From unsaturated dodecahedranes to C40 cages?

(2+2)-Dimerization of unsaturated, highly pyramidalized dodecahedranes (Φ = 43-45°) is explored as a route to C₄₀-cage molecules and non-classical ions derived thereby. The cycloadducts (X-ray structure) formed under vigorous conditions either in solution or in the solid phase above 300 °C did not undergo 2σ → 2π isomerization. The MS fragmentation patterns, in line with calculations (B3LYP/6-31G*), suggest the formation of ‘open’ C₄₀ dications.     

Hydrogen-bonded systems between monocarboxylic acids and the trinuclear cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]: cold-spray ionisation mass spectroscopic and X-ray crystallographic studies

The hydrogen-bonded systems formed between monocarboxylic acid derivatives and the trinuclear arene-ruthenium cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺ (1) have been studied in solution by cold-spray ionisation mass spectroscopy (CSI-MS) and in the solid state by single-crystal X-ray structure analysis of the tetrafluoroborate salts. The presence of 1:1 (acid:cluster) adducts in acetone solution has been clearly demonstrated by CSI-MS. Single-crystal X-ray structure analyses of selected acid-cluster complexes show that in every case the hydroxyl of the acid function interacts strongly with the μ₃-oxo ligand of cation 1, the O ? O distance ranging from 2.499(9) to 2.595(11) Å.     

Reaction of C60 with KMnF4 : Isolation and characterization of a new isomer of C60F8 and re-evaluation of the structures of C60F7(CF3) and the known isomer of C60F8

The volatile fluorofullerene products of high-temperature reactions of C₆₀ with the ternary manganese(III, IV) fluorides KMnF₄, KMnF₅, A₂MnF₆ (A⁺ = Li⁺, K⁺, Cs⁺), and K₃MnF₆ were monitored as a function of reaction temperature, reaction time, and stoichiometric ratio by in situ Knudsen-cell mass spectrometry. When combined with fluorofullerene product ratios from larger-scale (bulk) screening reactions with the same reagents, an optimized set of conditions was found that yielded the greatest amount of C₆₀F₈ (KMnF₄/C₆₀ mol ratio 28-30, 470 °C, 4-5 h). Two isomers of C₆₀F₈ were purified by HPLC, one of which has not been previously reported. Quantum chemical calculations at the DFT level combined with 1D and 2D ¹⁹F NMR, FTIR, and FT-Raman spectroscopy indicate that the C₆₀F₈ isomer previously reported to be 1,2,3,8,9,12,15,16-C₆₀F₈ is actually 1,2,3,6,9,12,15,18-C₆₀F₈, making it the first high-temperature fluorofullerene with non-contiguous fluorine atoms. The new isomer, which was found to be 1,2,7,8,9,12,13,14-C₆₀F₈, is predicted to be 5.5 kJ mol⁻¹ more stable than 1,2,3,6,9,12,15,18-C₆₀F₈ at the DFT level. In addition, new DFT calculations and spectroscopic data indicate that the compound previously isolated from the high-temperature reaction of C₆₀ and K₂PtF₆ and reported to be 16-CF₃-1,2,3,8,9,12,15-C₆₀F₇ is actually 18-CF₃-1,2,3,6,8,12,15-C₆₀F₇.     

A widely varying range of products in reactions of C6F5BrF2, C6F5IF2, and C6F5IF4 with Lewis acids of different strength

The relative fluoride donor ability: C₆F₅BrF₂ > C₆F₅IF₂ > C₆F₅IF₄ was outlined from reactions with Lewis acids of graduated strength in different solvents. Fluoride abstraction from C₆F₅HalF₂ with BF₃·NCCH₃ in acetonitrile (donor solvent) led to [C₆F₅HalF·(NCCH₃)_n][BF₄]. The attempted generation of [C₆F₅BrF]⁺ from C₆F₅BrF₂ and anhydrous HF or BF₃ in weakly coordinating SO₂ClF gave C₆F₅Br besides bromoperfluorocycloalkenes C₆BrF₇ and 1-BrC₆F₉. In reactions of C₆F₅IF₂ with SbF₅ in SO₂ClF the primary observed intermediate (¹⁹F NMR, below 0 °C) was the 4-iodo-1,1,2,3,5,6-hexafluorobenzenium cation, which converted into C₆F₅I and 1-IC₆F₉ at 20 °C. The reaction of C₆F₅IF₄ with SbF₅ in SO₂ClF below −20 °C gave the cation [C₆F₅IF₃]⁺ which decomposed at 20 °C to C₆F₅I, 1-iodoperfluorocyclohexene, and iodoperfluorocyclohexane. Principally, the related perfluoroalkyl compound C₆F₁₃IF₄ showed a different type of products in the fast reaction with AsF₅ in CCl₃F (−60 °C) which resulted in C₆F₁₄. Intermediate and final products of C₆F₅HalF_n−1 (n = 3, 5) with Lewis acids were characterized by NMR in solution. Stable solid products were isolated and analytically characterized.     

Reinvestigation and superstructure of La3.67[Fe(C2)3]

The lanthanum iron carbide La_3.67[Fe(C₂)₃] was prepared from the elements by argon arc-melting followed by annealing. The crystal structure of the ternary phase was reported previously (space group P6₃/m with a=878.7(2) pm, and c=535.1(1) pm) [A.M. Witte, W. Jeitschko, Z. Naturforsch. 51b (1996) 249-255]. In the present work the compound was reinvestigated by X-ray powder and single crystal diffraction, and was further characterized by metallographic methods and chemical analyses. Our diffraction data clearly reveal a superstructure with weak superstructure reflections in the space group P6₃/m with a=879.26(8) pm and c=1604.59(15) pm, thus tripling the previously reported subcell. The crystal structure (refinement to R1=0.044 and wR2=0.075 for 1387 unique reflections and 60 variables) contains Fe(C₂)₃ trigonal planar groups with the C₂ ligands bonded end-on to the Fe atoms. The C-C distance is typical for a double bond. La atoms as the least electronegative component surround the complex anions and form a framework of face-sharing tricapped trigonal prisms. The resulting hexagonal channels at 0, 0, z of the partial structure with chemical composition La₃FeC₆ are occupied by four additional La atoms per unit cell. These La atoms are fully ordered within a linear chain and display a Peierls-like distortion pattern. However, no long-range order in the a−b plane has been observed due to the random orientation of the chains. Because of the two different orientations which are possible for each chain the situation is similar to an Ising model on a triangular lattice.     

Platinum-alkyl-B(C6F5)3 (or BF3) ‘in situ’ systems as tin(II) halide-free enantioselective hydroformylation catalysts

The dialkyl/diaryl-platinum complexes (Pt(CH₃)₂(bdpp); PtPh₂(bdpp) and Pt(2-Thioph)₂(bdpp), where bdpp stands for (2S,4S)-2,4-bis(diphenylphosphino)pentane) were reacted either with B(C₆F₅)₃, BPh₃ or BF₃. In the presence of PPh₃ or carbon monoxide cationic species with a general formulae [PtR(L)(bdpp)]⁺ (L = PPh₃, CO) were formed exclusively. The ability of boron additives to provide vacant coordination site at the platinum made these systems suitable as hydroformylation catalysts. Enantioselective hydroformylation of styrene was carried out in the presence of in situ catalysts formed from Pt(alkyl/aryl)₂(bdpp) and B(C₆F₅)₃ or BF₃. Moderate e.e-s depending strongly on the structure of the catalytic precursor have been obtained. DFT/PCM calculations reveal an S_N2-type reaction mechanism for the alkyl/aryl ligand abstraction with a notably lower activation barrier for BF₃.     

Selective formation of C60F18(g) and C60F36(g) by reaction of [60]fullerene with molecular fluorine

Fluorination of C₆₀(s), C₆₀(s)-MnF₂(s), C₆₀(s)-NiF₂(s) and C₆₀(s)-MnF₃(s) mixtures has been studied by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination is selective when fullerene reacts with the fluorine chemisorbed on the MnF₂ surface. When the MnF₂ content in the initial mixture is at least 90 mol% both C₆₀F₁₈ and C₆₀F₃₆ are selectively formed. Under certain conditions, mixtures predominantly containing one of three compounds C₆₀F₃₈, C₆₀F₄₀, and C₆₀F₄₂ can be obtained. A consecutive change of the main fluorination products (C₆₀F₁₈ and C₆₀F₃₆) takes place at constant temperature (720 K) and on fluorine admission. A quantitative explanation of this fact is given. Selective fluorination of C₆₀(s) by molecular fluorine is compared with solid-phase fluorination using MnF₃(s) as a fluorinating agent.     

Standard molar enthalpies of formation of Ln(C9H6NO)2(C2H3O2) (Ln: Nd, Sm)

Using an on-line solution-reaction isoperibol calorimeter, the standard molar enthalpies of reaction for the general thermochemical reaction: LnCl₃·6H₂O(s) + 2C₉H₇NO(s) + CH₃COONa(s) = Ln(C₉H₆NO)₂(C₂H₃O₂)(s) + NaCl(s) + 2HCl(g) + 6H₂O(l) (Ln: Nd, Sm), were determined at T=298.15 K, as  kJ mol^−l, respectively. From the mentioned standard molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of Ln(C₉H₆NO)₂(C₂H₃O₂)(s) (Ln: Nd, Sm), at T=298.15 K, have been derived to be: −(1494.7±3.3) and −(1501.5±3.4) kJ mol^−l, respectively.     

Synthesis and molecular structures of heptafluoropropylated fullerenes: C70(n-C3F7)8, C70(n-C3F7)6O, and C70(C3F7)4

Ampoule reactions of C₇₀ with n- and i-C₃F₇I were carried out at 250-310 °C. Two step HPLC separations allowed the isolation of several C₇₀(n-C₃F₇)_4-8 and C₇₀(i-C₃F₇)₄ compounds. Crystal and molecular structures of C₇₀(n-C₃F₇)₈-V, C₇₀(n-C₃F₇)₆O, C₇₀(n-C₃F₇)₄, and three isomers of C₇₀(i-C₃F₇)₄ have been determined by X-ray crystallography using synchrotron radiation. Molecular structures of the new compounds were compared with the known examples and discussed in terms of addition patterns and relative energies of their formation.     

C3 epimerization and selective C2C3 bond fission of alkyl chrysanthemate

Treatment of alkyl chrysanthemate with Lewis acid leads to C₃ epimerization, while protonic acid treatment gives rise to selective C₂C₃ bond cleavage. The latter method is successfully applied to the synthesis of optically active tetrahydrolavandulol.     

The support and characterization of C60 and MoO3 on Al2O3

A new type of catalyst from supporting C₆₀ on MoO₃ and Al₂O₃ has been prepared. The effect of different order of impregnation and calcination atmosphere on catalyst are investigated by the solution test in toluene, UV-VIS spectroscopy and temperature programmed reduction (TPR). The results show that when the catalyst was prepared by supporting MoO₃ on C₆₀/Al₂O₃ and calcined in N₂, there is a stronger interaction between C₆₀, MoO₃ and Al₂O₃, but when supporting C₆₀ on MoO₃/Al₂O₃, the interaction is relatively weak. We consider that in the former method a new complex, Mo–C₆₀–O–Al, is formed.     

Energy analysis of metal-metal bonding in [RM-MR] (M = Zn, Cd, Hg; R = CH3, SiH3, GeH3, C5H5, C5Me5)

The metal-metal bonds of the title compounds have been investigated with the help of energy decomposition analysis at the DFT/TZ2P level. In good agreement with experiment, computations yield Hg-Hg bond distance in [H₃SiHg-HgSiH₃] of 2.706 Å and Zn-Zn bond distance in [(η⁵-C₅Me₅)Zn-Zn(η⁵-C₅Me₅)] of 2.281 Å. The Cd-Cd bond distances are longer than the Hg-Hg bond distances. Bond dissociation energies (-BDE) for Zn-Zn bonds in zincocene −70.6 kcal/mol in [(η⁵-C₅H₅)₂Zn₂] and −70.3 kcal/mol in [(η⁵-C₅Me₅)₂Zn₂] are greater amongst the compounds under study. In addition, [(η⁵-C₅H₅)₂M₂] is found to have a binding energy slightly larger than those in [(η⁵-C₅Me₅)₂M₂]. The trend of the M-M bond dissociation energy for the substituents R shows for metals the order GeH₃ < SiH₃ < CH₃ < C₅Me₅ < C₅H₅. Electrostatic forces between the metals are always attractive and they are strong (−75.8 to −110.5 kcal/mol). The results demonstrate clearly that the atomic partial charges cannot be taken as a measure of the electrostatic interactions between the atoms. The orbital interaction (covalent bonding) ΔE_orb is always smaller than the electrostatic attraction ΔE_elstat. The M-M bonding in [RM-M-R] (R = CH₃, SiH₃, GeH₃, C₅H₅, C₅Me₅; M = Zn, Cd, Hg) has more than half ionic character (56-64%). The values of Pauli repulsions, ΔE_Pauli, electrostatic interactions, ΔE_elstat, and orbital interactions, ΔE_elstat are larger for mercury compounds as compared to zinc and cadmium.     

Preparation and crystal structure of [Bi3I(C4H8O3H2)2(C4H8O3H)5]2Bi8I30 containing the novel polynuclear [Bi8I30] anion

Preparation and crystal structure of the novel compound [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ are reported. The title compound is prepared by heating of BiI₃ and diethylene glycol at 413 K in a sealed quartz glass tube filled with argon. Deep red single crystals are grown and applied to perform X-ray powder diffraction and X-ray single-crystal diffraction measurements. The compound crystallizes triclinic with space group P-1: Z=2, a=13.217(1) Å, b=15.277(1) Å, c=22.498(1) Å, α=84.33(1), β=73.18(1), γ=67.48(1). [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ comprises the novel polynuclear [Bi₈I₃₀]⁶⁻ anion and [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]³⁺ as the cation. Cation as well as the anion can be assumed to represent intermediates between solid BiI₃ and BiI₃ completely dissolved in diethylene glycol.     

C60F14OFPh3, a fluoroxy derivative of C60F15Ph3; evidence for the presence of ‘missing’ fluorine through restricted rotation of a phenyl group

From the reaction of C₆₀F₁₈ with benzene in the presence of SbCl₅ we have isolated a compound of 1252 amu indicated to be C₆₀F₁₄OFPh₃, a fluoroxyfullerene. Temperature-variable ¹H NMR shows that one phenyl group suffers restricted rotation on cooling to 218 K, attributed to the presence of the OF group which, as in the case of the recently characterised C₆₀F₁₇OF, fails to give a signal for this group in the ¹⁹F NMR. We have isolated also, C₆₀F₁₄O₂FPh₃ (1268 amu) a mixture of oxahomo derivatives of C₆₀F₁₄OFPh₃ arising from oxygen insertion into FCCF bonds. Theoretical calculations for C₆₀F₁₄OFPh₃ indicate that the phenyl group nearest to the OF group is twisted out of the plane containing the other two.     

Thermodynamic properties of BaCeO3 and BaZrO3 at low temperatures

Specific heat capacities (C_p) of polycrystalline samples of BaCeO₃ and BaZrO₃ have been measured from about 1.6 K up to room temperature by means of adiabatic calorimetry. We provide corrected experimental data for the heat capacity of BaCeO₃ in the range T < 10 K and, for the first time, contribute experimental data below 53 K for BaZrO₃. Applying Debye's T³-law for T → 0 K, thermodynamic functions as molar entropy and enthalpy are derived by integration. We obtain C_p = 114.8 (±1.0) J mol⁻¹ K⁻¹, S° = 145.8 (±0.7) J mol⁻¹ K⁻¹ for BaCeO₃ and C_p = 107.0 (±1.0) J mol⁻¹ K⁻¹, S° = 125.5 (±0.6) J mol⁻¹ K⁻¹ for BaZrO₃ at 298.15 K. These results are in overall agreement with previously reported studies but slightly deviating, in both cases. Evaluations of C_p(T) yield Debye temperatures and identify deviations from the simple Debye-theory due to extra vibrational modes as well as anharmonicity. The anharmonicity turns out to be more pronounced at elevated temperatures for BaCeO₃. The characteristic Debye temperatures determined at T = 0 K are Θ₀ = 365 (±6) K for BaCeO₃ and Θ₀ = 402 (±9) K for BaZrO₃.     

Synthesis and crystal structure of Ir(C2H4)2(C5H7O2)

We report a new synthesis and characterization of Ir(C₂H₄)₂(C₅H₇O₂) [(acetylacetonato)-bis(η²-ethene)iridium(I)], prepared from (NH₄)₃IrCl₆ · H₂O in a yield of about 45%. The compound has been characterized by X-ray diffraction crystallography, infrared, Raman, and NMR spectroscopies and calculations at the level of density functional theory. Ir(C₂H₄)₂(C₅H₇O₂) is isostructural with Rh(C₂H₄)₂(C₅H₇O₂), but there is a substantial difference in the ethylene binding energies, with Ir-ethylene having a stronger interaction than Rh-ethylene; two ethylenes are bound to Ir with a binding energy of 94 kcal/mol and to Rh with a binding energy of 70 kcal/mol.     

Synthesis and molecular structures of heptafluoroisopropylated fullerenes: C60(i-C3F7)8, C60(i-C3F7)6, and C60(CF3)2(i-C3F7)2

One isomer of C₆₀(i-C₃F₇)₈, three isomers of C₆₀(i-C₃F₇)₆, and the first mixed perfluoroalkylated fullerene, C₆₀(CF₃)₂(i-C₃F₇)₂, have been isolated by HPLC from a mixture prepared by reaction of C₆₀ with heptafluoroisopropyl iodide in a glass ampoule at 260-290 °C. The molecular structures of the four new compounds have been determined by means of X-ray single crystal diffraction partially also by use of synchrotron radiation. Theoretical calculations at the DFT level of theory have been employed to rationalize the energetics of isomers and of C₆₀-R_f binding.     

Synthesis and crystal structure of [C6H5Hg(H2NSiMe3)][H2N{B(C6F5)3}2], a phenyl-mercury(II) cation stabilised by a non-coordinating counter-anion

The new heteroleptic mercury(II) complex PhHgN(SiMe₃)₂(1) reacts with the strong Brønsted acid [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] with cleavage of a N-Si bond to give [C₆H₅Hg(H₂NSiMe₃)][H₂N{B(C₆F₅)₃}₂] (2), a phenyl-mercury(II) cation stabilised by a primary amine and a non-coordinating counter-anion. Attempts to generate donor-free aryl mercury cations were not successful. The crystal structure of 2 · CH₂Cl₂ shows short π-bonding interactions between the metal and the phenyl ring of a neighbouring cation; the geometry about the mercury(II) atom is nearly linear. The X-ray structures of the new salts [H₂N(SiMe₃)₂ · H₃NSiMe₃][B(C₆F₅)₄]₂ and [Et₃O][H₂N{B(C₆F₅)₃}₂] · CH₂Cl₂ are also presented.     

The new silver(I)thioantimonate(III) [C4N2H14][Ag3Sb3S7] and a new structural variant of the silver(I)thioantimonate(III) [C2N2H9]2[Ag5Sb3S8] both synthesized under solvothermal conditions

The novel silver(I)thioantimonates(III) [C₄N₂H₁₄][Ag₃Sb₃S₇] (I) (C₄N₂H₁₂=1,4-diaminobutane) and [C₂N₂H₉]₂[Ag₅Sb₃S₈] (II) (C₂N₂H₈=ethylenediamine) were synthesized under solvothermal conditions using AgNO₃, Sb, S and the amines as structure directing molecules. Both compounds crystallize as orange needles with lattice parameters a=6.669(1) Å, b=30.440(3) Å, c=9.154(1) Å for I (space group Pnma), and a=6.2712(4) Å, b=15.901(1) Å, c=23.012(2) Å, β=95.37(1)° for II (space group P2₁/n). In both compounds the primary building units are trigonal SbS₃ pyramids, AgS₃ triangles and AgS₄ tetrahedra. In I the layered [Ag₃Sb₃S₇]²⁻ anion is constructed by two different chains. An [Sb₂S₄] chain running along [100] is formed by vertex sharing of SbS₃ pyramids. The second chain contains a Ag₃SbS₅ group composed of the AgS₄ tetrahedron, two AgS₃ units and one SbS₃ pyramid. The Ag₃SbS₅ units are joined via S atoms to form the second chain which is also directed along [100]. The layered anion is then obtained by condensation of the two individual chains. The organic structure director is sandwiched by the inorganic layers and the shortest inter-layer distance is about 6.4 Å. In II the primary building units are linked into different six-membered rings which form a honeycomb-like layer. Two such layers are connected via Ag-S bonds of the AgS₄ tetrahedra giving the final undulated double layer anion. The structure directing ethylenediamine cations are located in pairs between the layers and a sandwich-like arrangement of alternating anionic layers and organic cations is observed. The inter-layer separation is about 5.4 Å. Both compounds decompose in a more or less complex manner when heated in an argon atmosphere. The optical band gaps of about 1.9 eV for the two compounds proof the semiconducting behavior. For II the conductivity was measured with impedance spectroscopy and amounts to σ_295K=7.6×10⁻⁷ Ω⁻¹ cm⁻¹. At 80 °C the conductivity is significantly larger by one order of magnitude.     

Higher trifluoromethylated derivatives of C60, C60(CF3)16 and C60(CF3)18: Synthesis, structure, and theoretical study

Three isomers of C₆₀(CF₃)₁₆ and one isomer of C₆₀(CF₃)₁₈ have been isolated by HPLC from a mixture prepared by trifluoromethylation of C₆₀ with CF₃I in a glass ampoule at 380-400 °C. The molecular structures of the four new compounds have been determined by means of X-ray single crystal diffraction and discussed in terms of mechanistic pathways of their formation and relative stability according to the DFT calculations.