Ab initio study on the hydrogen desorption from MH-NH3 (M = Li, Na, K) hydrogen storage systems

The hydrogen storage system LiH + NH(3) ? LiNH(2) + H(2) is one of the most promising hydrogen storage systems, where the reaction yield can be increased by replacing Li in LiH with other alkali metals (Na or K) in order of Li < Na < K. In this paper, we have studied the alkali metal M (M = Li, Na, K) dependence of the reactivity of MH with NH(3) by calculating the potential barrier of the H(2) desorption process from the reaction of an M(2)H(2) cluster with an NH(3) molecule based on the ab initio structure optimization method. We have shown that the height of the potential barrier becomes lower in order of Li, Na, and K, where the difference of the potential barrier in Li and Na is relatively smaller than that in Na and K, and this tendency is consistent with the recent experimental results. We have also shown that the H-H distance of the H(2) dimer at the transition state takes larger distance and the change of the potential energy around the transition state becomes softer in order of Li, Na, and K. There are almost no M dependence in the charge of the H atom in NH(3) before the reaction, while that of the H atom in M(2)H(2) takes larger negative value in order of Li, Na, and K. We have also performed molecular dynamics simulations on the M(2)H(2)-NH(3) system and succeeded to reproduce the H(2) desorption from the reaction of Na(2)H(2) with NH(3).     

MAlH4(M=Li,Na)储氢材料*

氢能是一种新型的清洁能源,有望替代碳经济,而氢的储存是氢能应用的关键。近年来,研究集中在具有储氢容量高和可逆性好等优点的固态储氢材料上。许多新型储氢材料不断出现,其中以MAlH₄(M=Li, Na)为代表的金属复合氢化物体系被认为是最有前景的储氢材料之一。本文综述了MAlH₄(M=Li, Na)作为可逆储氢材料的研究现状,主要从吸放氢反应、储氢性能、反应机理、理论计算和存在的问题等方面进行了讨论,并指出其相关发展趋势。     

Les systemes binaires AlPO4−M3PO4 (M=Li,Na, K)

The liquid-solid phase diagram of the binary systems AlPO₄?M₃PO₄(M=Li, Na, K) have been established. The additional compounds Na₃Al(PO₄)₂, Na₃Al₂(PO₄)₃ and K₃Al₂(PO₄)₃ have been found again. A new compound K₃Al(PO₄)₂ is observed. The melting point of Na₃PO₄ is 1545°C and K₃PO₄ does not melt up to 1700°C.     

高能密度材料H2N5MN5H2 (M=Be,Mg,Ca,Zn,和Cd)的密度泛函理论研究

借助密度泛函理论,用B3LYP和BP86方法,对一系列潜在的新型高能密度材料分子H2N5MN5H2(M=Be,Mg,Ca,Zn,和Cd)进行了理论预测研究.结果表明,这些材料分子都非常稳定,不容易分解,其中H2N5BeN5H2最稳定.金属离子的配位作用对化合物的稳定起了重要作用.配体H2N5也因从金属M获得一个电子变成H2N5-离子而变得更稳定.     

Octacoordination of the nitrogen atom in M4NO 4 + systems (M = Li, Na, K)

The electronic and geometric structures of M₄NO ₄ ⁺ compounds (M = Li, Na, K) in classical and nonclassical isomeric forms were studied by the ab initio (MP2(full)/6-311+G**) and density functional theory (B3LYP/6-311+G**) methods. For all M atoms, structurally stable nonclassical isomers were found with octacoordinated nitrogen atoms and tetracoordinated oxygen atoms. For Li₄NO ₄ ⁺ , the classical structure with the tetracoordinated nitrogen atom is energetically more stable, whereas nonclassical structures with the octacoordinated nitrogen center are more stable for Na₄NO ₄ ⁺ and K₄NO ₄ ⁺ .     

不饱和类硅烯H2C＝SiMBr (M＝Li, Na)的DFT研究

采用密度泛函理论方法, 在B3LYP/6-311G (d,p)水平上研究了不饱和类硅烯H₂C＝SiMBr (M＝Li, Na)的结构. 结果表明, 不饱和类硅烯H₂C＝SiLiBr与H₂C＝SiNaBr各有三种平衡构型, 其中非平面的p-配合物型构型能量最低, 是这两种不饱和类硅烯存在的主要构型. 对平衡构型间异构化反应的过渡态进行了计算, 求得了转化势垒. 计算预言了最稳定构型的振动频率和红外强度.     

溴代类卡宾H2CMBr(M=Na,K)的结构与稳定性

本文用RHF/3-21G^*解析梯度方法研究了溴代类卡宾H2CMBr(M=Na,K)势能面的主要特征, 得到了它们各自的三种平衡构型及两种异构化的过渡态构型, 并用二级微扰方法进行了能量的相关能校正, 计算了振动频率, 以确证平衡构型和过渡态。计算结果表明, 溴代类卡宾H2CMBr(M=N,K))的三元环构型是最稳定的几何构型, 其它的两种构型σ-配合物和p-配合物, 也是势能面上的极值点, 但能量相对较高, 不稳定。本文分析了各构型的特点, 对其化学反应特性进行了评估。     

Insights from impedance spectroscopy into the mechanism of thermal decomposition of M(NH2BH3), M = H, Li, Na, Li(0.5)Na(0.5), hydrogen stores

We report the first solid-state impedance study of hydrogen-rich ammonia borane, AB, and its three alkali metal amidoborane derivatives. Temperature-dependent impedance spectra of solid M(NH(2)BH(3)) salts are predominated by ionic conductivity, which at room temperature ranges from 5.5 μS cm(-1) (M = Li) to 2.2-3.0 mS cm(-1) (Na, Na(0.5)Li(0.5)), while the activation energy for conductivity is rather high (140-158 kJ mol(-1)). Variation of conductivity with time can be used to extract information about the evolution of the system during thermal decomposition. By using a combination of impedance spectroscopy, thermogravimetric analysis, scanning calorimetry, evolved gas analysis, infrared absorption spectroscopy as well as (11)B and (1)H MAS NMR, we were able to reconfirm the complex pathway of thermal decomposition of amidoboranes postulated by two of us earlier (J. Mater. Chem. 2009, 19, 2043).     

Interactions of peptides with metallic cations. I. Complexes glycylglycine–M (M=Li, Na)

In view of better understanding interactions of aminoacids and peptides with metallic cations, in the isolated state and in water, the model system glycylglycine–M⁺ (M=Li, Na) has been studied theoretically. The computations have been performed with the help of the density functional theory (DFT) and the B3LYP functional. The extended basis set was the standard 6-31++G**. In solution we used a recent model of continuum with a multicentric multipole expansion of the charge distribution. Our study shows that low energy complexes with lithium and sodium are rather similar. In the isolated state, the most stable form corresponds to a bidentate complex in which the cation interacts with two oxygen atoms, one from the terminal COOH and one from the amidic carbonyl. In solution, the coordination of the cation in the most stable form is 3, the nitrogen of the end amino group being the third ligand.

The energy range between the lowest energy structure and the highest energy one, in both cases, is slightly reduced under the electrostatic influence of the solvent.     

Theoretical studies of group 1 metal complexes with hydrogen fluoride, M(HF)n, M = Li, Na, and K: a new type of electrides

Small clusters of group 1 metal complexes with hydrogen fluoride molecules M(HF)n, M = Li, Na, and K, are studied with the ab initio molecular orbital method. The trimer M(HF)3 forms a C3v cluster, in which the metal atom is ionized and the ejected electron is trapped on the top of three equivalent HF molecules. The optimized geometric structure of Li(HF)3 is almost identical with that of the ion pair Li+(HF)3Cl- by replacing a Cl- anion with an ejected electron {e-}; thus Li(HF)3 can be described as Li+(HF)3{e-}. The entity {e-} is trapped under the electrostatic field created by three HF bond dipoles; and at the same time, the HF bonds are polarized and weakened. A triplet anion {e-}(HF)3Li+(HF)3{e-} is stable and is a possible anion unit of electrides.     

Die Systeme des Typs MCl/AlCl3/SO2 (M = Li,Na, K,NH4)

The MCl/AlCl₃/SO₂ Systems (M = Li, Na, K, NH₄) Phase diagrams of the ternary systems of the type MCl/AlCl₃/SO₂ were determined by measurement of SO₂ pressure, solubilities, and by thermal analysis. The complete phase diagram in the range from ?30 to +50°C is given for the case M = Na, partial diagrams for M = Li, K, NH₄. There exist solid compounds of the type MAlCl₄ · nSO₂ (M = Li, Na; n = 1.5 and 3) (M = K; n = 1.5 and 5) (M = NH₄; n = 5). Liquid phases can be obtained at room temperature and atmospheric pressure in the NaCl or LiCl containing systems.     

Imidazolidene carboxylate bound MBPh4 complexes (M = Li, Na) and their relevance in transcarboxylation reactions

Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO(2)) with the Lewis acids MBPh(4), where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh(4) yielded a dimeric species, yet coordination of IPrCO(2) with LiBPh(4) yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO(2)) with LiBPh(4) also afforded a dimeric species that was similar in global structure to that of the IPrCO(2)+NaBPh(4) dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO(2) (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO(2) to acetophenone with NaBPh(4) to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO(2) and acetophenone, whereas zero -order dependence was observed for NaBPh(4). Direct dicarboxylation was observed when I(t)BuCO(2) was added to MeCN in the absence of added MBPh(4).     

Synthesis, structure, and multi-NMR studies of (Me4N)[A(M(SC(O)Ph)3)2] (A = Na, M = Hg; A = K, M = Cd or Hg)

The compounds (Me4N)[A(M(SC(O)Ph)3)2] (A = K, M = Cd (2); A = Na, M = Hg (3); and A = K, M = Hg (4)) were synthesized by reacting the appropriate metal chloride with A+PhC(O)S- and Me4NCl in the ratios 1:3:1 and 2:6:1. The structures of these compounds were determined by single-crystal X-ray diffraction methods. All the compounds are isomorphous, isostructural, and crystallized in the space group P1 with Z = 1. Single-crystal data for 2: a = 106670(2) A, b = 111522(2) A, c = 119294(2) A, alpha = 71782(1) degrees, beta = 85208(1) degrees, gamma = 69418(1) degrees, V = 126140(4) A3, Dcalc = 1528 g cm-3. Single-crystal data for 3: a = 10840(2) A, b = 10946(4) A, c = 12006(3) A, alpha = 7218(2) degrees, beta = 8675(2) degrees, gamma = 6743(2) degrees, V = 12493(6) A3, Dcalc = 1756 g cm-3. Single-crystal data for 4: a = 104780(1) A, b = 112563(2) A, c = 119827(2) A, alpha = 71574(1) degrees, beta = 85084(1) degrees, gamma = 70705(1) degrees, V = 126523(3) A3, Dcalc = 1755 g cm-3. In the [A(M(SC(O)Ph)3)2]- anions, each M(II) atom is bonded to three thiobenzoate ligands through sulfur atoms, giving a trigonal planar MS3 geometry. The carbonyl oxygen atoms from the two [M(SC(O)Ph)3]- anions are bonded to the alkali metal atom, providing an octahedral environment. Solution metal NMR studies showed the concentration-dependent dissociation of the alkali metal ions in the trinuclear anions.     

Alkali metal salts of acrylamide C3H4NOM (M = Li,Na, and K): Synthesis and vibrational spectra

Alkali metal salts of acrylamide C₃H₄NOM (M = Li, Na, and K) were synthesized for the first time by metallation of acrylamide with alkali metals, their alkyl derivatives, or hydrides. The structures of the compounds synthesized were studied by Raman and IR spectroscopy. Based on the results obtained, an ionic structure was proposed for the salts. The salts were tested as initiators of the anionic polymerization of acrylamide. The catalytic activity of C₃H₄NOM in the polymerization of acrylamide is not lower than that of the well known catalyst, KOBu¹.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2316–2319, September, 1996.     

Rules on pair electron correlation in MOH (M=H,Li, Na)

In this article, the transferable property of pair correlation energies of OH components is discussed for a series of OH containing compounds MOH (M=H, Li, Na). In this series of compounds, from OH free radicals through HOH, LiOH, NaOH to OH^?, both the intra‐ and interpair correlation energies and intra‐ and intershell correlation energies of the inner orbital electrons change little. The 1s$_{\mathrm{O}}^{2}$ is very much alike in all the above OH containing systems and such a pair correlation is transferable. But the interpair correlation and intrashell correlation energies of the valence electrons are large and change a lot in all systems. In MOH molecules, the OH correlation energy contribution increases with the increase of the ionic bond strength of the compound and this contribution is always between the correlation energy values of OH free radicals and OH^? atomic groups. For strong ionic compounds, we present a very simple method to estimate the correlation energy by adding the correlation energies of its component ions within the chemical accuracy (2 kcal/mol). © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 311–317, 2001     

Alkali-metal trifluoromonosulphatomanganates (III) A2[MnF3(SO4)] (A = NH4, Li,Na or K)

Pink-brown crystalline alkali-metal trifluoromonosulphatomanganates(III), A₂[MnF₃(SO₄)] (A = NH₄, Li, Na or K), have been synthesised in high yields by reacting KMnO₄ or MnO(OH) with 40% HF and A₂SO₄ or by the reaction of MnO(OH) with 40% HF and A₂S₂O₈ (A = NH₄ or K). The chemicallly estimated oxidation state of manganese occurs between 2.9 and 3.1, and the room temperature magnetic moments lie in the range 4.0–4.2 BM. (NH₄)₂[MnF₃(SO₄)] on being pyrolysed at 340°C yields MnSO₄.