Synthesis, structure, and magnetic properties of Li-doped manganese-phthalocyanine, Li(x)[MnPc] (0 < or = x < or = 4)

We report on the first synthesis of Li-intercalated manganese-phthalocyanine (MnPc) in the bulk form and on the evolution of the structural and magnetic properties as a function of Li concentration, x. We find that solid beta-MnPc, which comprises rodlike assemblies of individual planar molecules, is best described as a glassy one-dimensional ferromagnet without three-dimensional ordering and that it can be quasi-continuously intercalated with Li up to x = 4, forming an isosymmetrical series of Li(x)[MnPc] phases. Inserted Li+ ions strongly bond to pyrrole-bridging nitrogen atoms of the Pc rings, thereby disrupting the ferromagnetic Mn-N(a)...Mn superexchange pathways. This gradually induces a crossover of the intrachain exchange interactions from ferromagnetic to antiferromagnetic as the doping level, x, increases coupled with a spin-state transition of the Mn2+ ions from intermediate spin, S = 3/2, to high spin, S = 5/2.     

Phase Transformation and Lithiation Effect on Electronic Structure of Li(x)FePO(4): An In-Depth Study by Soft X-ray and Simulations

Through soft X-ray absorption spectroscopy, hard X-ray Raman scattering, and theoretical simulations, we provide the most in-depth and systematic study of the phase transformation and (de)lithiation effect on electronic structure in Li(x)FePO(4) nanoparticles and single crystals. Soft X-ray reveals directly the valence states of Fe 3d electrons in the vicinity of Fermi level, which is sensitive to the local lattice distortion, but more importantly offers detailed information on the evolution of electronic states at different electrochemical stages. The soft X-ray spectra of Li(x)FePO(4) nanoparticles evolve vividly with the (de)lithiation level. The spectra fingerprint the (de)lithiation process with rich information on Li distribution, valency, spin states, and crystal field. The high-resolution spectra reveal a subtle but critical deviation from two-phase transformation in our electrochemically prepared samples. In addition, we performed both first-principles calculations and multiplet simulations of the spectra and quantitatively determined the 3d valence states that are completely redistributed through (de)lithiation. This electronic reconfiguration was further verified by the polarization-dependent spectra collected on LiFePO(4) single crystals, especially along the lithium diffusion direction. The evolution of the 3d states is overall consistent with the local lattice distortion and provides a fundamental picture of the (de)lithiation effects on electronic structure in the Li(x)FePO(4) system.     

Small polaron hopping in Li(x)FePO4 solid solutions: coupled lithium-ion and electron mobility

Transition metal phosphates such as LiFePO(4) have been recognized as very promising electrodes for lithium-ion batteries because of their energy storage capacity combined with electrochemical and thermal stability. A key issue in these materials is to unravel the factors governing electron and ion transport within the lattice. Lithium extraction from LiFePO(4) results in a two-phase mixture with FePO(4) that limits the power characteristics owing to the low mobility of the phase boundary. This boundary is a consequence of low solubility of the parent phases, and its mobility is impeded by slow migration of the charge carriers. In principle, these limitations could be diminished in a solid solution, Li(x)FePO(4). Here, we show that electron delocalization in the solid solution phases formed at elevated temperature is due to rapid small polaron hopping and is unrelated to consideration of the band gap. We give the first experimental evidence for a strong correlation between electron and lithium delocalization events that suggests they are coupled. Furthermore, the exquisite frequency sensitivity of M?ssbauer measurements provides direct insight into the electron hopping rate.     

Planarity takes over in the C(x)H(x)P(6-x) (x = 0-6) series at x = 4

In this work we examine a structural transition from non-planar three-dimensional structures to planar benzene-like structures in the C(x)H(x)P(6-x) (x = 0-6) series. The global minima of P(6), CHP(5), and C(2)H(2)P(4) species are benzvalene-like structures. The benzvalene and benzene-like structures of C(3)H(3)P(3) are close in energy with the former being slightly more stable at our best level of theory. The transition occurs at x = 4 (C(4)H(4)P(2)), where the benzene-like structures become significantly more stable than the benzvalene-like structures. We show that the pseudo Jahn-Teller effect, which is responsible for the deformation of planar P(6), CHP(5), and C(2)H(2)P(4) structures, is completely suppressed at x = 3 (benzene-like structures of C(3)H(3)P(3)). We present NICS(zz) values of all the benzene-like isomers in the series.     

Hydrothermal synthesis, thermal, and magnetic data on new alkaline vanadium phosphate My(VO)9 + x(PO4)4x(HPO4)12 - 4x with M = Cs+ (y = 5.29, x = 1) and M = NH4+, Rb+ (y approximately 5, x approximately 1)

Brownish platelet crystals of My(VO)9 + x(PO4)4x(HPO4)12 - 4x (M = Cs+, NH4+ and Rb+) were prepared hydrothermally. The structure of Cs approximately 5(VO)10(PO4)4(HPO4)8 was solved from single-crystal X-ray diffraction data in the centrosymmetric monoclinic space group C2/c (No. 15) a = 21.1951(8) A, b = 12.2051(4) A, c = 20.6230(8) A, beta = 109.742(2) degrees, Z = 4 (R1(Fo) = 0.054, wR2(Fo2) = 0.123). The structure of Cs approximately 5(VO)10(PO4)4(HPO4)8 is described and compared to that of K2(VO)3(HPO4)4 previously reported by Lii. For the three compounds, thermogravimetric data and susceptibility measurements were investigated and were found to be in agreement with the structural study.     

Die Reaktionen von M[BF4] (M = Li,K) und (C2H5)2O·BF3 mit (CH3)3SiCN. Bildung von M[BFx>(CN)4—x] (M = Li,K; x = 1, 2) und (CH3)3SiNCBFx(CN)3—x, (x = 0, 1)

The Reactions of M[BF₄] (M = Li, K) and (C₂H₅)₂O·BF₃ with (CH₃)₃SiCN. Formation of M[BF_x(CN)_4—x] (M = Li, K; x = 1, 2) and (CH₃)₃SiNCBF_x(CN)_3—x, (x = 0, 1) The reaction of M[BF₄] (M = Li, K) with (CH₃)₃SiCN leads selectively, depending on the reaction time and temperature, to the mixed cyanofluoroborates M[BF_x(CN)_4—x] (x = 1, 2; M = Li, K). By using (C₂H₅)₂O·BF₃ the synthesis yields the compounds (CH₃)₃SiNCBF_x(CN)_3—x x = 0, 1. The products are characterized by vibrational and NMR‐spectroscopy, as well as by X‐ray diffraction of single‐crystals: Li[BF₂(CN)₂]·2Me₃SiCN Cmc2₁, a = 24.0851(5), b = 12.8829(3), c = 18.9139(5) Å V = 5868.7(2) ų, Z = 12, R₁ = 4.7%; K[BF₂(CN)₂] P4₁2₁2, a = 13.1596(3), c = 38.4183(8) Å, V = 6653.1(3) ų, Z = 48, R₁ = 2.5%; K[BF(CN)₃] P1¯, a = 6.519(1), b = 7.319(1), c = 7.633(2) Å, α = 68.02(3), β = 74.70(3), γ = 89.09(3)°, V = 324.3(1) ų, Z = 2, R₁ = 3.6%; Me₃SiNCBF(CN)₂ Pbca, a = 9.1838(6), b = 13.3094(8), c = 16.840(1) Å, V = 2058.4(2) ų, Z = 8, R₁ = 4.4%     

Electronic structure and thermochemical properties of small neutral and cationic lithium clusters and boron-doped lithium clusters: Li(n)(0/+) and Li(n)B(0/+) (n = 1-8)

The stability, electronic structure, and thermochemical properties of the pure Li(n) and boron-doped Li(n)B (n = 1-8) clusters in both neutral and cationic states are studied using electronic structure methods. The global equilibrium structures are established, and their heats of formation are evaluated using the G3B3 and CCSD(T)/CBS methods based on the density functional theory geometries. Theoretical adiabatic ionization energies (IE(a)) for the Li(n) clusters are in good agreement with experiment: Li(2) (G3B3, 5.21 eV; CCSD(T), 5.14 eV; expt, 5.1127 ± 0.0003 eV), Li(3) (4.16, 4.11, 4.08 ± 0.10), Li(4) (4.76, 4.68, 4.70 ± 0.05), Li(5) (4.11, 4.06, 4.02 ± 0.10), Li(6) (4.46, 4.32, 4.20 ± 0.10), Li(7) (4.07, 3.99, 3.94 ± 0.10), and Li(8) (4.49, 4.31, 4.16 ± 0.10). The Li(4) experimental IE(a) has been revised on the basis of the Franck-Condon simulations. Species Li(5)B, Li(6)B(+), Li(7)B, and Li(8)B(+) exhibit high stability as compared to their neighbors, which can be understood by considering the magic numbers of the phenomenological shell model (PSM).     

Relationship between the electrochemical behavior and Li arrangement in Li(x)M(y)Mn(2-y)O4 (M = Co, Cr) with spinel structure

The relationship between the electrochemical behavior and the arrangement of lithium/vacancies has been investigated with electrochemical Li removal in Li(x)M(y)Mn(2-y)O4 (x < or = 1.0, 0.0 < or = y < or = 0.3, M = Co, Cr). It was shown that the electrochemical removal proceeds via two voltage regions: (1) approximately 3.9 V at x > or = approximately 0.5 and (2) approximately 4.2 V at x < or = approximately 0.5. To understand the stepwise behavior, entropy measurement of reaction, DeltaS(obs), was performed by using the electrochemical methods. The changes of the sign in deltaS(obs) from negative to positive at the composition x approximately 0.50 in Li(x)M(y)Mn(2-y)O4 indicated that the ordered arrangement of Li/vacancies was formed with electrochemical Li removal. Moreover, such an ordering was suppressed by the substitution of Co3+ and Cr3+ for Mn3+. To clarify the nature and origin of Li/vacancy ordering, the Monte Carlo simulation was performed in view of Coulombic interaction. The simulation reproduced the formation of a new phase arising from Li/vacancy ordering at x = 0.50 in Li(x)Mn2O4. In addition, the ordered arrangement of Li/vacancy at x = 0.5 was perturbed by the trivalent M3+ replacement in spinel structure due to the local clustering of Li+ around M3+. Consequently, the electrochemical behavior in spinel LiMn2O4 was deeply related to the Coulombic interactions, proved by the fact that experimentally observed changes in entropy agreed well with Monte Carlo simulation based on the Coulombic interaction.     

Atmospheric chemistry of n-C(x)F(2)(x)(+1)CHO (x = 1, 2, 3, 4): fate of n-C(x)F(2)(x)(+1)C(O) radicals

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C(x)F(2)(x)(+1)C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O(2)/N(2) diluent at 298 +/- 3 K. A competition is observed between reaction with O(2) to form n-C(x)()F(2)(x)()(+1)C(O)O(2) radicals and decomposition to form n-C(x)F(2)(x)(+1) radicals and CO. In 700 Torr O(2)/N(2) diluent at 298 +/- 3 K, the rate constant ratio, k(n-C(x)F(2)(x)(+1)C(O) + O(2) --> n-C(x)F(2)(x)(+1)C(O)O(2))/k(n-C(x)F(2)(x)(+1)C(O) --> n-C(x)F(2)(x)(+1) + CO) = (1.30 +/- 0.05) x 10(-17), (1.90 +/- 0.17) x 10(-19), (5.04 +/- 0.40) x 10(-20), and (2.67 +/- 0.42) x 10(-20) cm(3) molecule(-1) for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O(2) accounts for 99%, 50%, 21%, and 12% of the loss of n-C(x)F(2)(x)(+1)C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C(x)F(2)(x)(+1)C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.     

Cathodic materials for lithium-ion batteries based on spinels Li x Mn2−y Me y O4: Synthesis, phase composition, and structure of Li x Mn2−y Cr y O4 at x = 1.0−1.2 and y = 0−0.5

Extralithiated chromium-doped finely divided lithium-manganese spinels are synthesized as a result of a two-step solid-phase process with use made of the fusion-saturation method. The spinels are intended for application as cathodic materials in lithium-ion batteries. The phase composition and structural characteristics of samples of cathodic materials of the type Li _x Mn_2?y Cr _y O₄ are studied. The samples with x = 1.0?1.2 and y = 0?0.5 are characterized by phase purity and cubic syngony with parameter a = 0.817?0.823 nm and a disperseness equal to 1–2 nm. The maximum content of chromium and lithium in Li _x Mn_2?y Cr _y O₄ that does not lead to violation of cubic syngony is determined. Lithium excess in the cathodic material that does not exceed 0.2 formula units may be used for compensating the irreversible capacity. Replacing some manganese atoms by chromium may facilitate retention of the structures’s integrity in the course of cycling.     

Six-dimensional quantum dynamics of (v=0,j=0)D2 and of (v=1,j=0)H2 scattering from Cu111

We report six-dimensional quantum dynamics calculations of the dissociative scattering of molecular hydrogen from the copper111 surface. Two potential energy surfaces are investigated and the results are compared with experiment. Our study completes the preliminary work of Somers et al. [Chem. Phys. Lett. 360, 390 (2002)] and focuses on the role of initial vibrational excitation and on isotopic effects. None of the two investigated potential energy surfaces is found satisfactory: the use of neither potential yields reaction and vibrational excitation probabilities and vibrational efficacies that are in close agreement with experiment. In addition to showing the shortcomings of existing potential energy surfaces we point out an inconsistency in the experimental fits for D2.     

Structural and thermochemical chemisorption of CO2 on Li(4+x)(Si(1-x)Al(x))O4 and Li(4-x)(Si(1-x)V(x))O4 solid solutions

Different Li(4)SiO(4) solid solutions containing aluminum (Li(4+x)(Si(1-x)Al(x))O(4)) or vanadium (Li(4-x)(Si(1-x)V(x))O(4)) were prepared by solid state reactions. Samples were characterized by X-ray diffraction and solid state nuclear magnetic resonance. Then, samples were tested as CO(2) captors. Characterization results show that both, aluminum and vanadium ions, occupy silicon sites into the Li(4)SiO(4) lattice. Thus, the dissolution of aluminum is compensated by Li(1+) interstitials, while the dissolution of vanadium leads to lithium vacancies formation. Finally, the CO(2) capture evaluation shows that the aluminum presence into the Li(4)SiO(4) structure highly improves the CO(2) chemisorption, and on the contrary, vanadium addition inhibits it. The differences observed between the CO(2) chemisorption processes are mainly correlated to the different lithium secondary phases produced in each case and their corresponding diffusion properties.     

Darstellung und Kristallstruktur der Phasen Li26Na58Ba38Ex (E = N,H; x = 0 – 1)

Preparation and Crystal Structures of Li₂₆Na₅₈Ba₃₈E_x Phases (E = N, H; x = 0 – 1) Li₂₆Na₅₈Ba₃₈E_x (E = N, H; x = 0–1) were prepared as a majority phase by the reactions of the metals with Ba(N₃)₂ or BaH₂ at 250 °C for five days. According to single crystal and powder X‐ray diffraction investigation, all compounds are cubic, space group with the unit cell parameter a ranging from 27.335(2) (x = 0) to 27.554(3) (x = 1, E = N, H) Å and Z = 4. This compound series can be described as a filled variant of Li₁₃Na₂₉Ba₁₉, in which nitrogen or hydrogen atoms are found in the centre of Li₂₆ clusters in tetrahedral environment. Li₂₆Na₅₈Ba₃₈E_x represents a new group of metal‐rich compounds extending the growing family of subnitrides.     

Synthesis and characterization of the variable-composition phase Na1−x Ni1−x Cr1+x (MoO4)3 (0 ≤ x ≤ 0.4) with a NASICON structure

Synthetic conditions are determined for the variable-composition phase Na_1?x Ni_1?x Cr_1+x (MoO₄)₃ (0 ≤ x ≤ 0.4) with a NASICON structure. The unit cell parameters of this phase are derived from X-ray powder diffraction data, and the phase is characterized by IR and Raman spectroscopy.     

Electronic structure and thermochemical properties of silicon-doped lithium clusters Li(n)Si0/+, n = 1-8: new insights on their stability

A theoretical investigation on small silicon-doped lithium clusters Li(n)Si with n = 1-8, in both neutral and cationic states is performed using the high accuracy CCSD(T)/complete basis set (CBS) method. Location of the global minima is carried out using a stochastic search method and the growth pattern of the clusters emerges as follows: (i) the species Li(n)Si with n ≤ 6 are formed by directly binding one Li to a Si of the smaller cluster Li(n-1)Si, (ii) the structures tend to have an as high as possible symmetry and to maximize the coordination number of silicon. The first three-dimensional global minimum is found for Li(4)Si, and (iii) for Li(7)Si and Li(8)Si, the global minima are formed by capping Li atoms on triangular faces of Li(6)Si (O(h)). A maximum coordination number of silicon is found to be 6 for the global minima, and structures with higher coordination of silicon exist but are less stable. Heats of formation at 0 K (Δ(f)H(0)) and 298 K (Δ(f)H(298)), average binding energies (E(b)), adiabatic (AIE) and vertical (VIE) ionization energies, dissociation energies (D(e)), and second-order difference in total energy (Δ(2)E) of the clusters in both neutral and cationic states are calculated from the CCSD(T)/CBS energies and used to evaluate the relative stability of clusters. The species Li(4)Si, Li(6)Si, and Li(5)Si(+) are the more stable systems with large HOMO-LUMO gaps, E(b), and Δ(2)E. Their enhanced stability can be rationalized using a modified phenomenological shell model, which includes the effects of additional factors such as geometrical symmetry and coordination number of the dopant. The new model is subsequently applied with consistency to other impure clusters Li(n)X with X = B, Al, C, Si, Ge, and Sn.