Sm@C74: Computed Relative Isomeric Populations

Density-functional theory (DFT) calculations are reported for Sm@C₇₄, namely for Sm encapsulation in the IPR (isolated pentagon rule) C₇₄ cage and in two C₇₄ cages with a pentagon-pentagon junction. Their relative thermodynamic production yields are evaluated using the DFT calculated terms and it is shown that the IPR-based Sm@C₇₄ endohedral prevails at relevant temperatures in agreement with observation, however, isolation of a minor isomer could be possible.     

Eu@C86 isomers: Calculated relative populations

Abstract

Relative populations of four energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C₈₆ are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/3-21G?～?SDD entropy term, M06-2X/6-31G*～SDD or B2PLYP(D)/6-31G*～SDD energetics). The calculations confirm that the recently isolated Eu@C₁(7)-C₈₆ species is a major isomer in a relevant temperature region. Relationship to the empty C₈₆ cages is discussed, too.     

A Bent Tb2C2 Cluster Encaged in a CS (6)-C82 Cage: Synthesis,Isolation and X-ray Crystallographic Study

Terbium (Tb)-based dimetallofullerene, Tb₂C₈₄, has been synthesized and isolated by multistep HPLC. According to the UV-vis-NIR spectroscopic characterization and comparison with the reported analogous M₂C₈₄ (M = Sc, Y) metallofullerenes, the molecular structure of Tb₂C₈₄ is proposed to be Tb₂C₂@C_s (6)-C₈₂ featuring a metal carbide clusterfullerene (CCF) structure, which is unambiguously confirmed by X-ray crystallographic study. A detailed analysis of the crystal structure of a cocrystal of Tb₂C₂@C_s (6)-C₈₂·Ni^II(OEP)·2C₆H₆ (Ni^II(OEP) = nickel (II) octaethylporphyrin) reveals that a bent Tb₂C₂ carbide cluster is encaged rigidly inside a C_s (6)-C₈₂ cage. The C-C bond within the encaged Tb₂C₂ carbide cluster behaves as a typical C-C triple bond. The asymmetric unit in Tb₂C₂@C_s (6)-C₈₂·Ni^II(OEP)·2C₆H₆ contains two fullerene sites, for which the encaged Tb₂C₂ carbide cluster however locates at nearly the same position with one Tb atom being beneath a hexagon and another Tb atom pointing to the conjunction of two adjacent hexagons.     

Triplet molecules of the D5 symmetry group based on C60 fullerene

The possibility of observing a non-zero-spin triplet state in highly symmetric derivatives of fullerene molecules with five double bonds, representing isomers of the type D₅-C₆₀(R-r ₆-R)₅ (where R = H or CH₃), is assessed based on the results of quantum-chemical calculations. The energies of isomer formation (endo-and exothermal process for the hydrogenated and methylated isomers, respectively) and the energies of terms are determined. The ground state corresponding to a non-zero-spin triplet e ₁ ² (³A₂) occurs approximately 0.3 eV below the zero-spin states. The results can be interpreted within the framework of the tight binding approximation for the pπ basis set orbitals of fullerene molecules (representing radially directed C2p hybrid atomic orbitals). The character of the open electron shell of isomers, delocalized over a large fullerene surface, suggests that, with high probability, the above non-zero-spin triplet state (rather than the e ₁ ² (¹E₂) state stabilized by the Jahn-Teller effect) is the ground state of the system.     

Chemical Properties of Divalent Metallofullerenes Yb@D 3h(1)-C74 and Yb@C 2(13)-C84

Endohedral metallofullerenes (EMFs) encapsulating divalent metal ions have rarely been studied because of their low production yields. We report here for the first time the chemical understanding of two typical divalent EMFs, i.e. Yb@D_3h-C₇₄ and Yb@C₂(13)-C₈₄ with a disilirane reagent (1), which has shown great success in probing the chemical reactivity of EMFs encapsulating a variety of metallic cores. It was surprising to find that Yb@D_3h(1)-C₇₄ reacted with 1 neither thermally nor photochemically under normal conditions, showing an unusually low reactivity. However, monoadduct formation was achieved by laser-irradiation of their mixtures during the mass spectroscopic measurement. Accordingly, the thermal and photochemical reactions of Yb@C₂(13)-C₈₄ with 1 were conducted under harsher conditions and monoadduct formation was confirmed by both chromatographic and mass spectroscopic studies. The relatively low reactivity of these divalent EMFs compared with that of the corresponding trivalent analogues is attributed to their more negative first reduction potentials, as well as their close-shell electronic configurations, presenting new insights into the templating effect of the internal metal ion on the chemical properties of the cage carbons of EMFs.     

Computations on Metallofullerenes Derivatized during Extraction: La@C80-C6H3Cl2 and La@C82-C6H3Cl2

Recently, an extraction of la metallofullerenes from soot using 1,2,4-trichlorobenzene has been reported for La@C₈₀ and La@C₈₂. In both cases, the cages were derivatized by the solvent (forming La@C₈₀-C₆H₃Cl₂ and La@C₈₂-C₆H₃Cl₂) and the following X-ray analysis disclosed rather unexpected cages: C₈₀(C _2v ;3) and C₈₂(C _3v ;7). In order to explain the challenging observations, a two-step computational treatment is presented. The first step deals with the high-temperature gas-phase formation of the underivatized endohedrals while the second step models the reaction with the solvent. The Gibbs free energies were evaluated for representative temperatures and the computational scheme was able to confirm high relative populations for the observed derivatized cages.     

On the Formation and Stability of Fullerenes

Abstract

Fullerenes (especially the higher ones) degrade to an insoluble material on storage in air. The C _2v(II) isomer of [78]fullerene is completely degraded after storage for 5 months. The extreme instability may account for the variable yields of this isomer obtained by different research groups. Strong heating of KBr discs of these insoluble materials produces CO₂ showing that they are oxygen containing. Given this inherent instability of fullerenes, the question arises as to why they are formed in the first place. It is argued that the formation is not a unique consequence of the need to eliminate dangling bonds produced during carbon vaporisation by the arc-discharge procedure. Rather, fullerene formation is favoured by a higher intramolecular dangling-bond collision frequency (i.e. much higher Arrhenius A-factor) for cage closure compared to the intermolecular collisions that lead to the more stable graphitic sheets.     

Ideal gas thermodynamic properties of simple alkanols

The ideal gas thermodynamic properties [C _p ⁰ , S ⁰(T) –S ⁰(0) and H ⁰(T)-H⁰(0)] of methanol (CH₃OH), ethanol (C₂H₅OH), 1-propanol (CH₃CH₂CH₂OH), and 2-propanol [(CH₃)₂CHOH] over the temperature range 0 to 1500 K at 1.01325-bar (1-atm) pressure are calculated by the statistical mechanical method, employing the recent molecular and spectroscopic constants. The internal rotational contributions to the thermodynamic properties caused by the presence of -CH₃, -C₂H₅, and -OH rotors in these molecules are evaluated using an internal rotational partition function formed by the summation of internal rotational energy levels for each rotor. In the calculation of the thermodynamic properties of ethanol (g) and 1-propanol (g), we adopted a molecular model that the vapor of each compound contains an equilibrium mixture of trans and gauche isomers. The existence of such isomers was observed spectroscopically in recent years. Our calculated results, such as C _p ⁰ and S ⁰(T) ****-S ⁰(0), agree with available experimental values.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, USA     

Effect of structural relaxation on critical fieldsH c andH c2 and on resistivity in sputtered amorphous alloys Zr76Cu24 and Zr76Ni24

We report critical field results on sputtered amorphous Zr₇₆Cu₂₄ and Zr₇₆Ni₂₄ alloys. TheH _c (T) obtained from calorimetric measurements is well described by assuming that both systems are weak coupling superconductors. A similar good agreement is not found forH _c2 (T) obtained by a resistive method; tentative explanations of this discrepancy are suggested. We also report resistivity measurements in the normal state on Zr₇₆Ni₂₄ alloys. Results are well interpreted in the framework of the Faber-Ziman diffraction model. An alternative explanation, the Kondo-like model for two-level systems, is also discussed.Also at the Service National des Champs Intenses.     

Structural strain in pyrites evaluated by X-ray powder diffraction

Two parameters for measuring the structural strain, the effective Debye-Waller parameter, B _eff, and lattice strain, , were evaluated on a natural pyrite (FeS₂) after grinding. The effective Debye-Waller parameter, B _eff, which depends on the displacement of atoms in the crystal, was calculated for the overall crystal, B _eff(FeS₂), and for sulphur, B _eff(S), from the intensities of the X-ray diffraction lines. The B _eff(S) increased markedly with increasing grinding time, while B _eff(FeS₂) did not change significantly. The lattice strain, , was not recognized. These observations suggest that the displacement of sulphur atoms preferentially takes place by grinding. The relations between these B _eff values and crystallite size, L, were observed to be common for two different methods of grinding. This tendency was considered to be an inherent property of pyrite. The value of B _eff(S) is a useful index to estimate mechanically caused strain in pyrite.     

Thermodynamic functions for the formation of isomeric CF3 adducts of C70 and C84

Gas-phase formation enthalpies and Gibbs energies of formation (Δ_fH°_m; Δ_fG°_m) of trifluoromethylderivatives of fullerenes C₇₀ and C₈₄ are calculated at the DFT (density functional theory) level of theory. The approach employs homodesmic (HD) transtrifluoromethylation reactions and experimental thermochemical data on C₆₀, C₇₀, C₈₄ and S₆-C₆₀(CF₃)₁₂.     

Maximal Non-Adjacent Addition to Fullerene-70: Computation of All the Closed Shell Isomers of C70X26

Abstract

Computation of the patterns for saturation non-adjacent addition to D_5h-C₇₀ to yield closed-shell products shows that maximal addition is achieved with C₇₀X₂₆. There are ten possible addition patterns and the relative energies of these isomers is assessed by simple Hückel and molecular modelling calculations (for X = H and CH₃). the identity of the lowest energy isomer is found to depend upon the size of the addend.     

A single crystal X-ray diffraction study of Na4(UO2)4(i-C4H9COO)11(NO3)·3H2O

Synthesis and the results of IR and single crystal X-ray diffraction study of Na₄(UO₂)₄(i-C₄H₉COO)₁₁·(NO₃)·3H₂O are reported. The crystals are monoclinic; the unit cell parameters at 100 K are as follows: a = 13.697(2), b = 20.285(3), c = 15.991(3) Å, β = 103.760(3)°, space group P2₁, Z = 2, R = 0.0650. The uraniumcontaining structural units are mononuclear moieties [UO₂(i-C₄H₉COO)₃]^? and [UO₂(NO₃)(i-C₄H₉COO)₂]^?, belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = i-C₄H₉COO^? and NO ₃ ^? ) of uranyl complexes. The IR data are consistent with the results of the single crystal X-ray diffraction study. The influence of the carboxylate ligand volume on the structure of Na[UO₂L₃]·nH₂O crystals (L = acetate, n-butyrate, isovalerate ion) is analyzed.     

Isolation and Crystallographic Characterization of Tm3N@D2 (35)-C88

Tm₃N@D₂(35)-C₈₈ has been prepared by vaporization of graphite rods doped with Tm₂O₃, graphite powder, and iron nitride in a Krätschmer-Huffman arc-discharge fullerene generator and isolated by high pressure liquid chromatography. A single crystal X-ray diffraction study reveals the dimensions of the D₂(35)-C₈₈ cage and the positioning of the Tm₃N unit inside.     

Calculations of the water-dimer encapsulations into C84

The water-dimer formation and its encapsulation into D₂(22)-C₈₄ and D_2d(23)-C₈₄ fullerenes is evaluated. The water-dimer populations are computed using the potential-energy change from the G3 theory and anharmonic partition functions from the MP2/AUG-cc-pVQZ approach. The encapsulation energetics is treated at the M06-2X/6-31++G** level and it is found that the water-dimer storage in C₈₄ is attractive, yielding an energy gain of more than 10 kcal mol^?1. This substantial encapsulation energy together with the computed temperature increase of the water-dimer population in the saturated steam suggests that the (H₂O)₂@C₈₄ endohedrals could be produced in a high-temperature/high-pressure approach similarly to encapsulation of rare gases in fullerenes.     

Phase diagrams of the ternary liquid systems [Ce(NO3)3(TBP)3]-C10H22-[UO2(NO3)2(TBP)2] and [Ce(NO3)3(TBP)3]-C10H22-[Th(NO3)4(TBP)2] and of the quaternary liquid system [Ce(NO3)3(TBP)3]-C10H22-[UO2(NO3)2(TBP)2]-[Th(NO3)4(TBP)2]

The phase diagrams of the ternary liquid systems [Ce(NO₃)₃(TBP)₃]-C₁₀H₂₂-[UO₂(NO₃)₂(TBP)₂] and [Ce(NO₃)₃(TBP)₃]-C₁₀H₂₂-[Th(NO₃)₄(TBP)₂] and of the quaternary liquid system [Ce(NO₃)₃(TBP)₃]-C₁₀H₂₂-[UO₂(NO₃)₂(TBP)₂]-[Th(NO₃)₄(TBP)₂] at T = 298.15 K are constructed. The phase diagrams are characterized by areas of homogeneous solutions and of two-phase liquid systems (systems with phase separation), with one phase (I) enriched in [Ce(NO₃)₃(TBP)₃], [Th(NO₃)₄(TBP)₂], and [UO₂(NO₃)₂(TBP)₂], and the other phase (II), in C₁₀H₂₂. Using the data on the mutual solubility of the components in the systems under consideration and equations of the NRTL model, the parameters of intermolecular interactions and the excess Gibbs energies (G ^ex) were calculated for the binary, ternary, and quaternary systems. Passing from the ternary system [Ce(NO₃)₃(TBP)₃]-C₁₀H₂₂-[Th(NO₃)₄(TBP)₂] to the quaternary system [Ce(NO₃)₃(TBP)₃]-C₁₀H₂₂-[UO₂(NO₃)₂ (TBP)₂]-[Th(NO₃)₄(TBP)₂] does not appreciably affect the distribution of C₁₀H₂₂ between phases I and II, but leads to the redistribution of [Ce(NO₃)₃(TBP)₃] into phase II and of [Th(NO₃)₄(TBP)₂] into phase I.     

Orientational ordering in solid D2 from NMR studies. I. The hcp phase

Using a coherent pulsed NMR spectrometer operating at 5.9 MHz, measurements have been made of the free induction decay and of the solid echo in hcp solid D₂. From these data, and using Fourier transform techniques, the NMR line shapes and longitudinal relaxation times have been found for both o-D₂ (angular momentumJ=0 and spinI=2) and p-D₂ (withJ=1 andI=1) separately. The concentration and temperature extended over the ranges 0.05X(J=1)0.56 and 0.04<T<3 K, respectively. For both o-D₂ and p-D₂, the second moment of the NMR line shape rises smoothly as the temperature decreases, while the relaxation times pass through a minimum. No evidence of a thermal hysteresis could be found in the line shape or relaxation times. The orientational ordering increases continuously as the temperature decreases and the results lead to the conclusion that there is no evidence for a well-defined transition into a phase that has the characteristics of a glassy state, at least above 0.05 K. Calculations of the rms order parameter for p-D₂ as a function ofX andT are presented and the results compared with those for solid H₂. Above 0.5 K, the agreement is very good, while below 0.3 K, (H₂)>(D₂). The orientational polarization of theJ=0 molecules in D₂ by the surroundingJ=1 molecules is measured from the ratio of the lineshape second moments and is found to be in order-of-magnitude agreement with the predictions by A. B. Harris in the high-temperature limit. An analysis and correlation of the various measured relaxation times via energy diffusion models is presented. From the spin-lattice relaxation times of theJ=1 molecules, the orientational fluctuation rates are estimated for various concentrations as a function ofT and compared with the results from H₂. Good agreement is found. Some unusual features in the intensity ratio of theI=1 andI=2 signals that is different from the expected one are described. In an Appendix, corrections made to the observed line shapes to compensate for the instrumental limitations of the pulse spectrometer are outlined.     

Synthesis and Superconductivity of New Cuprates (Pb0.8W0.2)Sr2(Nd1 ? xCax)Cu2O7 ? δ

New cuprates with nominal composition (Pb_0.8W_0.2)Sr₂(Nd_{1 – x} Ca _x )Cu₂O_{7 –} (0x1) were synthesized by solid-state reaction in N₂. The crystal structure was characterized by X-ray powder diffraction (XRD) as tetragonal. Direct current electrical resistance measurements were applied to check the existence of superconductivity in these cuprates. Superconductivity with T _c (onset) up to 82 K is observed when x = 0.6. Synthesis in N₂ is necessary in obtaining superconductivity in these cuprates. Preparation in air or post-treatment in flowing oxygen destroys superconductivity. A comparison is made with previous Pb-based 1212 superconducting oxides. The valence of Pb and the possible position of W in the lattice are discussed.     

Hot hardness of (Fe,Cr)3C and (Fe,Cr)7C3 carbides

Hot hardness was measured on the primary carbides, (Fe, Cr)₃C and (Fe, Cr)₇C₃, in unidirectionally solidified iron-carbon-chromium hypereutectic alloys with chromium more than 4.8 wt %. The hardness-temperature relation was represented by two Ito-Shishokin formulae,H _v =A(— BT), and thus was drawn by two lines on a semilogarithmic graph. The inflection temperature where the two lines intersected was found at 730 to 860 K for (Fe, Cr)₃C carbide containing 0 to 14 wt % Cr, increasing with an increase in the chromium concentration in the carbide, and at about 910 K for (Fe, Cr)₇C₃ carbide containing 36 to 76 wt % Cr. With increasing chromium concentration in each carbide, the hardness of the carbide increased and the thermal softening coefficients decreased. The effect of chromium on the hardness, the inflection temperature and the thermal softening coefficients was more pronounced for (Fe, Cr)₃C carbide than for (Fe, Cr)₇C₃ carbide. Each of the thermal softening coefficients,B ₁(T<T _t),B ₂(T>T _t), the inflection temperature,T _t, room-temperature hardness,H _v(T _RT), and the hardness atT _t,H _v(T _t), related linearly to the chromium concentration in the carbides, and hence the hot hardness of the carbides could be expressed as functions of temperature and chromium concentration in the carbides. The relationships betweenH _v(T _RT) andH _v(T _t) and between the thermal softening coefficient,B ₂, and the activation energy for creep,Q _c(kJ mol^–1), were represented by the following equations:H _v(T _t)0.7H _v(T _RT),B ₂=1.26/Q _c.