具有显著提高乙醇生成选择性及铑催化活性的双重作用;助剂Li具有显著提高乙醇选择性的作用,对铑催化活性影响不大。基于H_2/D_2同位素效应结果及CO化学吸附、IR、XRD、XPS等的表征结果,认为助剂Fe经活化处理后大部分与Rh形成RhFe合金,使Rh分散度显著提高,从而提高了乙醇的选择性;Rh分散度的提高以及小部分以Fe~(2+)(Fe~(3+))形式存在的助剂Fe促进甲酰基的生成及随后的氢解断C-O键反应是助剂Fe促使铑催化活性提高的两个因素。Li的主要作用在于通过与C_2含氧中间体乙烯酮氧端的弱亲合作用,促进了乙醇前驱体的生成,从而使乙醇生成选择性提高。     

8-羟基喹啉单体及二聚体质子转移反应的理论研究

Density functional theory （DFT） of quantum chemistry method was employed to investigate proton transfer reactions of 8-hydroxyquinoline （8-HQ） monomers and dimers. By studying the potential energy curves of the isomerization, the most possible reaction pathway was found. The total energy of 8-hydroxyquinoline was lower than that of quinolin-8（1H）-one, whereas the order was reversed in dimers. The findings explained the contrary experimental phenomena. The minimum reaction barrier of intramolecular proton transfer was 47.3 kJ/mol while that in dimer was only 25.7 kJ/mol. Hence it is obvious that proton transfer reactions of 8-HQ monomer have a considerable rate but it is easier to proceed for 8-HQ dimer than monomers. It implied that the hydrogen bond played an important role in depressing the activation energy of reaction. The mechanism of the tautomerization was discussed on the basis of theoretical results.     

Oxidative addition of the ethane C-C bond to Pd. An ab initio benchmark and DFT validation study

We have computed a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the ethane C-C bond to the palladium atom and have used this to evaluate the performance of 24 popular density functionals, covering LDA, GGA, meta-GGA, and hybrid density functionals, for describing this reaction. The ab initio benchmark is obtained by exploring the PES using a hierarchical series of ab initio methods [HF, MP2, CCSD, CCSD(T)] in combination with a hierarchical series of five Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account either through a relativistic effective core potential for palladium or through a full four-component all-electron approach. Our best estimate of kinetic and thermodynamic parameters is -10.8 (-11.3) kcal/mol for the formation of the reactant complex, 19.4 (17.1) kcal/mol for the activation energy relative to the separate reactants, and -4.5 (-6.8) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). Our work highlights the importance of sufficient higher angular momentum polarization functions for correctly describing metal-d-electron correlation. Best overall agreement with our ab initio benchmark is obtained by functionals from all three categories, GGA, meta-GGA, and hybrid DFT, with mean absolute errors of 1.5 to 2.5 kcal/mol and errors in activation energies ranging from -0.2 to -3.2 kcal/mol. Interestingly, the well-known BLYP functional compares very reasonably with a slight underestimation of the overall barrier by -0.9 kcal/mol. For comparison, with B3LYP we arrive at an overestimation of the overall barrier by 5.8 kcal/mol. On the other hand, B3LYP performs excellently for the central barrier (i.e., relative to the reactant complex) which it underestimates by only -0.1 kcal/mol.     

Characterization of the monovalent ion position and hydrogen-bond network in guanine quartets by DFT calculations of NMR parameters

Conformational stability of G-quartets found in telomeric DNA quadruplex structures requires the coordination of monovalent ions. Here, an extensive Hartree-Fock and density functional theory analysis of the energetically favored position of Li+, Na+, and K+ ions is presented. The calculations show that at quartet-quartet distances observed in DNA quadruplex structures (3.3 A), the Li+ and Na+ ions favor positions of 0.55 and 0.95 A outside the plane of the G-quartet, respectively. The larger K+ ion prefers a central position between successive G-quartets. The energy barrier separating the minima in the quartet-ion-quartet model are much smaller for the Li+ and Na+ ions compared with the K+ ion; this suggests that K+ ions will not move as freely through the central channel of the DNA quadruplex. Spin-spin coupling constants and isotropic chemical shifts in G-quartets extracted from crystal structures of K+- and Na+-coordinated DNA quadruplexes were calculated with B3LYP/6-311G(d). The results show that the sizes of the trans-hydrogen-bond couplings are influenced primarily by the hydrogen bond geometry and only slightly by the presence of the ion. The calculations show that the R(N2N7) distance of the N2-H2...N7 hydrogen bond is characterized by strong correlations to both the chemical shifts of the donor group atoms and the (h2)J(N2N7) couplings. In contrast, weaker correlations between the (h3)J(N1C6') couplings and single geometric factors related to the N1-H1...O6=C6 hydrogen bond are observed. As such, deriving geometric information on the hydrogen bond through the use of trans-hydrogen-bond couplings and chemical shifts is more complex for the N1-H1...O6=C6 hydrogen bond than for the N2-H2...N7 moiety. The computed trans-hydrogen-bond couplings are shown to correlate with the experimentally determined couplings. However, the experimental values do not show such strong geometric dependencies.     

Synthesis, structure, and dynamics of six-membered metallacoronands and metallodendrimers of iron and indium

In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) (1)H NMR spectroscopy for the indium wheel [In(6)Cl(6)(L(1))(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre [ 1/6[S(6)-5]<==>[1/6[S(6)-5']]. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers.     

Adsorption of organic substances on broken clay surfaces: a quantum chemical study

Hydrogen-bonded interactions between local defect structures on broken clay surfaces modeled as molecular clusters and the organic molecules acetic acid, acetate, and N-methylacetamide (NMA) have been investigated. Density functional theory and polarized basis sets have been used for the computation of optimized interaction complexes and formation energies. The activity of the defect structures has been characterized as physical or chemical in terms of the strength of the hydrogen bonds formed. Chemical defects lead to significantly enhanced interactions with stronger hydrogen bonds and larger elongation of OH bonds in comparison to the physical defects. The type of interaction with the defect structure significantly influences the planarity of the model peptide bond in NMA. Both cases, enhancement of the planarity by increase of the CN double bond character and strong deviations from planarity, are observed.     

呋喃-乙酸分子间相互作用的量子化学研究

用密度泛函理论B3LYP方法选取6-311＋＋G(d,p)基组对呋喃-乙酸复合物进行了量子化学计算研究, 通过在相同水平下的频率振动分析发现了该势能面上6个极小值点, 其最稳定构型对应一强O…H—O型氢键, 其结合能在消除基组重叠误差后为－20.87 kJ•mol^－1. 通过自然键轨道(NBO)分析, 研究了电荷转移及轨道相互作用. 通过自洽反应场(SCRF)理论中的Onsager 溶剂模型在介电常数分别为1.0, 2.247, 4.9, 7.58, 10.36, 20.7, 32.63, 38.2, 46.7, 78.39的不同溶剂环境下重新优化呋喃与乙酸势能面上最稳定构型A, 研究了溶剂对呋喃-乙酸复合物几何构型、电荷分布、偶极矩以及结合能的影响. 发现溶剂化作用增大了呋喃与乙酸分子间的结合能, 导致O…H距离减小, H—O振动频率红移. 当溶液介电常数在1.0～32.63范围时, 溶剂效应十分显著, 当介电常数大于32.63后, 溶剂化作用几乎达到了极限.     

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten-triiridium clusters

Reaction of WH(CO)₃(η-C₅Me₅) with IrCl(CO)₂(4-H₂NC₆H₄Me) affords WIr₃(μ-CO)₃(CO)₈(η-C₅Me₅) in low yield. A structural study reveals a WIr₂-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr₃(CO)₁₁(η-C₅H₅) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr₃(CO)₁₁(η-C₅H₅) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. ¹³C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr₃(CO)₁₁(η-C₅H₅) and the related tetrahedral cluster W₂Ir₂(CO)₁₀(η-C₅H₅)₂ are very fast and involve all carbonyls on the clusters. DFT calculations on MIr₃(CO)₁₁(η-C₅H₅) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener.     

Nonlinear Optical Properties of Tri—nuclear Transition Metal Clusters M—（μ—S）s—M′（M=Mo,W;M′=Cu,Ag,Au）

The static polarizabilities and the second-order hyperpolarizabilities of a series of tri-nuclear metal cluster models MS4(M′PPh3)2(M′PPh3)(M=Mo,W;M′=Cu,Ag,Au)have been calculated within the first-principle theoretical framework. The model clusters have two fragments of rhombic units and it is the charge ransfer from one of these moieties to the other that is responsible for nonlinear optical property. This kind of electronic delocaization, differentiated from that of planar π-system, is very interesting and is worthy for further investigation.