Thermochemistry of Complex Formation of Endofullerene Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> with the Triflate Ion

The density functional theory method at the M06-2X/6-31G(d,p) level was used to calculate the optimal geometry and thermodynamic parameters of formation of the Li⁺CF₃SO₃^? and Li⁺@C₆₀(CF₃SO₃^?) ion pairs, as well as topological characteristics of the electron density distribution in the critical point (3,?1) of bonds between lithium cation endofullerene Li⁺@C₆₀, and the triflate anion in a vacuum and in chlorobenzene.     

Synthesis of endohedral di-and monometallofullerenes Y<Subscript>2</Subscript>@C<Subscript>84</Subscript>, Ce<Subscript>2</Subscript>@C<Subscript>78</Subscript>, and M@C<Subscript>82</Subscript> (M = Y,Ce)

Endohedral metallofullerenes Y₂@C₈₄, Ce₂@C₇₈, and M@C₈₂ (M = Y, Ce) were synthesized by the electric arc method and isolated from the soot using extraction with o-dichlorobenzene. Pure (98%) endohedral dimetallofullerenes Y₂@C₈₄ and Ce₂@C₇₈ were isolated for the first time from o-dichlorobenzene extracts using HPLC and characterized by mass spectrometry and spectrophotometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2067–2071, November, 2007.     

Endohedral Complex of Fullerene C<Subscript>60</Subscript> with Tetrahedral N<Subscript>4</Subscript>, N<Subscript>4</Subscript>@C<Subscript>60</Subscript>

B3LYP/6-31G(d) hybrid HF/DFT and BLYP/6-31G(d, p) DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C₆₀ with Tetrahedral N₄ (T_d N₄), N₄@C₆₀. It was demonstrated that N₄ was seated in the center of the fullerene cage and the tetrahedral structure of N₄ is remained in the cage. The formation of this complex is endothermic with inclusion energy of 37.92 kcal/mol. N₄ endohedral doping perturbs the molecular orbitals of C₆₀ not so much, the calculated HOMO–LUMO gaps, the electron affinity (EA) and the ionizational potential (IP) of N₄@C₆₀ are similar to that of C₆₀.     

Bingel–Hirsch Addition of Diethyl Bromomalonate to Ion-Encapsulated Fullerenes M@C60 (M=Ø, Li+, Na+, K+, Mg2+, Ca2+, and Cl−)

In the last 30 years, fullerene-based materials have become popular building blocks for devices with a broad range of applications. Among fullerene derivatives, endohedral metallofullerenes (EMFs, M@C_x) have been widely studied owing to their unique properties and reactivity. For real applications, fullerenes and EMFs must be exohedrally functionalized. It has been shown that encapsulated metal cations facilitate the Diels–Alder reaction in fullerenes. Herein, the Bingel–Hirsch (BH) addition of ethyl bromomalonate over a series of ion-encapsulated M@C₆₀ (M=Ø, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cl⁻; Ø@C₆₀ stands for C₆₀ without any endohedral metal) is quantum mechanically explored to analyze the effect of these ions on the BH addition. The results show that the incarcerated ion has a very important effect on the kinetics and thermodynamics of this reaction. Among the systems studied, K⁺@C₆₀ is the one that leads to the fastest BH reaction, whereas the slowest reaction is given by Cl⁻@C₆₀.     

Initiation of ethylene polymerization on organoelement cations L<Subscript>2</Subscript>MMe<Superscript>+</Superscript> (M = Ge,Sn) with intramolecular coordination bonds: a theoretical study

The initiation of ethylene polymerization on L₂MMe⁺ cations (M = Ge, Sn; L = alkoxy, alkyl, phenoxyiminate, β-diketonate) was studied by the PBE/TZ2P density functional method. It was found that ethylene insertion into the M—C bond of the L₂MMe⁺ cations is energetically favorable (ΔG ⁰ = −7.6—−13.6 kcal mol⁻¹). The calculated energy barriers to reactions lie in a wide range 39.8 to 75.6 kcal mol⁻¹. The lowest energy barriers were obtained for tin cations bearing hexa- and heptafluoroacetylacetonate substituents. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1338–1347, July, 2008.     

Osmotic Coefficients of the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=273.15 K

Osmotic coefficients and water activities for the Li₂B₄O₇+LiCl+H₂O system have been measured at T=273.15 K by the isopiestic method, using an improved apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined. φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq), and φ _E is based on equilibrium molalities from consideration of the equilibrium speciation into H₃BO₃,B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constants K _m for the aqueous speciation reactions were estimated. Two types of representations of the osmotic coefficients for the Li₂B₄O₇+LiCl+H₂O system are presented with ion-interaction models based on Pitzer’s equations with minor modifications: model (I) represents the φ _S data with six parameters based on considering the ion-interactions between three ionic species of Li⁺, Cl⁻, and B₄O₇²⁻, and model (II) for represents the φ _E data based on considering the equilibrium speciation. The parameters of models (I) and (II) are presented. The standard deviations for the two models are 0.0152 and 0.0298, respectively. Model (I) was more satisfactory than model (II) for representing the isopiestic data.     

Electronic spectra of C<Subscript>6</Subscript>H<Superscript>+</Superscript> and C<Subscript>6</Subscript>H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> in the gas phase

Measurement of the ³Π-³Π transition of C₆H⁺ in the gas phase near 19486 cm⁻¹ is reported. The experiment was carried out with a supersonic slit-jet expansion discharge using cavity ringdown absorption spectroscopy. Partly resolved P lines and observation of band heads permitted a rotational contour fit. Spectroscopic constants in the ground and excited-state were determined. The density of ions being sampled is merely 2×10⁸ cm⁻³. Broadening of the spectral lines indicates the excited-state lifetime to be ≈100 ps. The electronic transition of HC₆H₂⁺ at 26402 cm⁻¹ assumed to be ¹A₁-X¹A₁ in C_2v symmetry could not be rotationally resolved.     

Impact of environmental conditions on the sorption behavior of radionuclide <Superscript>60</Superscript>Co(II) on MnO<Subscript>2</Subscript>

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The removal of ⁶⁰Co(II) from wastewaters by MnO₂ was studied as a function of various environmental parameters such as shaking time, pH, ionic strength, foreign ions, and humic substances under ambient conditions. The results indicated that the sorption of ⁶⁰Co(II) on MnO₂ was strongly dependent on pH and ionic strength. At low pH, the sorption of ⁶⁰Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA/FA enhances ⁶⁰Co(II) sorption at low pH values, whereas reduces ⁶⁰Co(II) sorption at high pH values. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁰Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ⁶⁰Co(II) on MnO₂ was endothermic and spontaneous.     

Gas phase structure of micro-hydrated [Mn(ClO<Subscript>4</Subscript>)]<Superscript>+</Superscript> and [Mn<Subscript>2</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>3</Subscript>]<Superscript>+</Superscript> ions probed by infrared spectroscopy

Gas-phase infrared photodissociation spectroscopy is reported for the microsolvated [Mn(ClO₄)(H₂O) _n ]⁺ and [Mn₂(ClO₄)₃(H₂O) _n ]⁺ complexes from n = 2 to 5. Electrosprayed ions are isolated in an ion-trap where they are photodissociated. The 2600–3800 cm⁻¹ spectral region associated with the OH stretching mode is scanned with a relatively low-power infrared table-top laser, which is used in combination with a CO₂ laser to enhance the photofragmentation yield of these strongly bound ions. Hydrogen bonding is evidenced by a relatively broad band red-shifted from the free OH region. Band assignment based on quantum chemical calculations suggest that there is formation of water—perchlorate hydrogen bond within the first coordination shell of high-spin Mn(II). Although the observed spectral features are also compatible with the formation of structures with double-acceptor water in the second shell, these structures are found relatively high in energy compared with structures with all water directly bound to manganese. Using the highly intense IR beam of the free electron laser CLIO in the 800–1700 cm⁻¹, we were also able to characterize the coordination mode (η²) of perchlorate for two clusters. The comparison of experimental and calculated spectra suggests that the perchlorate Cl—O stretches are unexpectedly underestimated at the B3LYP level, while they are correctly described at the MP2 level allowing for spectral assignment.     

Effects of La<Superscript>3+</Superscript> on inward K<Superscript>+</Superscript> channels at plasma membrane in guard cells

The effects of La³⁺ on inward K⁺ channels at plasma membrane in vicia guard cells are investigated using the whole-cell patch-clamp recording mode. It is shown that La³⁺ on both sides of plasma membrane blocks inward K⁺ currents in a concentration-dependent manner, indicating that La³⁺ binding sites may exist on both sides of plasma membrane in guard cells in vicia. The dose response is fitted by the Michaelis-Menten relation characterized by an inhibitor constant K _i of 2.56±0.25 μmol · L⁻¹ (outside membrane) and (1.18±0.11)×10⁻¹⁵ mol · L⁻¹ (inside membrane). Intracellular La³⁺ has much stronger inhibitory effect on inward K⁺ currents than extracellular La³⁺ does, suggesting there may exist stronger binding sites inside membrane than outside membrane. Since ion channel activities of guard cells directly affect plant stomatal movement and water status, our results imply that rare earth elements might have potential practical values in regulating plant water status and strengthening plant drought endurance.     

Kinetic and equilibrium study of the deprotonation of 4-nitrophenyl[bis(ethylsulphonyl)]methane by organic bases in acetonitrile in the presence of common cation BH<Superscript>+</Superscript> and tetrabutylammonium perchlorate

The results of kinetic and equilibrium experiments with the set of reaction of proton abstraction from 4-nitrophenyl[bis(ethylsulphonyl)]methane in acetonitrile are reported. Two strong organic bases are used: 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). The rates of proton transfer reaction have been measured by T-jump method in the presence of perchlorate of the appropriate base as a common cation BH⁺ and supporting electrolyte-tetrabutylammonium perchlorate (TBAP) in the temperature range between 20–40°C are: k _H =1.32×10⁷−2.00×10⁷ and 2.82×10⁷−4.84×10⁷ dm ³mol⁻¹s⁻¹ for MTBD and TBD respectively. The enthalpies of activation ΔH _MTBD ^≠ =13.5 and ΔH _TBD ^≠ =18.1 kJmol⁻¹. The entropies of activation are negative: ΔS _MTBD ^≠ =−62.3 and ΔS _TBD ^≠ =−40.3 Jmol⁻¹K⁻¹. The change of the absorbance of the anion of 4-nitrophenyl[bis9ethylsulphonyl)]methane at the temperature 25°C in the presence of common cation BH⁺ gives the equilibrium constants K=705 and 906 M⁻¹ for MTBD and TBD respectively. Kinetic and equilibrium results are discussed. The possible mechanism of proton transfer reaction between 4-nitrophenyl[bis(ethylsulphonyl)]methane and cyclic organic bases: MTBD and TBD in acetonitrile is proposed.     

Effect of protonation and deprotonation on surface charge density of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>

The protonation and deprotonation of the Nb₂O₅ surface has been followed in order to understand the reactions of surface of this catalyst. The simultaneous potentiometric and conductometric titrations had been carried by using 50 mL of water suspension of Nb₂O₅ 40 g L⁻¹. The oxide was entirely deprotonated when adding 0.4 mL NaOH 1 mol L⁻¹, and later titrated with 0.1 mol L⁻¹. The titration had supplied K ₁ and K ₂ and the obtained values were 3.24 × 10⁻³ and 4.17 × 10⁻⁸, respectively. The zero point charge was pH_pcz = 4.94. The thermodynamic studies were carried out by using 50 mL of a 40 g/L Nb₂O₅ aqueous suspension with the pH adjusted to pH_PZC value. The suspension was titrated with 0.5 mol/L of HNO₃ or NaOH for protonation or deprotonation studies, respectively, in an isoperibol calorimeter CSC ISC-4300. Thus, the obtained thermodynamic values of the protonation and deprotonation of Nb₂O₅ were Δ_dp G = −37.60 kJ/mol, Δ_dp H = −23.72 kJ/mol and Δ_dpS = 47 J/(mol K).     

Ion-exchange selectivity of a network calixarene-containing polymer obtained by the template synthesis on Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, and Ba<Superscript>2+</Superscript> matrices

The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na⁺, K⁺, and Ba²⁺ as matrices was studied. The selectivity coefficients of ion exchanges Ba²⁺-H⁺, Na⁺-H⁺, K⁺-H⁺, Na⁺-K⁺, and Na⁺-NH₄ ⁺ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol⁻¹. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005.     

DFT studies on the structures and stabilities of N<Subscript>5</Subscript><Superscript>+</Superscript>-containing salts

Density functional theory (DFT) methods have been applied to study the properties of series of N₅ ⁺ salts. The thermal stabilities of the crystals are evaluated based on the reaction enthalpy (ΔH) and free energy change (∆G) of the salts when they dissociate into neutral products. The energy outputs of salts in explosion indicate that all N₅ ⁺ salts yield large energy except for N₅SbF₆ and N₅Sb₂F₁₁. Considering the released energy and thermal stability, (N₅)₂SnF₆, N₅PF₆, N₅BF₄, and N₅SO₃F may be potential candidates of very energetic explosives.     

Inertness of C<Subscript>60</Subscript> fullerene toward RO<Subscript>2</Subscript><Superscript>·</Superscript> peroxy radicals

The reactivity of fullerene C₆₀ toward peroxy radicals RO₂ ^· was tested by the chemiluminescence method. A comparison of the influence of C₆₀ and known inhibitors on the kinetics of liquid-phase chemiluminescence (CL) during oxidation of a series of hydrocarbons (ethyl-benzene, cyclohexane, n-dodecane, and oleic acid) shows that the fullerene does not react with the RO₂ ^· radicals. A sharp decrease in the CL intensity observed upon C₆₀ addition is caused by the quenching of CL emitters with fullerene but not by inhibition of hydrocarbon oxidation. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1808–1811, August, 2005.     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

Robust Inclusion Complexes of Crown Ether Fused Tetrathiafulvalenes with Li+@C60 to Afford Efficient Photodriven Charge Separation

Inclusion complexes of benzo‐ and dithiabenzo‐crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li⁺@C₆₀ ( 1? Li⁺@C₆₀ and 2? Li⁺@C₆₀). The strong complexation has been quantified by high binding constants that exceed 10⁶ M ^?1 obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6‐311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li⁺ have a crucial role in robust complex formation. Interestingly, complexation of Li⁺@C₆₀ with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding ³(Li⁺@C₆₀)*, when no charge separation by means of ¹Li⁺@C₆₀* occurs. Photoinduced charge separation by means of ³Li⁺@C₆₀* with lifetimes of 135 and 120 μs for 1? Li⁺@C₆₀ and 2? Li⁺@C₆₀, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time‐resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron‐transfer events in the corresponding complex.     

Second Dissociation Constant of H<Subscript>2</Subscript>Te and the Absorption Spectra of HTe<Superscript>–</Superscript>, Te<Superscript>2–</Superscript> and Te<Subscript>2</Subscript><Superscript>2–</Superscript> in Aqueous Solution

We have measured the second acid dissociation constant, K _2a , at several ionic strengths for hydrogen telluride (H₂Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe⁻ and Te²⁻. Since it is produced in our solutions, we have also determined the spectra of Te₂ ²⁻ both in the uv and in the visible regions. At 25 ^∘C, K _2a = (1.28 ± 0.02) × 10⁻¹² by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm^-3 was estimated to be (8.7 ± 0.2) × 10⁻¹². The solution thermodynamics of these species are also discussed and comparisons are made to related acids.     

Thermodynamic properties of strontium metaniobate SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

The heat capacity and the enthalpy increments of strontium metaniobate SrNb₂O₆ were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C _pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·10⁶/T ² J K⁻¹ mol⁻¹ (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S _m⁰ (298.15 K)=173.88±0.39 J K⁻¹ mol⁻¹ was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δ_f H ⁰ (298.15 K)=-2826.78 kJ mol⁻¹ was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.