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.     

Protonation thermodynamics of some aminophenol derivatives in NaCl(aq) (0 ⩽ I ⩽3 mol · kg−1) at T = 298.15 K

The acid–base properties of four aminophenol derivatives, namely m-aminophenol (L1), 4-amino-2-hydroxytoluene (L2), 2-amino-5-ethylphenol (L3) and 5-amino-4-chloro-o-cresol (L4), are studied by potentiometric and titration calorimetric measurements in NaCl_(aq) (0 ? I ? 3 mol · kg^?1) at T = 298.15 K. The dependence of the protonation constants on ionic strength is modelled by the Debye–Hückel, SIT (Specific ion Interaction Theory) and Pitzer equations. Therefore, the values of protonation constants at infinite dilution and the relative interaction coefficients are calculated. The dependence of protonation enthalpies on ionic strength is also determined. Distribution (2-methyl-1-propanol/aqueous solution) measurements allowed us to determine the Setschenow coefficients and the activity coefficients of neutral species. Experimental results show that these compounds behave in a very similar way, and common class parameters are reported, in particular for the dependence on ionic strength of both protonation constants and protonation enthalpies.     

Interactions in (l-phenylalanine/l-histidine + 0.01 mol · kg−1 aqueous β-cyclodextrin) systems at T = (293.15, 298.15, 303.15 and 308.15) K

Densities (ρ) and speeds of sound (u) have been measured for (l-phenylalanine + 0.01 mol · kg⁻¹ aqueous β-cyclodextrin) and (l-histidine + 0.01 mol · kg⁻¹ aqueous β-cyclodextrin) systems at T = (293.15, 298.15, 303.15 and 308.15) K using the density and sound velocity Meter DSA 5000 M. The ρ and u values have been utilized to evaluate values of the partial molar volume (${\varphi }_v^{\circ }$), transfer partial molar volume (${\mathrm{\Delta }}_{\text{tr}}{\varphi }_v^{\circ }$), partial molar isentropic compressibility (${\varphi }_k^{\circ }$), and transfer partial molar isentropic compressibility (${\mathrm{\Delta }}_{\text{tr}}{\varphi }_k^{\circ }$) of the systems studied. The experimentally measured and calculated parameters have been interpreted in terms of host-guest and ion-hydrophilic interactions operative in the systems.     

Planar tetracoordinate carbon in CE42− (E = Al–Tl) clusters

The structures and bonding of the CE₄^2?clusters (E = Al, Ga, In, Tl) have been theoretically studied via B3LYP/def2-TZVP computations. Total energies were recalculated at the CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level in order to corroborate the energy differences. Our computations show that all the CE₄^2?and CE₄Li^?clusters (E = Al, Ga, In,Tl) have a planar tetracoordinate carbon structure. Interestingly, while the most stable form of CAl₄Li^? and CGa₄Li^? is planar with coordination of Li⁺ to an edge of the CE₄^2? fragment, for CIn₄Li^? and CTl₄Li^? the pyramidal structures with C_4v symmetry are the lowest-energy structures.     

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.     

Synthesis,characterization and reactions of the transition metal halogenoalkyl carbocation complexes [Cp(CO)2M{η2-CH2CH(CH2)nX}]PF6 (n = 1–8, 10, M = Fe; n = 3, 4 M = Ru; X = Br,I)

The halogenoalkyl complexes [Cp(CO)₂M{(CH₂)_nX}] (n = 3–10, 12, M = Fe; n = 5, 6, M = Ru, X = Br, I) react with Ph₃CPF₆ in dry CH₂Cl₂ to give the corresponding carbocation complexes [Cp(CO)₂M{η²-(CH₂CH(CH₂)_n?2X}]PF₆ in high yields. NMR evidence indicates that the metals form metallacyclopropane type structures with the carbocation ligand. The reactions of some of the cationic complexes with NaI, PPh₃, Na[Cp(CO)₂Fe] and Et₃N are discussed. NaI and Na[Cp(CO)₂Fe] displace the halogeno-olefin, while PPh₃ adds at the β-CH^δ+ giving the unstable phosphonium adducts [Cp(CO)₂Fe{CH₂CH(PPh₃)(CH₂)_n?2X}]PF₆ which decompose to the halogeno-olefins and the cationic PPh₃ complex [Cp(CO)₂Fe(PPh₃)]⁺. Et₃N causes allylic deprotonation forming internal olefin complexes of the type [Cp(CO)₂Fe{CH₂CHCH(CH₂)_n?3X}]PF₆.     

The enthalpies of formation of BaCe1−xRExO3−δ (RE = Eu,Tb, Gd)

The preparation of BaCeO₃ doped by gadolinium, europium, and terbium oxides (BaCe_0.8Eu_0.1Tb_0.1O_2.9 and BaCe_0.8Gd_0.2O_2.9) has been performed by solid-state reaction from BaCO₃, CeO₂, Gd₂O₃, Eu₂O₃, Tb₄O₇. The X-ray measurements have showed that BaCe_0.8RE_0.2O_2.9 (RE = Gd, Eu, Tb) was orthorhombic structure (space group Pnma). The standard formation enthalpies of BaCe_0.8Eu_0.1Tb_0.1O_2.9 and BaCe_0.8Gd_0.2O_2.9 have been determined by solution calorimetry combining the solution enthalpies of BaCe_0.8Gd_0.2O_2.9 (BaCe_0.8Eu_0.1Tb_0.1O_2.9) and BaCl₂ + 0.8CeCl₃ + 0.2GdCl₃ (BaCl₂ + 0.8CeCl₃ + 0.1EuCl₃ + 0.1TbCl₃) mixtures in 1 M HCl with 0.1 M KI at T = 298.15 K and literature data.     

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.     

On the physical properties of Sr1−xNaxRuO3 (x = 0–0.19)

The metallic ferromagnetic perovskite-type SrRuO₃ (T_C ～ 160 K) belongs to the “class” of materials with strongly correlated electrons. Nonetheless a simple ferromagnetism associated with isotropic interactions of low spin Ru⁴⁺ ions local moments is far too simple to explain the complex interplay between charge carriers and magnetic interactions. In that sense the suppression of ferromagnetism in isoelectronic Sr_1?xCa_xRuO₃ was tentatively associated to the increased lattice distortion influencing primarily the 4d Ru bandwidths and, hence, the itinerancy and respective populations of the spin-up and spin-down electrons.In order to probe the robustness of the metallic ferromagnetism against electron occupation of 4d Ru orbital we prepared and characterized polycrystalline Sr_1?xNa_xRuO₃ (x = 0.0–0.19) ceramics. The substitution of Sr²⁺ by Na¹⁺, leading to formally mixed valence Ru⁴⁺/Ru⁵⁺, induces the decrease of the Curie temperature and spin-wave stiffness, which was determined independently from magnetic and specific heat data. On the other hand the effective paramagnetic moment remains essentially unchanged. All compounds are metallic in a sense of electrical resistivity and thermopower temperature dependence; the low temperature upturn of the electrical resistivity was explained on a base of the weak localization. The metallic nature of the samples is corroborated by Pauli paramagnetism and high Sommerfeld coefficient γ, extracted from the low temperature specific heat, which increases from 30.9 mJ mol^?1 K^?2 (x = 0.0) to 43.0 mJ mol^?1 K^?2 (x = 0.19).     

The oxygen deficient cubic perovskite SrFe1−xScxO3−δ (x ≤ 0.5; 0.1 ≤ δ ≤ 0.5): Structural features and physical properties

Solid state synthesis method has been used to stabilize oxygen deficient perovskite phases SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5). The good homogeneity of samples is confirmed by energy dispersive spectroscopy (EDS) analysis performed with a transmission electronic microscope (TEM). By combining X-ray and electronic diffraction (ED), it is demonstrated that the cationic substitution on the B site of the perovskite induces a decrease of the oxygen content but without inducing long range ordering phenomenon. On this basis, X-ray patterns of compounds were indexed in the cubic Pm3m space group. The oxidation states of iron evidenced by Mössbauer spectroscopy, are in good agreement with the oxygen stoichiometries determined by cerimetric titration. In the SrFe_1?xSc_xO_3?δ series, the Fe³⁺/Fe⁴⁺ origin of the electronic conductivity is clearly evidenced. The limit compound SrFe_0.5Sc_0.5O_2.5 is highly resistive and characterized by a cluster glass-like behaviour. Finally, negative magnetoresistivity properties are revealed for the x = 0.1 and x = 0.2 samples, reaching ?10% around the magnetic transition temperature in a 7T magnetic field.     

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.     

Crystal structure of the Fe6−xGayGe5−y (x ∼0.5, y = 1.3) ternary compound

The single crystal of Fe_6−xGa_yGe_5−y (x ∼0.5, y = 1.3(1)) has been obtained from arc-melting of the elements and its crystal structure has been investigated by single-crystal X-ray diffraction analysis. The compound crystallizes in the hexagonal space group P6₃/mmc (No. 194) with a = 8.0346(2) Å, c = 5.007(1) Å, Z = 1 and adopts the Ti₆Sn₅ structure type with a refined composition of Fe_5.52(12)(Ga/Ge)₅. By a mean of scanning electron microscopy the composition of the single crystal has been determined as Fe_4.9(2)Ga_1.3(1)Ge_3.7(1). The crystal structures of the Fe_6−xGa_yGe_5−y (x ∼0.5, y = 1.3(1)) and all compounds in the Fe–Ge binary system have been crystallographically analyzed and structural relationship has been established.     

Thermodynamic properties of tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate fromT → 0 toT = 340 K

The temperature dependence of the standard molar heat capacity C_{p, m}^oof samples of crystalline tetraphenylphosphonium perchlorate and tetraphenylarsonium perchlorate was measured in an adiabatic low-pressure calorimeter between T =  4.8 K and T =  340 K and from T =  5.8 K to T =  340 K, respectively, mostly to within a precision of 0.2 per cent. For tetraphenylphosphonium perchlorate, an anomalous change of the heat capacity in the range T =  125 K to T =  185 K, probably arising from the excitation of hindered rotations of atomic groups, was found and its thermodynamic characteristics were determined. No such anomaly was observed for tetraphenylarsonium perchlorate. The data obtained were used to calculate the thermodynamic functions C_{p, m}^o(T) / R, Δ₀^TH_m^o / R·K, Δ₀^TS_m^o / R, and Φ_m^o = Δ₀^TS_m^o − Δ₀^TH_m^o / T(where R is the universal gas constant) of the compounds between T →  0 and T =  340 K.     

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.     

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.