Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

水合氢离子团簇从头算和ABEEM/MM的理论研究

应用高水平的从头计算方法和ABEEM/MM模型, 研究了水合氢离子团簇H3O＋(H2O)n (n＝1～6), 优化得到了低能构象, 探讨了其结合能和稳定性, 显示出H3O＋(H2O)3局域结构的优势存在．对H3O＋(H2O)6VIa团簇的ABEEM电荷分布进行分析, 表明第一水合层水分子与水合氢离子之间的氢键相互作用要明显强于与第二水层水分子的氢键相互作用. 研究结果表明, ABEEM/MM方法计算的结果和从头算得到的结果存在很好的一致性.     

Structure and photoabsorption properties of cationic alkali dimers solvated in neon clusters

We present a theoretical investigation of the structure and optical absorption of M(2)(+) alkali dimers (M=Li,Na,K) solvated in Ne(n) clusters for n=1 to a few tens Ne atoms. For all these alkali, the lowest-energy isomers are obtained by aggregation of the first Ne atoms at the extremity of the alkali molecule. This particular geometry, common to other M(2)(+)-rare gas clusters, is intimately related to the shape of the electronic density of the X (2)Σ(g)(+) ground state of the bare M(2)(+) molecules. The structure of the first solvation shell presents equilateral Ne(3) and capped pentagonal Ne(6) motifs, which are characteristic of pure rare gas clusters. The size and geometry of the complete solvation shell depend on the alkali and were obtained at n=22 with a D(4h) symmetry for Li and at n=27 with a D(5h) symmetry for Na. For K, our study suggests that the closure of the first solvation shell occurs well beyond n=36. We show that the atomic arrangement of these clusters has a profound influence on their optical absorption spectrum. In particular, the XΣ transition from the X (2)Σ(g)(+) ground state to the first excited (2)Σ(u)(+) state is strongly blueshifted in the Frank-Condon area.     

Ion-molecule interactions in solutions of lithium perchlorate in propylene carbonate + diethyl carbonate mixtures: an IR and molecular orbital study

FTIR spectra have been recorded and analyzed for solutions of lithium perchlorate in propylene carbonate (PC), diethyl carbonate (DEC), and PC + DEC mixtures. It has been shown that the carbonyl stretch bands for PC and DEC are very sensitive to the interaction between Li+ and the solvent molecules. They split with addition of LiClO4, indicating a strong interaction of Li+ with PC and DEC through the oxygen group of PC and both oxygen and ether oxygen atoms of DEC. In conjunction with molecular orbital calculation, the optimized geometries of solvation are given. In addition, solvent separated ion pairs and contact ion pairs were observed in LiClO4/DEC solutions, and no preferential solvation of Li+ in LiClO4/PC + DEC solutions were detected.     

HCl solvation at the surface and within methanol clusters/nanoparticles II: Evidence for molecular wires

Condensed-phase solvation of HCl on and within methanol nanoparticles was investigated by Fourier transform infrared (FTIR) spectroscopy, on-the-fly molecular dynamics as implemented in the density functional code Quickstep (which is part of the CP2K package), and ab initio calculations. Adsorption and solvation stages are identified and assigned with the help of calculated infrared spectra obtained from the simulations. The results have been further checked with MP2-level ab initio calculations. The range of acid solvation states extends from the single-coordinated slightly stretched HCl to proton-sharing with Zundel-like methanol O...H+...X- states, and finally to MeOH2+...Cl- units with full proton transfer. Furthermore, once the proton moves to methanol, it is mobilized along methanol molecular chains. Since the proton dynamics reflects the evolving local structures, the "proton" spectra display broad bands usually with underlying continua.     

Infrared spectroscopy of Li(NH3)n clusters for n=4-7

Infrared spectra of Li(NH3)(n) clusters as a function of size are reported for the first time. Spectra have been recorded in the N-H stretching region for n=4-->7 using a mass-selective photodissociation technique. For the n=4 cluster, three distinct IR absorption bands are seen over a relatively narrow region, whereas the larger clusters yield additional features at higher frequencies. Ab initio calculations have been carried out in support of these experiments for the specific cases of n=4 and 5 for various isomers of these clusters. The bands observed in the spectrum for Li(NH3)(4) can all be attributed to N-H stretching vibrations from solvent molecules in the first solvation shell. The appearance of higher frequency N-H stretching bands for n > or =5 is assigned to the presence of ammonia molecules located in a second solvent shell. These data provide strong support for previous suggestions, based on gas phase photoionization measurements, that the first solvation shell for Li(NH3)(n) is complete at n=4. They are also consistent with neutron diffraction studies of concentrated lithium/liquid ammonia solutions, where Li(NH3)(4) is found to be the basic structural motif.     

The coordination of uranyl in water: a combined quantum chemical and molecular simulation study

The coordination environment of uranyl in water has been studied using a combined quantum mechanical and molecular dynamics approach. Multiconfigurational wave function calculations have been performed to generate pair potentials between uranyl and water. The quantum chemically determined energies have been used to fit parameters in a polarizable force field with an added charge transfer term. Molecular dynamics simulations have been performed for the uranyl ion and up to 400 water molecules. The results show a uranyl ion with five water molecules coordinated in the equatorial plane. The U-O(H(2)O) distance is 2.40 A, which is close to the experimental estimates. A second coordination shell starts at about 4.7 A from the uranium atom. No hydrogen bonding is found between the uranyl oxygens and water. Exchange of waters between the first and second solvation shell is found to occur through a path intermediate between association and interchange. This is the first fully ab initio determination of the solvation of the uranyl ion in water.     

Ab initio QM/MM simulation of Ag+ in 18.6% aqueous ammonia solution: structure and dynamics investigations

Structure and dynamics investigations of Ag(+) in 18.6% aqueous ammonia solution have been carried out by means of the ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulation method. The most important region, the first solvation shell, was treated by ab initio quantum mechanics at the Restricted Hartree-Fock (RHF) level using double-zeta plus polarization basis sets for ammonia and plus ECP for Ag(+). For the remaining region in the system, newly constructed three-body corrected potential functions were used. The average composition of the first solvation shell was found to be [Ag(NH(3))(2)(H(2)O)(2.8)](+). No ammonia exchange process was observed for the first solvation shell, whereas ligand exchange processes occurred with a very short mean residence time of 1.1 ps for the water ligands. No distinct second solvation shell was observed in this simulation.     

水环境对GC和AT碱基对质子转移的影响

采用B3LYP/DZP++的方法研究了第一水化层作用和连续化处理的水溶剂作用对鸟嘌呤-胞嘧啶(GC)碱基对和腺嘌呤-胸腺嘧啶(AT)碱基对质子转移反应的影响. GC和AT碱基对在连续化水溶剂作用下,均发生单质子转移(SPT1)和分步的双质子转移(DPT),而在第一水化层5 个水分子的作用下(GC·5H₂O,AT·5H₂O)或同时考虑第一水化层作用和连续化水溶剂作用(GC·5H₂O+PCM,AT·5H₂O+PCM)时,GC和AT碱基对的质子转移均只得到单质子转移反应(SPT1). 单质子转移过程中的活化能变化情况表明：第一水化层对GC和AT碱基对结构和质子转移影响较大,水环境对碱基对的作用主要发生在第一水化层.     

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium‐Ion Battery Electrolytes

Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li⁺ with pure carbonates and ethylene carbonate (EC)‐based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06‐2X/6‐311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li‐ion solvation in carbonates and EC‐based mixtures. A strong local tetrahedral order involving four carbonates around the Li⁺ was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li⁺ ion with carbonates are negative and suggested the ion–carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li⁺ interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO‐EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li⁺ ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO‐EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li‐ion batteries, which complies with experiments and other theoretical results.     

Understanding microsolvation of Li+: structural and energetical analyses

A stochastic exploration of the quantum conformational space for the (H(2)O)(n)Li(+), n = 3, 4, 5 complexes produced 32 molecular clusters at the B3LYP/6-311++G** and MP2/6-311++G** levels. The first solvation shell is predicted to comprise a maximum of 4 water molecules. Energy decomposition analyses were performed to determine the relationship between the geometrical features of the complexes and the types of interactions responsible for their stabilization. Our findings reveal that electrostatic interactions are major players determining the structures and relative stabilities of the clusters. The formal charge on the Li atom leads to two distinct types of hydrogen bonds, scattered in a wide range of distances (1.61-2.32 ?), in many cases affording H-bonds that are considerably larger and considerably shorter than those in pure water clusters (typically ～1.97 ?).     

Ab initio studies on the mechanism of the size-dependent hydrogen-loss reaction in Mg+(H2O)n

The mechanism of size-dependent intracluster hydrogen loss in the cluster ions Mg(+)(H(2)O)(n), which is switched on around n=6, and off around n=14, was studied by ab initio calculations at the MP2/6-31G* and MP2/6-31G** levels for n=1-6. The reaction proceeds by Mg(+)-assisted breaking of an H-O bond in one of the H(2)O molecules. The reaction barrier is dependent on both the cluster size and the solvation structure. As n increases from 1 to 6, there is a dramatic drop in the reaction barrier, from greater than 70 kcal mol(-1) for n=1 to less than 10 kcal mol(-1) for n=6. In the transition structures, the Mg atom is close to the oxidation state of +2, and H(2)O molecules in the first solvation shell are much more effective in stabilizing the transition structures and lowering the reaction barriers than H(2)O molecules in the other solvation shells. While the reaction barrier for trimer core structures with only three H(2)O molecules in the first shell is greater than 24 kcal mol(-1), even for Mg(+)(H(2)O)(6), it drops considerably for clusters with four-six H(2)O molecules in the first shell. The more highly coordinated complexes have comparable or slightly higher energy than the trimer core structures, and the presence of such high coordination number complexes is the underlying kinetic factor for the switching on of the hydrogen-loss reaction around n=6. For clusters with trimer core structures, the hydrogen loss reaction is much easier when it is preceded by an isomerization step that increases the coordination number around Mg(+). Delocalization of the electron on the singly occupied molecular orbital (SOMO) away from the Mg(+) ion is observed for the hexamer core structure, while at the same time this isomer is the most reactive for the hydrogen-loss reaction, with an energy barrier of only 2.7 kcal mol(-1) at the MP2/6-31G** level.     

Monte Carlo simulation of a 1,4,7,10-tetraazacyclododecane/lithium complex in aqueous solution

Monte Carlo simulations have been carried out for the system consisting of a 1,4,7,10-tetraazacyclododecane (cyclen)-lithium complex in 201 water molecules. The volume of the periodic cube was calculated using the experimental density of pure water at 298 K and 1 atm of 1 g.cm(-)(3), plus additional space occupied by the complex. The geometry of the complex is the alternated form, where the ion is located at the center of the cyclen. The complex-water interaction was represented by the cyclen-water and lithium-water pair potentials, both of which were developed on the basis of ab initio calculations. The results show two layers of solvation shells consisting of 2 and 6.9 water molecules. Two water molecules in the first solvation shell (O(1) and O(2)) bind directly to the ion in which the ion-oxygen distance is 2.38 A, the dipole vector points to the ion, and rotation takes place around the ion-oxygen axis. In the next layer, 4 water molecules coordinate simultaneously to the first 2 water molecules in the first shell and the NH functional groups of cyclen. The remaining 2.9 water molecules in the second layer are also coordinated to be in the first half-hydration shell of O(1) and O(2).     

A first principles molecular dynamics study of lithium atom solvation in binary liquid mixture of water and ammonia: structural, electronic, and dynamical properties

The preferential solvation of solutes in mixed solvent systems is an interesting phenomenon that plays important roles in solubility and kinetics. In the present study, solvation of a lithium atom in aqueous ammonia solution has been investigated from first principles molecular dynamics simulations. Solvation of alkali metal atoms, like lithium, in aqueous and ammonia media is particularly interesting because the alkali metal atoms release their valence electrons in these media so as to produce solvated electrons and metal counterions. In the present work, first principles simulations are performed employing the Car-Parrinello molecular dynamics method. Spontaneous ionization of the Li atom is found to occur in the mixed solvent system. From the radial distribution functions, it is found that the Li(+) ion is preferentially solvated by water and the coordination number is mostly four in its first solvation shell and exchange of water molecules between the first and second solvation shells is essentially negligible in the time scale of our simulations. The Li(+) ion and the unbound electron are well separated and screened by the polar solvent molecules. Also the unbound electron is primarily captured by the hydrogens of water molecules. The diffusion rates of Li(+) ion and water molecules in its first solvation shell are found to be rather slow. In the bulk phase, the diffusion of water is found to be slower than that of ammonia molecules because of strong ammonia-water hydrogen bonds that participate in solvating ammonia molecules in the mixture. The ratio of first and second rank orientational correlation functions deviate from 3, which suggests a deviation from the ideal Debye-type orientational diffusion. It is found that the hydrogen bond lifetimes of ammonia-ammonia pairs is very short. However, ammonia-water H-bonds are found to be quite strong when ammonia acts as an acceptor and these hydrogen bonds are found to live longer than even water-water hydrogen bonds.     

Coordination structures of lithium-methylamine clusters from infrared spectroscopy and ab initio calculations

Spectra of clusters formed between lithium atoms and methylamine molecules are reported for the first time. Mass-selective infrared spectra of Li(NH(2)CH(3))(n) have been recorded in both the N-H and C-H stretching fundamental regions. The infrared spectra are broadly in agreement with ab initio predictions, showing redshifted N-H stretching bands relative to free methylamine and a strong enhancement of the N-H stretching fundamentals relative to the C-H stretching fundamentals. The ab initio calculations suggest that, for n=3, the methylamine molecules bunch together on one side of the lithium atom to minimize repulsive interactions with the unpaired electron density. The addition of a fourth methylamine molecule results in closure of the inner solvation shell and, thus, Li(NH(2)CH(3))(5) is forced to adopt a two-shell coordination structure. This is consistent with neutron diffraction studies of concentrated lithium/methylamine solutions, which also suggest that the first solvation shell around the lithium atom can contain a maximum of four methylamine molecules.     

Synthesis, crystal structure, and nonlinear optical properties of Li6CuB4O10: a congruently melting compound with isolated [CuB4O10]6- units

Single crystals of Li(6)CuB(4)O(10) have been synthesized, and its crystal structure has been determined. Li(6)CuB(4)O(10) crystallizes in the non-centrosymmetric triclinic space group P1 (No. 1). The structure consists of isolated [CuB(4)O(10)](6)(-) polyanions that are bridged by six LiO(4) tetrahedra. Li(6)CuB(4)O(10) is a congruently melting compound. It produces SHG intensity similar to that produced by KH(2)PO(4) and is phase-matchable.     

Solvation of uranyl(II) and europium(III) cations and their chloro complexes in a room-temperature ionic liquid. A theoretical study of the effect of solvent "humidity"

We report a molecular dynamics study of the solvation of the UO2(2+) and Eu3+ cations and their chloro complexes in the [BMI][PF6][H2O] "humid" room-temperature ionic liquid (IL) composed of 1-butyl-3-methylimidazolium+ and PF6- ions and H2O in a 1:1:1 ratio. When compared to the results obtained in dry [BMI][PF6], the present results reveal the importance of water. The "naked" cations form UO2(H2O)5(2+) and Eu(H2O)9(3+) complexes, embedded in a shell of 7 and 8 PF6- anions, respectively. All studied UO2Cln(2-n) and EuCln(3-n) chloro complexes remain stable during the dynamics and coordinate additional H2O molecules in their first shell. UO2Cl4(2-) and EuCl6(3-) are surrounded by an "unsaturated" water shell, followed by a shell of BMI+ cations. According to an energy component analysis, the UO2Cl4(2-) and EuCl6(3-) species, intrinsically unstable toward dissociation, are more stable than their less halogenated analogues in the IL solution, due to the solvation forces. The different chloro species also interact better with the humid than with the dry IL, which hints at the importance of solvent humidity to improve their solubility. Humidity markedly modifies the local ion environment, with major consequences as far as their spectroscopic properties are concerned. We finally compare the aqueous interface of [BMI][PF6] and [OMI][PF6] ionic liquids, demonstrating the importance of imidazolium substituents (N-butyl versus N-octyl) to the nature of the interface and miscibility with water.     

Hydration of alkali ions from first principles molecular dynamics revisited

Structural and dynamical properties of the hydration of Li(+), Na(+), and K(+) in liquid water at ambient conditions were studied by first principles molecular dynamics. Our simulations successfully captured the different hydration behavior shown by the three alkali ions as observed in experiments. The present analyses of the dependence of the self-diffusion coefficient and rotational correlation time of water on the ion concentration suggest that Li(+) (K(+)) is certainly categorized as a structure maker (breaker), whereas Na(+) acts as a weak structure breaker. An analysis of the relevant electronic structures, based on maximally localized Wannier functions, revealed that the dipole moment of H(2)O molecules in the first solvation shell of Na(+) and K(+) decreases by about 0.1 D compared to that in the bulk, due to a contraction of the oxygen lone pair orbital pointing toward the metal ion.     

Vibrational spectroscopy and ab initio studies of lithium bis(oxalato)borate (LiBOB) in different solvents

The effect of lithium ion coordination with the bis(oxalato)borate (BOB-) [B(C2O4)2]- anion in DMSO, PEG, PPG, and d-PPG has been studied in detail by IR and Raman spectroscopy. Ab initio calculations were performed to allow a consistent analysis of the experimental data. The main features observed in the IR and Raman spectra correspond to the presence of "free", un-coordinated, BOB- anions. Only with use of d-PPG as solvent a small amount of Li+...BOB- ion pairs were detected. The Raman spectra and the calculations together indicate that Li+ coordinates bidentately with two end-oxygen atoms of the BOB- anion. The identification of ion pairs can be used to reveal limitations of LiBOB based electrolytes. The results for LiBOB are compared with literature on other Li salts.