Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Competition between non-classical and classical hydrogen bonded sites in [BH3CN]: Spectral, energetic, structural and electronic features

Interaction of the salt (Ph₃PNPPh₃)BH₃CN with the various OH and NH proton donors in low polar media was studied by variable temperature (200–290 K) IR spectroscopy and theoretically by DFT calculations. The formation of two types of complexes containing non-classical dihydrogen bond to the hydride hydrogen (DHB) and classical hydrogen bond (HB) to nitrogen lone pair was shown in solution. The 1:1 complexes of both types (XHH and XHN) coexist in the presence of equimolar amount of proton donor. The addition of excess XH-acid leads to the increase of the classical HB content and appearance of the 1:2 complexes, where two basic sites work simultaneously. The structure, spectral characteristics, energy and electron redistribution were studied by DFT (B3LYP) method. The comparison DHB parameters of [BH₃CN]⁻ with those of the unsubstituted analogue [BH₄]⁻ allowed analyzing the electronic effects of the CN group on the basic properties of boron hydride moiety. The electronic influence of the BH₃ group on CN⁻HX hydrogen bond was also established by comparison with the corresponding classical HB to the CN⁻ anion.     

Hydrogen bond strength in chromates with kröhnkite-type chains, K2Me(CrO4)2·2H2O (Me = Mg, Co, Ni, Zn, Cd)

Infrared spectra of the title compounds with kröhnkite-type infinite octahedral–tetrahedral chains, K₂Me(CrO₄)₂·2H₂O (Me = Mg, Co, Ni, Zn, Cd), are presented in the regions of the uncoupled O–D stretching modes of matrix-isolated HDO molecules (isotopically dilute samples) and water librations. The strengths of the hydrogen bonds are discussed in terms of the respective O_wO bond distances, the Me–water interactions (synergetic effect), the proton acceptor capability of the chromate oxygen atoms as deduced from Brown's bond valence sum of the oxygen atoms. The spectroscopic experiments reveal that hydrogen bonds of medium strength are formed in the chromates. The hydrogen bond strengths decrease in the order Cd > Zn > Ni > Co in agreement with the decreasing covalency of the respective Me–OH₂ bonds in the same order, i.e. decreasing acidity of the water molecules. The infrared band positions corresponding to the water librations confirm the claim that the hydrogen bonds in K₂Cd(CrO₄)₂·2H₂O are stronger than those formed in K₂Mg(CrO₄)₂·2H₂O on one hand, and on the other—the hydrogen bonds in K₂Ni(CrO₄)₂·2H₂O are stronger than those in K₂Co(CrO₄)₂·2H₂O.     

Fermi resonance and strong anharmonic effects in the absorption spectra of the ν-OH (ν-OD) vibration of solid H- and D-benzoic acid

The vibrational spectra of polycrystalline benzoic acid (BA) and its deuterated derivative were studied over the wide frequency region 4000–10 cm⁻¹ by IR and Raman methods. A theoretical analysis of the hydrogen bond frequency region and calculations at the B3LYP/6-311++G(2d, 2p) level for the benzoic acid cyclic dimer in the gas phase were made. In order to study the dynamics of proton transfer two formalisms were applied: Car–Parrinello Molecular Dynamics (CPMD) and Path Integrals Molecular Dynamics (PIMD). It was shown that the experimentally observed very broad ν-OH band absorption is the result of complex anharmonic interaction: Fermi resonance between the OH-stretching and bending vibrations and strong interaction of the ν-OH stretching with the low frequency phonons. The theoretical analysis in the framework of such an approach gave a good correlation with experiment. From the CPMD calculations it was confirmed that the O–HO bridge is not rigid, with the OO distance being described by a large amplitude motion. For the benzoic acid dimer we observed stepwise (asynchronous) proton transfer.     

Heat capacity, enthalpy and entropy of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7

The heat capacity and the enthalpy increments of strontium niobate Sr₂Nb₂O₇ and calcium niobate Ca₂Nb₂O₇ were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (720–1370 K). Temperature dependencies of the molar heat capacity in the form C_pm = 248.0 + 0.04350T − 3.948 × 10⁶/T² J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and C_pm = 257.2 + 0.03621T − 4.434 × 10⁶/T² J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇ were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, S_m°(298.15 K) = 238.5 ± 1.3 J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and S_m°(298.15 K) = 212.4 ± 1.2 J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇, were evaluated from the low-temperature heat capacity measurements.     

Theoretical study of the reaction of CF3O radicals with CO

The potential energy surface for the reaction of the CF₃O radicals with CO was investigated. The geometries and vibrational frequencies of the reactants, transition states, intermediates, and products were calculated at the UB3LYP/6-311+G(2d,p), UB3LYP/6-311+G(3df,2p) and UMP2/6-311+G(2d,p) levels of theory. The energies were improved by using the G2M(CC2) and G3B3 methods. The calculation suggests the reaction proceeds via either the fluorine abstraction of CF₃O by CO to produce FCO + CF₂O with a high energy barrier or the barrierless association of the reactants to form the trans-CF₃OCO intermediate. The trans-CF₃OCO is predicted to undergo subsequent isomerization to cis-CF₃OCO or dissociate directly to the products FCO + CF₂O and CF₃ + CO₂. The collisional stabilization of trans-CF₃OCO is dominant at room temperature, while trans-CF₃OCO isomerizing to cis-CF₃OCO followed by dissociating to CF₃ + CO₂ is accessible when temperature rises. The reason for only trans-CF₃OCO without cis-CF₃OCO observable in Ashen’s experiment [S.V. Ahsen, J. Hufen, H. Willner, J.S. Francisco, Chem. Eur. J. 8 (2002) 1189] is cis-CF₃OCO can be produced only via the isomerization of trans-CF₃OCO, and its yield is inappreciable at a low experimental temperature. The enthalpies of formation for the two conformations of CF₃OCO have been deduced: (trans-CF₃OCO) = −196.25 kcal mol⁻¹, (trans-CF₃OCO) = −197.46 kcal mol⁻¹, (cis-CF₃OCO) = −193.64 kcal mol⁻¹, and (cis-CF₃OCO) = −194.90 kcal mol⁻¹.     

Ba2In2O4(OH)2: Proton sites, disorder and vibrational properties

The structure of Ba₂In₂O₄(OH)₂ is analysed by the explicit full optimization of a large number of possible proton arrangements using periodic density functional theory. It is shown that the experimental assignments in which protons appear to be located at high symmetry positions with unphysical bond lengths do not correspond to minima on the potential energy hypersurface. The apparent sites are averages of a number of possible proton locations involving a set of possible local structural environments in which the internuclear separations are more realistic. Such problems with structural refinements are common where profile refinement programs place the atoms at the average position due to dynamic and/or static disorder. Thus while the calculations support a previous neutron diffraction analysis of the structure in that the average structure contains two different proton sites, they also reveal substantial information about the local environments of the protons. In all optimizations, the protons moved from the average positions suggested in the neutron diffraction study with calculated O–H and OHO distances consistent with those observed in other oxides. The energies of different proton distributions vary significantly so the protons are not randomly distributed. We also present an analysis of the vibrational properties of the O–H bonds. Since the strength of the hydrogen bonds is closely related to the local structural environments of the protons, a range of vibrational frequencies is obtained providing a prediction of the vibrational spectra. In O–HO linkages, O–H stretching modes soften with increasing HO hydrogen bond strength, while the in-plane and out-of-plane bending or libration modes stiffen. Together, our results show how modern theoretical methods can provide a clearer understanding of the structure and dynamics of a complex inorganic material.     

Effect of chelating agent on the oxidation rate of PCP in the magnetite/H2O2 system at neutral pH

The complex [Rh(CO)₂Cl]₂ reacts with two molar equivalent of pyridine carboxylic acids ligands Py-2-COOH(a), Py-3-COOH(b) and Py-4-COOH(c) to yield rhodium(I) dicarbonyl chelate complex [Rh(CO)₂(L^/)](1a) {L^/ = η²-(N,O) coordinated Py-2-COO⁻(a^/)} and non-chelate complexes [Rh(CO)₂ClL^//](1b,c) {L^// = η¹-(N) coordinated Py-3-COOH(b), Py-4-COOH(c)}. The complexes 1 undergo oxidative addition (OA) reactions with different electrophiles such as CH₃I, C₂H₅I, C₆H₅CH₂Cl and I₂ to give penta coordinated Rh(III) complexes of the types [Rh(CO)(CORⁿ)XL^/], {n = 1,2,3; R¹ = CH₃(2a); R² = C₂H₅(3a); X = I and R³ = CH₂C₆H₅ (4a); X = Cl}, [Rh(CO)I₂L^/](5a), [Rh(CO)(CORⁿ)ClXL^//] {R¹ = CH₃(6b,c); R² = C₂H₅(7b,c); X = I and R³ = CH₂C₆H₅ (8b,c); X = Cl} and [Rh(CO)ClI₂L^//](9b,c). The complexes have been characterized by elemental analysis, IR and ¹H NMR spectroscopy. Kinetic data for the reaction of 1a–b with CH₃I indicate a first order reaction. The catalytic activity of 1a–c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 810–1094) is obtained compared with that of the well-known commercial species [Rh(CO)₂I₂]⁻ (TON = 653) at mild reaction conditions (temperature 130 ± 5 °C, pressure 35 ± 5 bar).     

Study of ion–solvent interactions of some tetraalkylammonium halides in THF + CCl4 mixtures by conductance measurements

Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen₄NCl), tetrahexylammonium chloride (Hex₄NCl), tetraheptylammonium chloride (Hep₄NCl), and tetraoctylammonium chloride (Oct₄NCl) were measured at 298.15 K in THF + CCl₄ mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M⁺ + X⁻ ↔ MX, K_P) and triple-ions (2M⁺ + X⁻ ↔ M₂X⁺; M⁺ + 2X⁻ ↔ MX₂⁻, K_T). A linear relationship between the triple-ion formation constants [log(K_T/K_P)] and the salt concentrations at the minimum conductivity (log C_min) was given for all salts in THF + CCl₄ mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R₄N⁺X⁻).     

Conformational analysis of 2-halocyclopentanones by NMR and IR spectroscopies and theoretical calculations

The conformational isomerism of 2-chlorocyclopentanone and 2-bromocyclopentanone has been determined through the solvent dependence of the ¹H NMR ³J_HH coupling constants, theoretical calculations and infrared data, using the solvation theory for the treatment of NMR data. In 2-chlorocyclopentanone, the energy difference (E_Ψ-e − E_Ψ-a), in the isolated molecule at B3LYP level of theory, between the pseudo-equatorial (Ψ-e) and pseudo-axial (Ψ-a) conformers is 0.42 kcal mol⁻¹, which decreases in CCl₄ and in acetonitrile solutions, in good agreement with infrared data (ν_CO), despite the uncertainties of the latter method. The conformational equilibrium for 2-bromocyclopentanone is also between the Ψ-e and Ψ-a conformations, with an energy difference (E_Ψ-e − E_Ψ-a), in the isolated molecule at B3LYP level of theory, is 0.85 kcal mol⁻¹ which decreases in CCl₄ and in acetonitrile solutions, also in good agreement with infrared data.     

Fabrication of mesoporous SiO2–C–Fe3O4/γ–Fe2O3 and SiO2–C–Fe magnetic composites

A synthetic method for the fabrication of silica-based mesoporous magnetic (Fe or iron oxide spinel) nanocomposites with enhanced adsorption and magnetic capabilities is presented. The successful in situ synthesis of magnetic nanoparticles is a consequence of the incorporation of a small amount of carbon into the pores of the silica, this step being essential for the generation of relatively large iron oxide magnetic nanocrystals (10 ± 3 nm) and for the formation of iron nanoparticles. These composites combine good magnetic properties (superparamagnetic behaviour in the case of SiO₂–C–Fe₃O₄/γ–Fe₂O₃ samples) with a large and accessible porosity made up of wide mesopores (>9 nm). In the present work, we have demonstrated the usefulness of this kind of composite for the adsorption of a globular protein (hemoglobin). The results obtained show that a significant amount of hemoglobin can be immobilized within the pores of these materials (up to 180 mg g⁻¹ for some of the samples). Moreover, we have proved that the composite loaded with hemoglobin can be easily manipulated by means of an external magnetic field.     

Glass–ceramic Li2S–P2S5 electrolytes prepared by a single step ball billing process and their application for all-solid-state lithium–ion batteries

We report that glass–ceramic Li₂S–P₂S₅ electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi₂S·(100 − x)P₂S₅ system at 55 °C produced crystalline glass–ceramic materials exhibiting high Li-ion conductivity over 10⁻³ S cm⁻¹ at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass–ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability.     

Theoretical study on the structures and properties of the isomers of Nn(CH)8−nH8 (n = 0–7)

With replacement of N atoms by CH groups in the most stable chain isomer of N8H8, 34 possible isomers of N_n(CH)_8−nH₈ (n = 0–7) have been designed and optimized at the B3LYP/6-311++G** level of theory. The natural bond orbital (NBO) and atoms in molecules (AIM) analysis are carried out to study the bonding nature and relative stabilities of these conformers. G3MP2 method is applied to calculate energies and heats of formation. The results indicate that the hyperconjugation effect from lone pairs of nitrogen atoms to germinal C–N bonds is the major factor which caused the change of the C–N bond length. With the more replacement of nitrogen atoms by CH groups, the heats of formation of the isomers of N_n(CH)_8−nH₈ (n = 0–7) decrease gradually, but the energies increase linearly.     

Vibrational satellite of Na(3d ← 3s) dipole-forbidden transition in Na/CF4 mixture

Excitation spectra of Na fluorescence in mixtures with CF₄ display a new band shifted by the energy of one-vibrational quantum of the IR active ν₃-mode of CF₄ (1281 cm⁻¹) from Na 3d states. This band is attributed to a Na(3s)CF₄(ν₃ = 0) → Na(3d)CF₄(ν₃ = 1) transition and its intensity is explained by coupling with Na(4p)CF₄(v₃ = 0) resonance state which lies  180 cm⁻¹ below in energy. An analogous satellite of the Na 6p state combined with the same vibration and lying close to the Na 7p state is reported and discussed.     

Protonated MF3 (M = N-Bi): Structure, stability, and thermochemistry of the H-MF3 and HF-MF2 isomers

The structure, stability, and thermochemistry of the H(MF₃)⁺ isomers (M = N-Bi) have been investigated by MP2 and coupled cluster calculations. All the HF-MF₂⁺ revealed weakly bound ion-dipole complexes between MF₂⁺ and HF. For M = N, As, Sb, and Bi they are more stable than the H-MF₃⁺ covalent structures (free energy differences) by 6.3, 14.3, 32.1, and 73.5 kcal mol⁻¹, respectively. H-PF₃⁺ is instead more stable than HF-PF₂⁺ by 21.8 kcal mol⁻¹. The proton affinities (PAs) of MF₃ at the M atom range from 91.9 kcal mol⁻¹ (M = Bi) to 156.5 kcal mol⁻¹ (M = P), and follow the irregular periodic trend BiF₃ < SbF₃ < AsF₃ < NF₃ < PF₃. The PAs at the F atom range instead from 131.9 kcal mol⁻¹ (M = P) to 164.9 kcal mol⁻¹ (M = Bi), and increase in the more regular order PF₃ ≈ NF₃ < AsF₃ < SbF₃ < BiF₃. This trend parallels the fluoride-ion affinities of the MF₂⁺ cations. For protonated NF₃ and PF₃, the calculations are in good agreement with the available experimental results. As for protonated AsF₃, they support the formation of HF-AsF₂⁺ rather than the previously proposed H-AsF₃⁺. The calculations indicate also that the still elusive H(SbF₃)⁺ and H(BiF₃)⁺ should be viable species in the gas phase, exothermically obtainable by various protonating agents.     

Mechanism and kinetics of crystallization of α-Fe in amorphous Fe81B13Si4C2 alloy

The non-isothermal crystallization of α-Fe from Fe₈₁B₁₃Si₄C₂ amorphous alloy was investigated. The kinetic parameters of crystallization process were determined by Kissinger and Kissinger–Akahira–Sunose (KAS) methods. It was established that the kinetic parameters of transformation do not change with the degree of crystallization in the range of 0.1–0.7. The kinetic model of the crystallization process was determined using the Malek's procedure. It was established that the primary crystallization α-Fe phase from amorphous alloy can be described by Šesták–Berggren autocatalytic model with kinetic triplet E_a = 349.4.0 kJ mol⁻¹, ln A = 50.76 and f(α) = α^0.72(1 − α)^1.02.     

DFT study on the intermolecular interactions between Aun (n = 2–4) and thymine

Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H₂O)_n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H₂O, nine steady luteolin–(H₂O)₂ and ten steady luteolin–(H₂O)₃, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H₂O)_n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.     

Ethylene addition to OsO3(CH2) - A theoretical study

Quantum chemical calculations at the B3LYP/TZVP level of theory have been carried out for the initial steps of the addition reaction of ethylene to OsO₃(CH₂). The calculations predict that there are two reaction channels with low activation barriers. The kinetically and thermodynamically most favored reaction is the [3+2]_O, C addition which has a barrier of only 2.3 kcal mol⁻¹. The [3+2]_O, O addition has a slightly higher barrier of 6.5 kcal mol⁻¹. Four other reactions of OsO₃(CH₂) with C₂H₄ have significantly larger activation barriers. The addition of ethylene to one oxo group with concomitant migration of one hydrogen atom from ethylene to the methylene ligand yields thermodynamically stable products but the activation energies for the reactions are 16.7 and 20.9 kcal mol⁻¹. Even higher barriers are calculated for the [2+2] addition to the OsO bond (32.6 kcal mol⁻¹) and for the addition to the oxygen atom yielding an oxiran complex (41.2 kcal mol⁻¹). The activation barriers for the rearrangement to the bisoxoosmaoxirane isomer (36.3 kcal mol⁻¹) and for the addition reactions of the latter with C₂H₄ are also quite high. The most favorable reactions of the cyclic isomer are the slightly exothermic [2+2] addition across the OsO bond which has an activation barrier of 46.6 kcal mol⁻¹ and the [3+2]_O, O addition which is an endothermic process with an activation barrier of 44.3 kcal mol⁻¹.     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

Kinetics of adsorption of Saccharomyces cerevisiae mandelated dehydrogenase on magnetic Fe3O4–chitosan nanoparticles

The adsorption of Saccharomyces cerevisiae mandelated dehydrogenase (SCMD) protein on the surface-modified magnetic nanoparticles coated with chitosan was studied in a batch adsorption system. Functionalization of surface-modified magnetic particles was performed by the covalent binding of chitosan onto the surface of magnetic Fe₃O₄ nanoparticles. Characterization of these particles was carried out using FTIR spectra, transmission electron micrography (TEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Magnetic measurement revealed that the magnetic Fe₃O₄–chitosan nanoparticles were superparamagnetic and the saturation magnetization was about 37.3 emu g⁻¹. The adsorption capacities and rates of SCMD protein onto the magnetic Fe₃O₄–chitosan nanoparticles were evaluated. The adsorption capacity was influenced by pH, and it reached a maximum value around pH 8.0. The adsorption capacity increased with the increase in temperature. The adsorption isothermal data could be well interpreted by the Freundlich isotherm model. The kinetic experimental data properly correlated with the first-order kinetic model, which indicated that the reaction is the adsorption control step. The apparent adsorption activation energy was 27.62 kJ mol⁻¹ and the first-order constant for SCMD protein was 0.01254 min⁻¹ at 293 K.