A cluster expansion theory with multireference functions using the unitary ansatz

A cluster expansion theory with multireference functions is developed. The method is applied to the ground state of H₂, the lowest two ¹∑⁺ states of LiH, and the lowest three ¹A₁ states of H₂O. Well-balanced potential curves are obtained for H₂ and LiH. Excitation energies are in good agreement with experiment.     

The B–C and C–C bonds as preferred electron source for H-bond and Li-bond interactions in complex pairing of C<Subscript>4</Subscript>B<Subscript>2</Subscript>H<Subscript>6</Subscript> with HF and LiH molecules

Ab initio calculations were used to analyze the interaction of C₄B₂H₆ with HF and LiH molecules at the mp2/6-311++g(2d,2p) computational level. Interaction of C₄B₂H₆ with HF results to H–F···H–C and C–B···H–F, C–C···H–F hydrogen bond as well as B–H···H–F dihydrogen bond complexes. Also interaction of C₄B₂H₆ with LiH results to B–C···LiH, C–C···LiH and B–H···LiH lithium bond as well as C–H···H–Li dihydrogen complexes. In the both cases, complexes involving interaction of HF or LiH with peripheral B–C and C–C bonds of the C₄B₂H₆ backbone have greater stabilities. The structures of complexes have been analyzed using AIM and NBO methodologies.     

Synergetic Effects of In Situ Formed CaH2 and LiBH4 on Hydrogen Storage Properties of the Li–Mg–N–H System

Hydrogen storage properties and mechanisms of the Ca(BH₄)₂‐doped Mg(NH₂)₂–2 LiH system are systematically investigated. It is found that a metathesis reaction between Ca(BH₄)₂ and LiH readily occurs to yield CaH₂ and LiBH₄ during ball milling. The Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite exhibits optimal hydrogen storage properties as it can reversibly store more than 4.5 wt % of H₂ with an onset temperature of about 90 °C for dehydrogenation and 60 °C for rehydrogenation. Isothermal measurements show that approximately 4.0 wt % of H₂ is rapidly desorbed from the Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite within 100 minutes at 140 °C, and rehydrogenation can be completed within 140 minutes at 105 °C and 100 bar H₂. In comparison with the pristine sample, the apparent activation energy and the reaction enthalpy change for dehydrogenation of the Mg(NH₂)₂–2 LiH–0.1 Ca(BH₄)₂ composite are decreased by about 16.5 % and 28.1 %, respectively, and thus are responsible for the lower operating temperature and the faster dehydrogenation/hydrogenation kinetics. The fact that the hydrogen storage performances of the Ca(BH₄)₂‐doped sample are superior to the individually CaH₂‐ or LiBH₄‐doped samples suggests that the in situ formed CaH₂ and LiBH₄ provide a synergetic effect on improving the hydrogen storage properties of the Mg(NH₂)₂–2 LiH system.     

二聚体C2H4-nFn···LiH (n=0, 1, 2)中π锂键的性质和弱方向性

采用二级微扰理论(MP2)量子化学研究方法, 对C₂H_4-nF_n···LiH (n=0, 1, 2)二聚体的结构和π锂键性质进行了分析. 结果表明氟原子的取代改变了乙烯分子的π电子云形状, 从而使二聚体体系中的π锂键发生偏移、伸长和弯曲. 通过与类似的π氢键体系C₂H_4-nF_n···HF (n=0, 1, 2)比较, 发现π锂键在二级弱相互作用的影响下, 发生了明显的弯曲, 表现出弱的方向性. 在CCSD(T)/6-311++G(3df, 3pd)理论水平下, 二聚体的相互作用能强弱顺序为: 33.85 kJ·mol^-1 (C₂H₄-LiH)>27.32 kJ·mol^-1 (C₂H₃F-LiH)>21.34 kJ·mol^-1 (cis-C₂H₂F₂-LiH)>20.25 kJ·mol^-1 (g-C₂H₂F₂-LiH), 说明氟取代削减了乙烯分子与LiH之间的相互作用.     

Assessing the Brønsted Basicity of Diaminoboryl Anions: Reactivity toward Methylated Benzenes and Dihydrogen

Treatment of toluene or p‐xylene with diaminoboryllithium results in consecutive reactions, involving boryl‐anion‐mediated deprotonation at the benzylic position followed by nucleophilic substitution at the boron center, producing benzylborane species and LiH. Diaminoboryllithium also cleaves H₂ heterolytically affording diaminohydroborane and LiH, while the reaction of lithium diaminoboryl(bromo)cuprate with H₂ takes place accompanied by reduction of Cu^I to give diaminohydroborane, LiH, and Cu⁰.     

Intermolecular complexes of nido-C<Subscript>2</Subscript>B<Subscript>3</Subscript>H<Subscript>7</Subscript> with HF and LiH molecules: the theoretical studies,bonding properties and natural bond orbital (NBO) analysis

The changes in stabilization energy upon the formation of intermolecular hydrogen, dihydrogen and lithium bond complexes between C₂B₃H₇, LiH and HF have been investigated using MP2 method with aug-cc-pVDZ basis set. The interaction of HF with nido-C₂B₃H₇ could occur through the formation of B–H^?δ···^+δH–F, C–H^+δ···F^?δ–H and B–C···H–F classical and non-classical hydrogen bonds. The B–C bonds in backbone of the C₂B₃H₇ as electron donor interact with σ* orbital of HF as electron acceptor. Also interaction of LiH with nido-C₂B₃H₇ resulted in B–C···Li–H and B–H···LiH lithium bonds as well as C–H···H–Li dihydrogen bond complexes. In some of these complexes, LiH interacts with B–C bonds. Results are indicating that more stable complexes belong to interaction of HF and LiH with backbone of the nido-C₂B₃H₇. The AIM and NBO methods were used to analyze the intermolecular interactions; also the electron density at the bond critical point and the charge transfer of obtained complexes were studied.     

The influence of electron correlation on reaction energies. The dimerization energies of BH3 and LiH

Results of rigorous computations employing extended Gaussian-type basis sets are reported for BH₃, B₂H₆, LiH, and Li₂H₂ in their respective equilibrium geometries. The dimerization energy of BH₃ is calculated as −20.7 kcal/mol within the Hartree-Fock approximation and as −36.6 kcal/mol if electron correlation is included. The corresponding results for the dimerization of LiH are −47.3 kcal/mol and −48.3 kcal/mol. Partitioning of the correlation energy contributions allows to attribute the effect of electron correlation to the increase of next neighbour bond interactions on the dimerization of BH₃ and LiH. The difficulties of accurate computations of reaction energies are discussed in detail.     

Analytical energy surfaces for the collinear H+H2 and Li+H2 exchange reactions

A simple four-parameter function is shown to possess adequate flexibility to fit the H + H₂ →H₂ + H and Li + H₂ → LiH + H exchange reaction energy surfaces to good accuracy along the reaction paths.     

Effects of Stoichiometry on the H2‐Storage Properties of Mg(NH2)2–LiH–LiBH4 Tri‐Component Systems

The hydrogen desorption pathways and storage properties of 2 Mg(NH₂)₂–3 LiH–x LiBH₄ samples (x =0, 1, 2, and 4) were investigated systematically by a combination of pressure composition isotherm (PCI), differential scanning calorimetric (DSC), and volumetric release methods. Experimental results showed that the desorption peak temperatures of 2 Mg(NH₂)₂–3 LiH–x LiBH₄ samples were approximately 10–15 °C lower than that of 2 Mg(NH₂)₂–3 LiH. The 2 Mg(NH₂)₂–3 LiH–4 LiBH₄ composite in particular began to release hydrogen at 90 °C, thereby exhibiting superior dehydrogenation performance. All of the LiBH₄‐doped samples could be fully dehydrogenated and re‐hydrogenated at a temperature of 143 °C. The high hydrogen pressure region (above 50 bar) of PCI curves for the LiBH₄‐doped samples rose as the amount of LiBH₄ increased. LiBH₄ changed the desorption pathway of the 2 Mg(NH₂)₂–3 LiH sample under a hydrogen pressure of 50 bar, thereby resulting in the formation of MgNH and molten [LiNH₂–2 LiBH₄]. That is different from the dehydrogenation pathway of 2 Mg(NH₂)₂–3 LiH sample without LiBH₄, which formed Li₂Mg₂N₃H₃ and LiNH₂, as reported previously. In addition, the results of DSC analyses showed that the doped samples exhibited two independent endothermic events, which might be related to two different desorption pathways.     

Three‐Component Reaction of an Isocyanide and a Dialkyl Acetylenedicarboxylate with a Phenacyl Halide in the Presence of Water: An Efficient Method for the One‐Pot Synthesis of γ‐Iminolactone Derivatives

The zwitterion, formed from the reaction of an alkyl isocyanide and a dialkyl acetylenedicarboxylate, reacts with phenacyl halides in H₂O to produce γ‐iminolactone derivatives in high yields. H₂O helps to avoid the use of highly toxic and environmentally unfavorable solvents for this conversion.     

Static charge distributions which generate exact potential curves for diatomic molecules

For a diatomic molecule, there exists a charge density which can be used to generate the exact potential energy curve for the molecule, by integration of the classical Poisson equation. This density is displayed for H⁺₂, H₂ and LiH, and it is shown to be similar in shape to the united-atom electron density.     

Peroxidase-like activity of cytochrome c in the presence of anionic surfactants

Peroxidase-like activity of cytochrome c is significantly higher in the presence of anionic surfactants, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium n-dodecyl sulphate (SDS). The enhancement is due to the higher reaction rate of the cytochrome c with H₂O₂, which is the rate determining step in the peroxidase cycle of cytochrome c. An intermediate formed in the cycle rapidly oxidizes the substrates or reacts with further molecule(s) of H₂O₂, causing heme degradation. Thus, the specific microenvironment provided by anionic surfactants facilitates also degradation of heme iron by H₂O₂.     

Investigations on the solid state interaction between LiAlH4 and NaNH2

In this paper, two LiAlH₄-NaNH₂ samples with LiAlH₄ to NaNH₂ molar ratio of 1/2 and 2/1 were investigated, respectively. It was observed that both samples evolved 2 equiv H₂ in the ball milling process, however, the reaction pathways were different. For the LiAlH₄-NaNH₂ (1/2) sample, Li₃Na(NH₂)₄ and NaAlH₄ were formed through cation exchange between reactants. The NaAlH₄ formed further reacts with Li₃Na(NH₂)₄ and NaNH₂ to give H₂, NaH and LiAlN₂H₂. For the LiAlH₄-NaNH₂ (2/1) sample, Li₃Na(NH₂)₄, LiNH₂ and NaAlH₄ were formed firstly through the same cation exchange process. The resulting LiNH₂ reacts with the remaining LiAlH₄ and produces H₂ and Li₂AlNH₂.     

The use of biorthogonal sets in valence bond calculations

The “non-orthogonality problem” in valence bond theory is avoided by using two sets of basis functions, with a biorthogonality property, together with the method of moments. The basis set limit is reached whenall structures are included, but even truncated sets give good (though not monotonic) convergence. Calculations are reported for H₂, LiH, and H₂O.     

Lithiated Primary Amine—A New Material for Hydrogen Storage

A facile method for synthesizing crystalline lithiated amines by ball milling primary amines with LiH was developed. The lithiated amines exhibit an unprecedented endothermic dehydrogenation feature in the temperature range of 150–250 °C, which shows potential as a new type of hydrogen storage material. Structural analysis and mechanistic studies on lithiated ethylenediamine (Li₂EDA) indicates that Li may mediate the dehydrogenation through an α,β‐LiH elimination mechanism, creating a more energy favorable pathway for the selective H₂ release.     

Reaction of 2-vinylfuran with formaldehyde catalyzed by palladium complexes

Conclusion 5-Hydroxymethyl-2-vinylfuran is formed when 2-vinylfuran reacts with formaldehyde in the presence of Pd(acac)₂-PPh₃-Al(C₂H₅)₃ catalyst (1:3:4) in a 70% yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 693–695, March, 1976.     

Reactions of homobinuclear platinum and palladium complexes with carbon monoxide

The reactivity of homobimetallic complexes of platinum(II) and palladium(II) containing diethyl(diphenylphosphinomethyl)amine (ddpa = (C₆H₅)₂PCH₂N(C₂H₅)₂) as a bridging ligand has been investigated. Carbon monoxide reacts reversibly with these complexes. The species formed are binuclear carbonyl-bridged derivatives, which can isomerize to ionic terminal carbonyl complexes. Reaction of [PtCl₂(CO)]₂[(C₂H₅)₄N]₂ with ddpa in dichloromethane gives the ionic platinum(I) complex [Pt(ddpa)Cl₂]₂[(C₂H₅)₄N]₂, which reacts with carbon monoxide. Still, homobimetallic derivatives of palladium(I) are unstable, and none have been isolated.     

Orientation of endohedral H2, CO,and LiH inside heptagon‐containing C58 and C58H18

Three H₂@C₅₈H_x, six CO@C₅₈H_x, and six LiH@C₅₈H_x (x = 0 and 18) complexes were optimized using B3LYP/6‐31G* method. The results show that both C₅₈ and C₅₈H₁₈ destabilize nonpolar H₂ and weakly polar CO, and stabilize strongly polar LiH inside their cages. Three H₂@C₅₈H_x (x = 0 and 18) complexes are nearly equivalent in energy, and CO orients the longest direction of cage because of spatial repulsion between them in the most stable CO@C₅₈H_x (x = 0 and 18) isomers. Orientation of LiH inside C₅₈H_x (x = 0 and 18) cages is determined by dipole‐induced dipole attractive interaction between them, and this attraction is especially significant in LiH@C₅₈H₁₈ complexes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

The first synthesis of 8-aza-2-polyfluoroalkylchromones

The condensation of 3-acetyl-4,6-dimethyl-2-pyridone with R_FCO₂Et in the presence of LiH in dioxane affords corresponding R_F-containing β-diketones, whose dehydration under the action of conc. H₂SO₄ gives 8-aza-5,7-dimethyl-2-polyfluoroalkylchromones.