Assessment of intermolecular interactions at three sites of the arylalkyne in phenylacetylene‐containing lithium‐bonded complexes: Ab initio and QTAIM studies

The intermolecular interactions existing at three different sites between phenylacetylene and LiX (X = OH, NH₂, F, Cl, Br, CN, NC) have been investigated by means of second‐order Møller?Plesset perturbation theory (MP2) calculations and quantum theory of “atoms in molecules” (QTAIM) studies. At each site, the lithium‐bonding interactions with electron‐withdrawing groups (? F, ? Cl, ? Br, ? CN, ? NC) were found to be stronger than those with electron‐donating groups (? OH and ? NH₂). Molecular graphs of C₆H₅C?CH···LiF and πC₆H₅C?CH···LiF show the same connectional positions, and the electron densities at the lithium bond critical points (BCPs) of the πC₆H₅C?CH···LiF complexes are distinctly higher than those of the σC₆H₅C?CH···LiF complexes, indicating that the intermolecular interactions in the C₆H₅C?CH···LiX complexes can be mainly attributed to the π‐type interaction. QTAIM studies have shown that these lithium‐bond interactions display the characteristics of “closed‐shell” noncovalent interactions, and the molecular formation density difference indicates that electron transfer plays an important role in the formation of the lithium bond. For each site, linear relationships have been found between the topological properties at the BCP (the electron density ρ_b, its Laplacian ?²ρ_b, and the eigenvalue λ₃ of the Hessian matrix) and the lithium bond length d(Li‐bond). The shorter the lithium bond length d(Li‐bond), the larger ρ_b, and the stronger the π···Li bond. The shorter d(Li‐bond), the larger ?²ρ_b, and the greater the electrostatic character of the π···Li bond. © 2012 Wiley Periodicals, Inc.     

乙烯、乙炔和苯与氨基锂间的π型锂键相互作用

分别在DFT-B3LYP和MP2/6-311++G**水平上求得乙烯、乙炔和苯与氨基锂锂键复合物势能面上的3个几何构型. 频率分析表明,3个构型均为稳定构型. 计算结果表明,形成锂键复合物后,质子供体N(2)- Li(4)的键长明显增大,且其伸缩振动的频率发生了不同程度的红移. 分别在乙烯…氨基锂、乙炔…氨基锂和苯…氨基锂三种复合物中,经MP2/6-311++G**水平计算的同时含基组重叠误差(BSSE)和零点振动能校正的单体间锂键相互作用能分别为-26.04、-24.86 和 -30.02 kJ·mol-1. 自然键轨道理论（NBO）分析表明单体间的弱相互作用属于π-s型锂键.     

Theoretical Study of the Interplay between Lithium Bond and Hydrogen Bond in Complexes Involved with HLi and HCN

The lithium‐ and hydrogen‐bonded complex of HLi? NCH? NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6‐311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19 % and 61 % for the lithium and hydrogen bonds, respectively. A big cooperative energy (?5.50 kcal mol^?1) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many‐body interaction analysis has also been performed for HLi? (NCH)_N (N=2–5) systems.     

A comparative study of some lithium and hydrogen‐bonded complexes: Ab initio and QTAIM studies

The nature of the interactions of cyanide with lithium and hydrogen halides was investigated using ab initio calculations and topological analysis of electron density. The computed properties of the lithium‐bonded complexes RCN···LiX (R = H, F, Cl, Br, C?CH, CH?CH₂, CH₃, C₂H₅; X = Cl, Br) were compared with those of corresponding hydrogen‐bonded complexes RCN···HX. The results show that both types of intermolecular interactions are “closed‐shell” noncovalent interactions. The effect of substitution on the interaction energy and electron density at the bond critical points of the lithium and hydrogen bonding interactions is similar. In comparison, the interaction energies of lithium‐bonded complexes are more negative than those of hydrogen‐bonded counterparts. The electrostatic interaction plays a more important role in the lithium bond than in the hydrogen bond. On complex formation, the net charge and energy of the Li atom decrease and the atomic volume increases, while the net charge and energy of the H atom increase and the atomic volume decreases. © 2013 Wiley Periodicals, Inc.     

Trimeric cluster of lithium amidoborane—the smallest unit for the modeling of hydrogen release mechanism

A detailed first‐principle DFT M06/6‐311++G(d.p) study of dehydrogenation mechanism of trimeric cluster of lithium amidoborane is presented. The first step of the reaction is association of two LiNH₂BH₃ molecules in the cluster. The dominant feature of the subsequent reaction pathway is activation of H atom of BH₃ group by three Li atoms with formation of unique Li₃H moiety. This Li₃H moiety is destroyed prior to dehydrogenation in favor of formation of a triangular Li₂H moiety, which interacts with protic H atom of NH₂ group. As a result of this interaction, Li₂H₂ moiety is produced. It features N^?? H⁺? H^? group suited near the middle plane between two Li⁺ in the transition state that leads to H₂ release. The transition states of association and hydrogen release steps are similar in energy. It is concluded that the trimer, (LiNH₂BH₃)₃, is the smallest cluster that captures the essence of the hydrogen release reaction. © 2016 Wiley Periodicals, Inc.     

Tuning Hydrogen Storage in Lithium‐Functionalized BC2N Sheets by Doping with Boron and Carbon

First‐principles calculations are used to explore the strong binding of lithium to boron‐ and carbon‐doped BC₂N monolayers (BC₂NB_C and BC₂NC_N, respectively) without the formation of lithium clusters. In comparison to BC₂N and BC₂NC_B, lithium‐decorated BC₂NB_C and BC₂NC_N systems possess stronger s–p and p–p hybridization and, hence, the binding energy is higher. Lithium becomes partially positively charged by donating electron density to the more electronegative atoms of the sheet. Attractive van der Waals interactions are responsible for binding hydrogen molecules around the lithium atoms. Each lithium atom can adsorb three hydrogen molecules on both sides of the sheet, with an average hydrogen binding energy of approximately 0.2 eV, which is in the range required for practical applications. The BC₂NB_C–Li and BC₂NC_N–Li complexes can serve as high‐capacity hydrogen‐storage media with gravimetric hydrogen capacities of 9.88 and 9.94 wt %, respectively.     

Comparing Neutral (Monometallic) and Anionic (Bimetallic) Aluminum Complexes in Hydroboration Catalysis: Influences of Lithium Cooperation and Ligand Set

Bimetallic lithium aluminates and neutral aluminum counterparts are compared as catalysts in hydroboration reactions with aldehydes, ketones, imines and alkynes. Possessing Li–Al cooperativity, ate catalysts are found to be generally superior. Catalytic activity is also influenced by the ligand set, alkyl and/or amido. Devoid of an Al?H bond, iBu₂Al(TMP) operates as a masked hydride reducing benzophenone through a β‐Η transfer process. This catalyst library therefore provides an entry point into the future design of Al catalysts targeting substrate specific transformations.     

Extraordinary superatom containing double shell nucleus: Li(HF)3Li connected mainly by intermolecular interactions

The structure and properties of the Li(HF)₃Li cluster with C_3h symmetry are investigated using ab initio calculations. This Li(HF)₃Li is a metal–nonmetal–metal sandwich‐like cluster connected mainly by the intermolecular interactions. In the special cluster, the (HF)₃ containing the triangular F ring with the negative charges is sandwiched between two Li atom. It is interesting that under the action of the triangular F ring with the negative charges, the valence electrons of two Li atoms are pushed out to form the distended excess electron cloud that surrounds the Li(HF)₃Li as a core. So the Li(HF)₃Li cluster shows not only the electride characteristic, but new superatom characteristics as well. Several characteristics of the special superatom are found. First, the superatom contains the double shell nucleus. The internal nucleus is the regular triangular ring made of three F atoms with the negative charge and the outer‐shell nucleus is made up of three H and two Li atoms with the positive charge. Second, the bonding force of this superatom framework is mainly the intermolecular interaction force, the lithium bond, which is different from that (covalent bond or ionic bond) of the general superatom. Third, the interaction between the outer‐shell nucleus and the excess electron cloud is mainly the anti‐excess‐electron hydrogen bond. Fourth, the special superatom exhibits the new aromaticity (NICS = ?8.37 ppm at the center of the regular triangular F ring), which is the aromaticity found in the cluster of the intermolecular interaction. This is the new knowledge of the aromaticity. Fifth, the large polarizability of the superatom is revealed. Further, the vertical ionization energy (VIE) of the superatom is low, 4.51 eV (<5.210 eV of the alkaline–earth metal Ba) so that it may be viewed as a superalkaline–earth metal atom. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Isolation and Characterization,Including by X‐ray Crystallography,of Contact and Solvent‐Separated Ion Pairs of Silenyl Lithium Species

Reaction of bromoacylsilane 1 (pink solution) with tBu₂MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at ?78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E‐[(tBuMe₂Si)(tBu₂MeSi)C=Si(SiMetBu₂)]^? [Li?4THF]⁺ 2 a (green–blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet–red solution) with two THF molecules bonded to the lithium atom. The 2 a ? 2 b interconversion is reversible upon THF? benzene solvent change. Both 2 a and 2 b were characterized by X‐ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si?Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic ²⁹Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X‐ray molecular structure of both the SSIP and the CIP of any R₂E=E′RM species (E=C, Si; E′=C, Si; M=metal).     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.     

Substitution of Lithium for Magnesium,Zinc, and Aluminum in Li15Si4: Crystal Structures,Thermodynamic Properties,as well as 6Li and 7Li NMR Spectroscopy of Li15Si4 and Li15−xMxSi4 (M=Mg,Zn, and Al)

An investigation into the substitution effects in Li₁₅Si₄, which is discussed as metastable phase that forms during electrochemical charging and discharging cycles in silicon anode materials, is presented. The novel partial substitution of lithium by magnesium and zinc is reported and the results are compared to those obtained for aluminum substitution. The new lithium silicides Li₁₄MgSi₄ ( 1 ) and Li_14.05Zn_0.95Si₄ ( 2 ) were synthesized by high‐temperature reactions and their crystal structures were determined from single‐crystal data. The magnetic properties and thermodynamic stabilities were investigated and compared with those of Li_14.25Al_0.75Si₄ ( 3 ). The substitution of a small amount of Li in metastable Li₁₅Si₄ for more electron‐rich metals, such as Mg, Zn, or Al, leads to a vast increase in the thermodynamic stability of the resulting ternary compounds_. The ^6,7Li NMR chemical shift and spin relaxation time T₁‐NMR spectroscopy behavior at low temperatures indicate an increasing contribution of the conduction electrons to these NMR spectroscopy parameters in the series for 1 – 3 . However, the increasing thermal stability of the new ternary phases is accompanied by a decrease in Li diffusivity, with 2 exhibiting the lowest activation energy for Li mobility with values of 56, 60, and 62 kJ mol^?1 for 2 , Li_14.25Al_0.75Si₁₄, and 1 , respectively. The influence of the metastable property of Li₁₅Si₄ on NMR spectroscopy experiments is highlighted.     

Stabilizing Lithium Plating by a Biphasic Surface Layer Formed In Situ

The dendritic growth of Li metal leads to electrode degradation and safety concerns, impeding its application in building high energy density batteries. Forming a protective layer on the Li surface that is electron‐insulating, ion‐conducting, and maintains an intimate interface is critical. We herein demonstrate that Li plating is stabilized by a biphasic surface layer composed of a lithium‐indium alloy and a lithium halide, formed in situ by the reaction of an electrolyte additive with Li metal. This stabilization is attributed to the fast lithium migration though the alloy bulk and lithium halide surface, which is enabled by the electric field across the layer that is established owing to the electron‐insulating halide phase. A greatly stabilized Li‐electrolyte interface and dendrite‐free plating over 400 hours in Li|Li symmetric cells using an alkyl carbonate electrolyte is demonstrated. High energy efficiency operation of the Li₄Ti₅O₁₂ (LTO)|Li cell over 1000 cycles is achieved.     

Air‐Stable Lithium Spheres Produced by Electrochemical Plating

Lithium metal is an ideal anode for next‐generation lithium batteries owing to its very high theoretical specific capacity of 3860 mAh g^?1 but very reactive upon exposure to ambient air, rendering it difficult to handle and transport. Air‐stable lithium spheres (ASLSs) were produced by electrochemical plating under CO₂ atmosphere inside an advanced aberration‐corrected environmental transmission electron microscope. The ASLSs exhibit a core–shell structure with a Li core and a Li₂CO₃ shell. In ambient air, the ASLSs do not react with moisture and maintain their core–shell structures. Furthermore, the ASLSs can be used as anodes in lithium‐ion batteries, and they exhibit similar electrochemical behavior to metallic Li, indicating that the surface Li₂CO₃ layer is a good Li⁺ ion conductor. The air stability of the ASLSs is attributed to the surface Li₂CO₃ layer, which is barely soluble in water and does not react with oxygen and nitrogen in air at room temperature, thus passivating the Li core.     

Reducing Ga?H and Ga?C Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules

Treatment of [Li(H₂Ga{CH(SiMe₃)₂}₂)] ? 2 OEt₂ ( 1? 2 OEt₂) with two equivalents of tert‐butyl hydrogen peroxide, H‐O‐O‐CMe₃, afforded the organogallium peroxide [({(Me₃Si)₂HC}₂Ga(OH)(OOCMe₃)Li)₂] ( 3 ), which possesses oxidizing peroxo groups in close proximity to reducing Ga? C bonds. The lithium atoms of the dimeric formula units are coordinated by both oxygen atoms of the peroxides and by two hydroxo groups. The cleavage of the Ga? C bond was not observed, even when an excess of H‐O‐O‐CMe₃ was applied. Instead, the adduct [{(Me₃Si)₂HC}₂Ga(OH)(OOCMe₃)₂Li₂(HOOCMe₃)] ( 4 ) was isolated, which has an intact H‐O‐O‐CMe₃ molecule terminally attached to lithium. A similar structural motif was found for the compound [(LiOOCMe₃)₂(HOOCMe₃)₂] ( 5 ). The trihydrido gallanate [Li(H₃Ga? {CH(SiMe₃)₂})] ? OEt₂ ( 2 ) yielded the unique peroxide [({(Me₃Si)₂HC}? Ga(H)(OOCMe₃)₂Li)₂] ( 6 ) under similar conditions that possesses Ga? C and even more reactive Ga? H bonds beside peroxo groups. It decomposed at room temperature by the insertion of oxygen atoms into the Ga? H bonds and the formation of [({(Me₃Si)₂HC}? Ga(OH)(OCMe₃)(OOCMe₃)Li)₂] ( 7 ), which was isolated in a low yield. Further decomposition gave the complete degradation of all peroxo groups with the formation of a relatively complicated Li₄Ga₄O₈ cage ( 8 ).     

[Ge2]4− Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li3NaGe2: A Solid‐State Equivalent to Molecular O2

The novel ternary Zintl phase Li₃NaGe₂ comprises alkali‐metal cations and [Ge₂]^4? dumbbells. The diatomic [Ge₂]^4? unit is characterized by the shortest Ge?Ge distance (2.390(1) Å) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8?N) rule. Raman measurements support these findings. The multiple‐bond character is confirmed by electronic‐structure calculations, and an upfield ⁶Li NMR shift of ?10.0 ppm, which was assigned to the Li cations surrounded by the π systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand‐free dumbbell in Li₃NaGe₂, the π‐ bonding p_y and p_z orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled π‐type bands of the neat solid Li₃NaGe₂ cross the Fermi level, resulting in metallic properties. Li₃NaGe₂ was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.     

Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra

The new stannide Li₂AuSn₂ was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li₂AuSn₂ was investigated by X‐ray diffraction on powders and single crystals and the structure was refined from single‐crystal data: Z=4, I4₁/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F² values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au? Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two‐dimensional AuSn_4/2 layers. The latter are connected in the third dimension through Sn? Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three‐dimensional [AuSn₂] network. Modestly small ⁷Li Knight shifts are measured by solid‐state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the ¹¹⁹Sn Mössbauer spectra and a small chemical shift anisotropy evident from ¹¹⁹Sn solid‐state NMR spectroscopy. Variable‐temperature static ⁷Li solid‐state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature‐dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol^?1.     

Cooperative enhancement of water binding to antiparallel β‐sheet models: Analysis by ab initio calculations

The cooperative enhancement of water binding to the antiparallel β‐sheet models has been studied by quantum chemical calculations at the MP2/6‐311++G**//MP2/6‐31G* level. The binding energies of the two antiparallel β‐sheet models consisting of two strands of diglypeptide are calculated by supermolecular approach. Then water molecules are gradually bonded to the diglypeptide by N? H···OH₂ and C?O···HOH hydrogen bonds. Our calculation results indicated that the hydrogen bond length and the atom charge distribution are affected by the addition of H₂O molecules. The binding energy of antiparallel diglypeptide β‐sheet models has a great improvement by the increasing of the hydrogen bond cooperativity and the more H₂O molecules added the more cooperativity enhancement can be found. The orbital interactions are calculated by natural bond orbital analysis, and the results indicate that the cooperative enhancement is closely related to the orbital interaction. © 2012 Wiley Periodicals, Inc.     

Synthesis and Characterization of a Magnesium Boryl and a Beryllium‐Substituted Diazaborole

Reaction of a lithium boryl, [(THF)₂Li{B(DAB)}] (DAB=[(DipNCH)₂]^2?, Dip=2,6‐diisopropylphenyl), with a dinuclear magnesium(I) compound [{(^MesNacnac)Mg}₂] (^MesNacnac=[HC(MeCNMes)₂]^?, Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, [(^MesNacnac)(THF)Mg{B(DAB)}]. Attempts to prepare the magnesium boryl via a salt metathesis reaction between the lithium boryl and a β‐diketiminato magnesium iodide compound, instead led to an intractable mixture of products. Similarly, reaction of the lithium boryl with a β‐diketiminato beryllium bromide precursor, [(^DepNacnac)BeBr] (Dep=2,6‐diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, [{(^DepNacnac)Be(4‐DAB^?H)}BBr]. For sake of comparison, the same group 2 halide precursor compounds were treated with a potassium gallyl analogue of the lithium boryl, viz. [(tmeda)K{:Ga(DAB)}] (tmeda=N,N,N’,N’‐tetramethylethylenediamine), but no reactions were observed.     

CH3SH和CH3SLi分子间的锂键和氢键共存型相互作用

在CH₃SLi＋CH₃SH势能面上求得锂键和氢键共存型复合物的两种稳定构型. 频率分析表明, 与单体相比复合物中S(5)—Li(6)键伸缩振动频率发生红移, 而C(8)—H(10)键伸缩振动频率发生蓝移. 经B3LYP/6-311＋＋G**, MP2/6-311＋＋G**及MP2/AUG-CC-PVDZ水平计算的含基组重叠误差(BSSE)校正的复合物?中相互作用能分别为－58.99, －57.87和－62.89 kJ•mol^－1. 采用自然键轨道(NBO)理论, 分析了复合物中单体轨道间的电荷转移, 电子密度重排及其与相关键键长变化的本质等. 采用分子中的原子(AIM)理论分析了复合物中氢键和锂键的电子密度拓扑性质．在极化连续模型(PCM)下, 考察了溶剂化效应. 结果表明, 所考察的水、二甲亚砜、乙醇和乙醚等四种溶剂均使单体间的相互作用能增大, 且溶剂对复合物中的锂键结构及其振动频率具有显著的影响, 而对复合物中的氢键的振动频率影响不大.