Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Relative permittivity increments for {xCH3OH + (1 − x)CH3OCH2(CH2OCH2)3CH2OCH3} fromT = 283.15 K toT = 323.15 K

Relative permittivities of { CH₃OH  +  CH₃OCH₂(CH₂OCH₂)₃CH₂OCH₃(2,5,8,11,14-pentaoxapentadecane, tegdme)} at temperatures from 283.15 K to 323.15 K and atmospheric pressure, were measured over the whole composition range. Experimental relative permittivities were fitted by a polynomial function in mole fraction. Values of relative permittivity were measured using a HP4284A precision LCR Meter together with the measuring cell HP16452A at 1 MHz. Relative permittivity increments were determined from experimental data and fitted to a variable-degree polynomial function. Different theoretical models were used to predict the permittivity of this mixture. The predictions are better when the volume change on mixing is considered.     

Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.     

Thermodynamic study of (alkyl esters + α,ω-alkyl dihalides) III. HmEandVmE for 20 binary mixtures {xCu − 1H2u − 1CO2C4H9 + (1 − x)α,ω-ClCH2(CH2)v − 2CH2Cl}, where u = 1 to 4, α = 1 and v = ω = 2 to 6

In this article, the experimental data of excess molar enthalpies $H_{\mathrm{m}}^{\mathrm{E}}$ and excess molar volumes $V_{\mathrm{m}}^{\mathrm{E}}$ are presented for a set of 20 binary mixtures comprised of the first four butyl alkanoates (methanoate to butanoate) and five α,ω-dichloroalkanes (1,2-dichloroethane to 1,6-dichlorohexane), obtained at atmospheric pressure and at a temperature of 298.15 K. The results indicate the existence of specific interactions between both kinds of compounds resulting in exothermic processes for most mixtures, except for those containing butyl methanoate which give rise to net endo/exothermic effects. The $V_{\mathrm{m}}^{\mathrm{E}}$ are positive for mixtures of (butyl esters + 1,2-dichloroethane or 1,3-dichloropropane) and negative for the remaining ones. The change in $H_{\mathrm{m}}^{\mathrm{E}}$ with the dichloroethane chain length for a same ester is regular although the $V_{\mathrm{m}}^{\mathrm{E}}$ presents an irregular variation. It can, therefore, be deuced from this that the mixing process involves both effects, exothermic/endothermic and expansion/contraction, simultaneously. The behaviour of the mixtures is interpreted on the basis of the results observed and attributed to different effects taking place among the molecules studied.To improve application of the UNIFAC model using the version of Dang and Tassios, average values were recalculated again for parameters of the ester/chloride interaction, distinguishing, during its application, the functional group of the acid part of the ester. In spite of this, the model does not adequately reproduce the systems’ behaviour.     

Diels-Alder reaction with cyclopentadiene and electronic structures of (η5-cyclopentadienyl)M(CO)x(η1-N-maleimidato) (M = Fe,Mo, W,x = 2 or 3)

Diels-Alder reaction of (η⁵-cyclopentadienyl)M(CO)_x(η¹-N-maleimidato) complexes (M = Fe, Mo, W, x = 2 or 3) with cyclopentadiene has been studied. The observed order of reactivity was: N-ethylmaleimide > W complex > Mo complex > Fe complex. The X-ray structures of the adducts have been determined for M = W and Fe. DFT calculations on the starting complexes have been performed to explain the observed reactivity order.     

Substituted transition metal phospho olivines LiMM′PO4 (M = Mn,M′ = Fe,Co, Mg): Optimisation routes for LiMnPO4

Since transition metal phospho olivines gain increasing interest as cathode materials for lithium ion batteries in the last decades lots of publications appeared. Various synthesis methods were in the focus of interest as well as structural investigations of the pure LiMPO₄ and mixed Li (MM′)PO₄ phases (M, M′ = Fe, Mn, Co, Ni, Mg, Zn, Al) and their structural changes during electrochemical conversion. Lithium insertion and exsertion mechanisms have been studied with the help of e.g. structural, optical and electronic, and electrochemical characterisation methods. Likewise many efforts have been done for material optimisation concerning synthesis procedure or substitution.We tend to give an overview about Li (MM′Mn)PO₄ (M, M′ = Mg, Fe, Co) on the basis of our results. For the greater topic of enhancement of performance and energy density of LiMnPO₄ we discuss different solution approaches concerning the raise of specific capacity, redox potential and optimisation of material characteristics. Thus we consider effects due to the intrinsic conductivity, structural stability of the charged phase as well as its chemical stability against the electrolyte and the dynamic stability of the interface between charged phase and discharged phase during electrochemical conversion.For this purpose in our experimental part we focus on three different approaches: substitution with an electrochemically active transition metal, substitution with an electrochemically inactive metal in case for the manipulation of unit cell volume alternation and the substitution with electrochemically inactive metals for the purpose of providing a “lithium reservoir”. This generated “lithium reservoir” is expected to be accessible for the utilisation of a new redox step. Phase transition in mixed transition metal phospho olivines Li(MnCo)PO₄ has been investigated as example for the effect of substitution with an electrochemically active transition metal. Substitution with an electrochemically inactive metal leading to binary Li(MgMn)PO₄ has been structurally and electrochemically investigated. Promising new electrochemical characteristics of binary Li(MgMn)PO₄ phospho olivines are introduced for the first time. When charged to high potentials (>4.9 V) the activation of the Mn³⁺/Mn⁴⁺ step is reported.     

Energy decomposition analysis of the metal-imine bond in [(CO)4M–SB] (M = Cr,Mo, W; SB: RHCN–CH2CH2–NCHR)

The electronic and molecular structures of the metal-Schiff base complexes [(CO)₄M–SB] (M: Cr, Mo, W; SB: RHCN–CH₂CH₂–NCHR, R = C₆H₅, C₆F₅, Ortho-, Meta- and Para-XC₆H₄ (X = F, Cl, Br,CH₃)) have been investigated at the DFT level using the exchange correlation functional BP86. The nature of the TM?Schiff base interactions was analyzed with charge and energy decomposition methods. The octahedral equilibrium geometries have C_2v symmetry. The (CO)₄M–SB bond dissociation energies vary little for different substituents R. The calculated values indicate rather strong bonds which exhibit the trend for the different metals M = Mo (D_e = 59.8–65.4 kcal/mol) < Cr (D_e = 62.3–67.8 kcal/mol) < W (D_e = 69.9–75.8 kcal/mol). The energy decomposition analysis suggests that the (CO)₄M–SB attractive interactions come mainly from electrostatic attraction which provide ～60% to ?E_int while ～40% come from orbital interactions. The latter term arises mainly (～70%) through (CO)₄M ← SB σ donation from the nitrogen lone-pair orbitals while a much smaller part (～20%) comes from (CO)₄M→SB π backdonation. The transition metals carry large negative partial charges between ?2.3 e for M = Cr and ?1.1e for M = W.     

Studying (n, 0) and (m,m) GaP nanotubes (n = 3–10 and m = 2–6) through DFT calculations of Ga-69 quadrupole coupling constants

We investigated properties of representative zigzag and armchair gallium phosphide (GaP) nanotubes by performing density functional theory (DFT) calculations. To achieve our purpose, eight models of (n,0) zigzag GaP nanotubes with n = 3–10 and five models of (m,m) armchair GaP nanotubes m = 2–6 were considered. Each model was firstly optimized and quadrupole coupling constants (C_Q) were subsequently calculated for gallium-69 atoms of the optimized structures. The results indicated that the optimized properties including dipole moments, energy gaps, binding energies, and bond lengths could be mainly dependent on the diameters of GaP nanotubes, which are directly determined by n or m indices. Moreover, comparing the values of C_Q parameters indicated that the narrower GaP nanotubes could be considered as more reactive materials than the wider nanotubes, in which the reactivities are very important in determining the applications of nanotubes. And finally, the atoms at the sidewalls of nanotubes could be divided into atomic layers based on the similarities of properties for atoms of each layer, in which the properties of Ga atoms at the edges of nanotubes are significantly different from other layers only for wider nanotubes.     

Solubilities,densities and refractive indices for the ternary systems ethylene glycol + MCl + H2O (M = Na,K, Rb,Cs) at (15 and 35) °C

The solubilities, densities and refractive indices data for the four ternary systems ethylene glycol + MCl + H₂O (M = Na, K, Rb, Cs) at different temperatures were measured, with mass fractions of ethylene glycol in the range of 0 to 1.0. In all cases, the presence of ethylene glycol significantly reduces the solubility of the salts in aqueous solution. The experimental data of density, refractive index and solubility of saturated solutions for these systems were correlated using polynomial equations as a function of the mass fraction of ethylene glycol. On the other hand, the refractive index and density of unsaturated solutions was also determined for the four ternary systems with varied unsaturated salt concentrations. Values for both the properties were correlated with the salt concentrations and proportions of ethylene glycol in the solutions.     

Phosphasilaallenes >Si = C = P− and phosphagermaallenes >Ge = C = P−

Phosphasilaallene Tip(Ph)Si = C = PMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) and phosphagermaallene Mes₂Ge = C = PMes* (Mes = 2,4,6-trimethylphenyl) have been obtained by dehalogenation of their corresponding dihalophosphametallapropenes > E(X)-C(X′) = P? by tert-butyllithium. They dimerize above ?40 °C by a cycloaddition involving two E = C double bonds or the E = C and the P = C double bonds but can be characterized at low temperature by trapping reactions and by low field shifts in ³¹P, ²⁹Si and particularly ¹³C NMR for the sp carbon atom. Owing to a small increase in the steric hindrance, phosphagermaallene Tip(t-Bu)Ge = C = PMes* can be stabilized and isolated. The Ge = C double bond undergoes nearly quantitative [2 + 1] cycloadditions with chalcogens and [2 + 2] cycloadditions with aldehydes or ketones. The surprisingly stable lithiochlorosilane R(Cl₂)Si-C(Li) = PMes* (R = 9-methylfluorenyl) behaves as a synthetic equivalent of the phosphasilaallene R(Cl)Si = C = PMes*. With two alkyl groups (t-Bu) on the germanium atom, the phosphagermaallene t-Bu₂Ge = C = PMes* is not obtained but its formal dimers 1,3-digermacyclobutanes have been isolated.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.     

The structural and thermal stability,electrochemical hydrogenation and corrosion behavior of LaT5−xMx(T = Co,Ni and M = Al,Ge, Li) phases

The structural and thermal stability, electrochemical hydrogenation and corrosion behavior of LaT_5−x(M/Li)_x (T = Co, Ni and M = Al, Ge) alloys have been investigated using x-ray diffraction, SEM with WDS/EDX, DSC and electrochemical techniques. The prepared ternary and quaternary samples are solid solutions on the base of binary LaCo₅ and LaNi₅ compounds with hexagonal CaCu₅ structure type. By partial substitution of transition metals (Ni and Co) by Al, Ge and Li in the LaT_5−x(M/Li)_x alloys the discharge capacity increased by 25%. Doping of LaCo₅ and LaNi₅ binary phases by Al, Ge and Li improves corrosion resistance, thermal stability and absorption capacity during the electrochemical hydrogenation. These alloys passivate effectively in strong alkaline solution.     

Electronic structure of lanthanum transition-metal oxyarsenides LaMAsO (M = Fe,Co, Ni) and LaFe1−xM′xAsO (M′ = Co,Ni) by X-ray photoelectron and absorption spectroscopy

The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p_3/2 and arsenic 3d_5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M²⁺ and As^3?) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d_5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La³⁺O^2?][M²⁺As^3?]. The mixed-metal series LaFe_1?xM′_xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place.     

Spin-glass state in Ni5(OH)6(CnH2n−4O4)2 metal-organic frameworks (n = 6, 8, 10, 12)

We present an extension of a previously published work (J. Solid State Chem. 181 (2008) 3229) concerning Metal-Organic Frameworks (MOFs) of general formula Ni₅(OH)₆(C_nH_2n−4O₄)₂. A modified synthesis procedure comprising a room-temperature step prior to the hydrothermal treatment was employed. This preliminary step made use of peristaltic pumps allowing slow mixing of the reactants at a constant pH value. Samples of better purity and crystallinity were consequently obtained. In particular, the better crystallinity allowed us to work on two other members of the series, n = 10 and n = 12, which were characterized using synchrotron powder X-ray powder diffraction. These two compounds are isoreticular with the n = 6 and n = 8 compounds previously reported. The crystal structure incorporates the long alkane dioic acid molecules as pillars between complex inorganic layers. Samples of better purity for n = 6 and 8, as well as those of the new compounds with n = 10 and 12, gave us the opportunity to revise the magnetic properties of these MOFs. We found similar magnetic behaviors, independently of the interlayer spacing. We show that, below 19 K, these materials most probably enter a spin-glass or cluster spin-glass state rather than a three-dimensionally long-range ordered state. We link this behavior to the complex topology of the magnetic exchange interactions within the inorganic layers which is very likely to be source of magnetic frustration.