Theoretical studies on the BN substituted fullerenes C70−2x(BN)x (x=1–3)—isoelectronic equivalents of C70

The equilibrium structures and relative stabilities of BN-doped fullerenes C_70−2x(BN)_x (x=1–3) have been studied at the AM1 and MNDO level. The most stable isomers of C_70−2x(BN)_x have been found out and their electronic properties have been predicted. The calculation results show that the BN substituted fullerenes C_70−2x(BN)_x have considerable stabilities, though they are less stable than their all carbon analog. For C₆₈BN, the isomers whose BN is located in the most chemically active bonds of C₇₀ (namely B and A) are among the most stable species, of which B is predicted to be the ground state. The stabilities of C₆₈BN decrease and the dipole moments increase with increasing the distance between the heteroatoms. For C₆₆(BN)₂, the lowest energy species is the isomer in which the B–N–B–N bond is formed; For C₆₄(BN)₃, the most stable species should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The ionization potentials and the affinity energies of the most stable species of BN-doped C₇₀ are almost the same as those of C₇₀ because of the isoelectronic relationship. The ionization potentials and affinity energies depend on the relative position of the heteroatoms in C₆₈BN, the chemical reactivities of the isomers whose heteroatoms are well separated should differ significantly from their all carbon analog.     

Hartree-fock and Hückel-like orbital energies: an elementary extension to Koopmans‘ theorem

For a closed-shell MO configuration with 2n electrons which occupy n non-degenerate canonical MOs, it is deduced that the RHF energy, Σⁿ_i=1[2H⁰_n+Σⁿ_j-1(2J_ij-K_ij)], may be expressed in Hückel-like form as 2Σⁿ_i-1ε, −Σⁿ_i-1[j_i(λ+1)+1,(λ+2)] with λ=2(n-i). The l_i(λ+1) and I_i(λ+2) are the ionization potentials for the HOMO ψ, which arises after λ and λ+1 electrons have been successively removed from the initial configuration.     

Structural characterization of cyclopentadienyl(duroquinone)cobalt dihydrate

The structure of cyclopentadienyl(duroquinone)cobalt dihydrate, (C₅H₅)Co-[(CH₃)₄C₆O₂]·2H₂O, has been determined by three-dimensional X-ray analysis. The crystal structure consists of discrete cyclopentadienyl(duroquinone)cobalt molecules linked together by a complex network of hydrogen bonds between water molecules and duroquinone oxygen atoms. Each (C₅H₅)Co[(CH₃)₄C₆O₂] molecule consists of a cobalt atom sandwiched between a cyclopentadienyl ring and a duroquinone ring. A detailed comparison of the molecular parameters of this complex with those of closely related complexes is given. Crystallographic evidence that the metal---duroquinone interaction in cyclopentadienyl(duroquinone)cobalt dihydrate is considerably stronger than that in the electronically-equivalent 1,5-cyclooctadiene(duroquinone)nickel complex is given not only by the metal---C(olefin) distances being 0.12 Å (av) shorter in the duroquinone---cobalt complex [viz., 2.104(8) Å vs. 2.222(7) Å] but also by the much greater C_2v-type distortion of the duroquinone ring from the planar D_2h configuration in free duroquinone. The compound crystallizes with two formula species in a triclinic unit cell of symmetry P and reduced cell dimensions á = 8.60 Å, b = 9.00 Å, c = 10.15 Å, = 87° 34′, β = 84° 10′, γ = 73° 44′. Least-squares refinement yielded final unweighted and weighted discrepancy factors of R₁ = 10.8% and R₂ = 12.0%, respectively, for 2481 independent diffraction maxima collected photographically.     

Correct calculation of ΔH°, ΔC°P, and ΔV° from temperature and pressure dependences of equilibrium constants: The importance of thermal expansion and compressibility of the solvent

Activities of solutes and compositions of solutions may be expressed corretly in terms of molarity (c), molality (m) or mole fraction (x), leading to corresponding equilibrium constants K_c, K_m, or K_x. Equations for differences between ΔG°_c, ΔG°_m, and ΔG°_x values are derived. Common errors in calculations involving (dlnK_c/dT) and (dlnK_c/dP) are identified and remedies for these errors are presented.     

Gas-phase stability of cluster ions SF m + (SF6) n with m = 0–5 and n = 1–3

The gas-phase stabilities of cluster ions SF⁺_m (SF₆)_n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF⁺_m (SF₆)₁ were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF⁺_m (SF₆)_n with m = 0−4. The structures of SF⁺₅, SF⁺ (SF₆)₁, SF⁺₃ (SF₆)₁, and SF⁺₅ (SF₆)₁ were investigated by ab initio molecular orbital calculations. For SF⁺₅, the D_3h geometry is found to be most stable andC_4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures.     

Diaziridines thermal cleavage possibilities: Disrotatory or conrotatory?

Ab initio calculations are carried out at UB3LYP/6-311++G (3df, 2p) levels of theory, on electrocyclic thermal cleavage of four (S) derivatives of diaziridines, 1_X-R, to their corresponding (Z) and (E) azomethine imides (2_X-Z, 2_X-E, 3_X-Z and 3_X-E), where X=–H, –Me, t-Bu and Ph. Cleavage of 1_X-R Series to 2_X-Z (Path 1) emerged as the more favored, for producing the most stable products, 2_X-Z. In IRC calculations that were shown in Paths 1 and 2, C₆–N₁ bond was cleavage, before reaching reaction rate determinating step (transition state).     

Photodecomposition of molybdenum(II) and tungsten(II) carbonyl complexes with triazole, benz-imidazole, and oxadiazole acetylinic derivatives

Photodecomposition of 10 different molybdenum and tungsten mixed carbonyl complexes, [M(CO)₃(B)(A)]I₂ where B=o-phenanthroline or bipyridyl, A=3-(2-propynyl)thio-4,5-diphenyl-4H-1,2,4-triazole (TRZA) or S-propynyl-2-thio benz-imidazole (BIMDA) and 2(2-propynyl-thio(5-phenyl)-1,3,4-oxadiazole (OXA). M(CO)₃(TRZA)I₂, [M(CO)₂(PPh₃)_X(TRZA)I_Y]I_Z where M=Mo, X, Y and Z=1 and M=W, X and Z=2, Y=0, have been performed at 365 nm in oxygen saturated chloroform at 25 °C. The absorbance spectrum of these complexes have been recorded with the time of irradiation in order to examine the kinetics of photodecay.

The apparent rate constant (K_d) for the first-order reaction have been calculated and found to be (3.32–4.79)×10⁻⁵ s⁻¹. The primary quantum yields (Φ) has also been calculated and were in the range (8.33–12.1)×10⁻⁴. The mechanism of the photodecomposition has been suggested according to the kinetic, and photoproduct analysis data, and is similar to reaction of photo-oxidative degradation of polluted molecules in the water.     

Ab initio molecular orbital study of Fe2Cl6 and FeAlCl6

Ab initio molecular orbital theory was used to determine the equilibrium structure and vibrational frequencies of Fe₂Cl₆ and FeAlCl₆. The equilibrium structure the Fe₂Cl₆ dimer has D_2h symmetry with a planar arrangement of the four membered {FeCl_brFeCl_br} ring, similar to the Al₂Cl₆ dimer. The calculated bond distances and vibrational frequencies are in good agreement with experiment. The potential energy surface for the puckering of the {FeCl_brFeCl_br} ring is extremely flat. This prevents an unambiguous assignment of either D_2h or C_2v symmetry to the Fe₂Cl₆ structure in electron diffraction measurements. The FeAlCl₆ molecule is found to have a C_2v structure similar to Fe₂Cl₆ with vibrational frequencies in good agreement with experiment.     

On the multiple peaks in charge-transfer probability versus laser frequency in the theory of laser assisted surface ion neutralization

Some aspects of the theory of LASIN (laser assisted surface ion neutralization) are discussed, with emphasis on the physical origins of the so-called double-peak structures found in some calculations of the charge-transfer (neutralization) probability, P, as a function of the laser frequency η. These two peaks have been called the first peak at η ≈ η_m = _O − _m (in a.u.), where _o(_m) is the electronic energy level of the ion/atom (middle of the solid's valence band) and the second peak, a much larger peak at η ≈ 1.3 η_m, respectively.

We show that these double-peak structures are all special cases of multiple-peak structures which result from quantum interference effects, and that, in fact, the second peak is to be regarded as the main resonance peak. This result is interesting in itself, because it is the first peak which has heretofore been considered the main resonance peak.

To simplify the discussion, a two-level model is adapted, which represents the solid valence band by a single level at _m. Clarification of the physical reason for the multiple peaks is based on the semiclassical theory of nonadiabatic transitions, in which the peaks are due to the phase difference between the two adiabatic paths that arise from the diagonalization of the two-level hamiltonian.

With the electronic hopping potential modelled by V(t) = V_osech(λt), and the laser potential by W(t) = W_osech(λt) cos(πt + δ), in the usual notation, an approximate analytical expression for P(η) is presented for the case W_o/V_o < 1, which covers most of the previous treatments, and is in good agreement with the exact results.     

Ab initio study on the kinetics and mechanisms of the formation of Agn (n = 2–6) clusters

The CCSD(T)/11e-RECP//MP2/11e-RECP method was used to explore the potential energy surfaces (PESs) of the formation of Ag_n (n = 2–6) clusters. Two kinds of reaction mechanisms were revealed in the formation of Ag_n clusters, the association mechanism for the formation of Ag₂, Ag₅, and Ag₆ clusters and the association–isomerization mechanism for the formation of Ag₃ and Ag₄ clusters. Based on the canonical transition state theory, the calculated rate constants of the formation of Ag_n clusters displayed an odd–even effect: the rate constants of formation of Ag_n clusters with odd number were larger than those with even number. The rate constant of formation of Ag₄ was the lowest, whereas that of Ag₅ was the highest among Ag_n (n = 2–6) clusters. The formation of Ag₄ was the most difficult step in the aggregation process of the silver clusters. The formation of Ag₄ may be related with the critical point in the silver aggregation process.     

Density functional theory analysis of CaRgn complexes: (Rg=He, Ne, Ar; n=1–4)

CaRg_n⁺ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe_n⁺ (n=1–4) complexes are found to be stable. In the case of CaNe_n⁺ and CaAr_n⁺, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C_3V and the D_3h point group as well as for n=4 in the T_d (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface.     

Substantial velocity dependence of rotationally inelastic collision cross sections in Li2—Xe

A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ_ji,Δ(ν_r) for rotationally inelastic collisions from level j_i to j_i + Δν₁ = 8,22,42) in ⁷Li^*₂ A ¹Σ⁺_u)—Xe. The σ_jν^±2(ν_r) are strongly attenuated at a smaller ν_r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ_jiΔ = ν_r⁻ⁿ (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited.     

Stabile Bis(η-alkin)MCl2-komplexe; Darstellung und reaktivität

The synthesis and reactivity of {(η⁵-C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂} MCl₂ (M = Fe: 3a; M = Co: 3b; M = Ni: 3c) is described. The complexes 3 are accessible by the reaction of (η⁵-C₅H₄SiMe₃) ₂Ti(CSiMe₃)₂ (1) with equimolar amounts of MCl₂ (2) (M = Fe, Co, Ni). 3a reacts with the organic chelat ligands 2,2′-dipyridyl (dipy) (4a) or 1,10-phenanthroline (phen) (4b) in THF at 25°C to afford in quantitative yields (η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂ (1) and [Fe(dipy)₂]Cl₂ (5a) or [Fe(phen)₂]Cl₂ (5b). 1/n[Cu^IHal]_n (6) or 1/n[Ag^IHal]_n (7) (Hal = Cl, Br) react with {(η⁵ -C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂}FeCl₂ (3a), by replacement of the FeCl₂ building block in 3a, to yield the compounds {(η⁵-C₅H₄SiMe₃)₂Ti(C CSiMe₃)₂}Cu^IHal (8) or {(η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂}Ag^IHal (9) (Hal = Cl, Br), respectively. In 8 and 9 each of the two Me₃SiCC-units is η²-coordinated to monomeric Cu^I Hal or Ag^IHal moieties. Compounds 8 and 9 can also be synthesized by the reaction of (η⁵-C₅H₄SiMe₃)₂ Ti(CSiMe₃)₂ (1) with 1/n[Cu^IHal]_n (6) or 1/n [Ag^IHal]_n (7) in excellent yields. All new compounds have been characterized by analytical and spectroscopic data (IR, ¹H-NMR, MS). The magnetic moments of compounds 3 were measured.     

Si-Kernresonanzspektren und synthese von bromdisilanen und ioddisilanen

The syntheses of Bromodisilanes Br_nSi₂H_6−n and Iododisilanes I_nSi₂H_6−n (n = 1, 2, 3, 4, 5), starting from caryldisilanes Ar_nSi₂H_6−n (Ar = phenyl, -naphthyl, mesityl) are reported. The ²⁹Si-NMR-spectra of all compounds, including ²⁹Si²⁹Si-coupling constants, have been measured.

Zusammenfassung

Ausgehend von Aryldisilanen ArS₂H_6−n, (Ar = Phenyl, -Naphthyl, Mesityl) wurden die Bromdisilane Br_nSi₂H_6−n, und Ioddisilane I_nSi₂H_6−n, (n = 1, 2, 3, 4, 5) synthetisiert. Die ²⁹Si-NMR-Spektren aller Verbindungen, (eingeschlossen ²⁹Si²⁹Si-Kopplungskonstanten) wurden vermessen.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Synthesis of ferrocenyl-1,2-diketones and related compounds: Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione

Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C₅H₅)Fe(C₅H₄)] can be prepared by oxidation of acylferrocenes FcCOCH₂R or, more efficiently, by oxidation of the isomeric ketones FcCH₂COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH₂PPh₃)⁺I⁻ via the acylated salts [FcCH(COR)PPh₃]⁺I⁻. The haloacylferocenes FcCOCCl_x H_3−x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel—Crafts acylation of ferrocene using CCl_xH_3−xCOCl/AlCl₃, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl_xH_3−x and the other giving the reduced products FcCOCCl_x−1H_4−x. Two diketones FcCOCOFc 3b and FcCOCOC₆H₄Ph 3c have been structurally characterised by single-crystal X-ray diffraction.     

Structure and redox properties of CexPr1−xO2−δ mixed oxides and their catalytic activities for CO, CH3OH and CH4 combustion

A series of Ce_xPr_1−xO_2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH₃OH and CH₄ on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO₂ was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO₂ crystal lattices. Raman bands at 465 and 1150 cm⁻¹ in Ce_xPr_1−xO_2−δ samples are attributed to the Raman active F_2g mode of CeO₂. The broad band at around 570 cm⁻¹ in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm⁻¹ may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr₆O₁₁ shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce_xPr_1−xO_2−δ mixed oxides is lower than those of Pr₆O₁₁ or CeO₂. TPR results indicate that Ce_xPr_1−xO_2−δ mixed oxides have higher redox properties because of the formation of Ce_xPr_1−xO_2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH₃OH oxidation, while the activity of CH₄ oxidation is mostly related to reduction temperatures and redox properties.     

The molecular structure of beryllocene, (C5H5)2Be. A reinvestigation by gas phase electron diffraction

The electron scattering pattern of gaseous dicyclopentadienylberyllium, Cp₂Be, has been recorded from s = 2.00 to 39.00 Å⁻¹ with a nozzle temperature of about 120°C. Molecular models of D_5d symmetry or models containing one π-bonded and one σ-bonded Cp ring are not compatible with the data. The possibility the gaseous Cp₂Be consists fo a mixture D_5d and π-Cp, σ-Cp conformers is considered and rejected. A model of C_5v symmetry can be brought into satisfactory agreement with the data. It is also found that a slip sandwich model obtained from the C_5v model by moving sideways the ring which is at the greatest distance from Be, while keeping the two rings essentially parallel is compatible with the electron diffraction data. The best fit between experimental and calculated intensity curves is obtained with a model with a sideways slip of 0.8(1) Å. This model is similar to that indicated by the X-ray diffraction investigations by Wong and coworkers [4,5]. It is suggested that the potential energy of the molecule does not change much as the magnitude of the slip changes and that the molecule thus undergoes large amplitude vibration.     

Structural, spectral and thermal properties of a polymeric nickel(II) complex containing two-dimensional network

The structure of the complex [Ni(hmt)(NCS)₂(H₂O)₂]_n, assembled by hexamethylenetetramine (hmt) and octahedral Ni(II), is reported. Crystal data: Fw 351.07, a=9.885(10) Å, b=12.06(1) Å, c=12.505(8) Å, β=114.41(4)°, V=1357(1) ų, Z=4, space group=C2/c, T=173 K, λ(Mo−K)=0.71070 Å, ρ_calc=1.718 gcm⁻¹, μ=17.44 cm⁻¹, R=0.099, Rw=0.145. The tetrahedral assembling template effect of the hmt molecule is completed by two coordination bonds and two hydrogen interactions. The UV–vis absorption spectrum of this complex [Ni(hmt)(NCS)₂(H₂O)₂]_n with a two-dimensional network is determined in the range of 5000–35000 cm⁻¹ at room temperature. The observed spectrum is discussed and explained perfectly by the scaling radial theory proposed by us. The two-dimensional structure has no apparent effects on the d–d transitions of the central Ni(II) ion. The IR spectrum and the GT curve of the complex were also measured and clearly reflect its structural properties.