Ab initio MRD-CI study of GaAs, GaAs2(±), Ga2As2(±) and As4 clusters

Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As₂^(±), As₄⁽⁺⁾, GaAs⁻, GaAs₂^(±) and Ga₂As₂^(±). This study complements previous theoretical investigations on Ga^(±) to Ga₄^(±) and GaAs⁽⁺⁾. For As₄ tetrahedral symmetry was assumed, and Re of X¹A₁ determined as 4.73a₀. Vertical ionization potentials to several states of As₄⁺ were calculated. For GaAs₂, GaAs₂⁺ and GaAs₂⁻, ground and one low-lying state were geometry-optimized, both in C_2v (Ga-As-As), and linear symmetry (GaAsAs, C_∞h and AsGaAs, D_∞h). The lowest state of GaAs₂ is ²B₂ in C_2v. For Ga₂As₂, the lowest state and low-lying excited states were optimized in various geometries. The most stable state has rhombic structure (¹A_g in D_2h), but T-form and other forms (C_2v, C_∞v, D_∞h) are only 1–2 eV less stable. In D_2h symmetry, several low-lying excited states of Ga₂As₂ were studied. The ground states of Ga₂As₂⁺ and Ga₂As₂⁻ were found to be ²B_2u, and ²B_2g, respectively. Trends in ionization potentials (IP), electron affinities (EA), atomization energies and fragmentation energies for the molecules Ga_xAs_y and the pure compounds Ga_n and As_n up to 4 atoms, were studied. Ga_xAs_y clusters, with x + y even, have higher IP's than odd-numbered clusters. An experimentally observed alternation of EA, whereby an odd number of atoms have higher EA than their even neighbors, is confirmed. The mixed compounds Ga_xAs_y have atomization energies between those of Ga_n and As_n (x + y = n), usually closer to those of Ga_n. Fragmentation of Ga_xAs_y occurs such that As----As bonds are retained, and if possible, also Ga----As bonds, since the dissociation energy of As₂ is higher than that of GaAs, which in turn is higher than that of Ga₂. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga_xAs_y.     

Testing the uncertainty principle using (n,γ) photon beams and pulsed neutron beams

Nuclear resonance scattering of a photon beam based on the (n,γ) reaction was used for measuring the mean square zero-point linear momenta p_a² and p_c² of the atoms of a metallic Zn single crystal. A similar measurement was carried out using a pulsed neutron source. These were combined with corresponding values of x_a² and x_c² obtained using the Mössbauer effect. In both the cases the measured values of p_a² and p_c² were found to conform to the requirements of the Uncertainty principle for a real solid to within 3%.     

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.     

Thermodynamics of (1,4-difluorobenzene + an n-alkane) and of (hexafluorobenzene + an n-alkane)

Excess molar enthalpies H^E and excess molar volumes V^E have been measured, as a function of mole fraction x₁, at 298.15 K and atmospheric pressure for the five liquid mixtures (x₁1,4-C₆H₄F₂ + x₂n-C_lH_2l+2), l = 7, 8, 10, 12 and 16. In addition, H^E and excess molar heat capacities C_P^E at constant pressure have been determined for the two liquid mixtures (x₁C₆F₆ + x₂n-C_lH_2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the H^E version was equipped with separators) and a vibrating-tube densimeter, respectively.

The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from H^E(x₁ = 0.5)/(J mol⁻¹) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes V^E are all positive and also increase with increasing l: V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x₁C₆F₆ + x₂n-C_lH_2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C₆H₄F₂. Specifically, at 298.15 K H^E(x₁ = 0.5)/(J mol⁻¹) = 1119 for (x₁C₆F₆ + x₂n-C₇H₁₆) and 1324 for (x₁C₆F₆ + x₂n-C₁₄H₃₀), and for the same mixtures V^E(x₁ = 0.5)/(cm³ mol⁻¹) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): C_P^E(x₁ = 0.5)/(J K⁻¹ mol⁻¹) = −1.18 for (x₁C₆F₆ + x₂n-C₇H₁₆), and −2.25 for (x₁C₆F₆ + x₂n-C₁₄H₃₀). The curve C_P^E vs. (x₁ for x₁C₆F₆ + x₂n-C₁₄H₃₀) shows a sort of “hump” for x₁ 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures.     

First principles study of the structure, electronic state and stability of AlnPm cations

Structural and electronic properties of semiconductor binary microclusters Al_nP_m⁺ cations have been investigated using the B3LYP–DFT method in the ranges of n=1,2 and m=1–7. Full structural optimization, adiabatic ionization potentials calculation and frequency analysis are performed with the basis of 6-311G(d). The charge-induced structural changes in these cations have been discussed. The strong P–P bond is also favored over Al–P bonds in the Al_nP_m⁺ cations in comparison with corresponding neutral cluster. With P_m forming the base, adding Al atom(s) in different positions would find the stable structures of Al_nP_m⁺ cations quickly and correctly. Both AlP₄⁺ and AlP₆⁺ are predicted to be species with high stabilities and possible to be produced experimentally.     

Ligand deprotonation significance in the formation of the molybdate ion-malic acid complexes

Using the temperature jump technique, the study of the kinetics of the complexing of oxomolybdate anion with malic acid has been carried out in aqueous solutions of pH 7.15–8.5 at ionic strength 0.1 M (KNO₃) and 25°'C. A reaction scheme for the formation of 1 : 1 complexes is proposed which accounts for the observed relaxation rates.

The significance of the ligand deprotonation on the complexation reaction of MoO₄²⁻ by a single protonated ligand, i.e. MoO₄²⁻+LH^nk→MoO₃(OH)Lⁿ⁻², (where n = 1 -, 2 -, etc), is analysed on the basis of a simple model. A linear correlation between the log k and the pK of the monoprotonated ligand (LH) is found for this reaction when the global process is controlled by the proton transfer from the ligand to an oxogroup, i.e. log k = a - 0.5xpK. It is found that this correlation is satisfied by MoO₄²⁻ and WO₄²⁻. The experimental slopes for these oxyanions are −0.503 and −0.543 respectively, in agreement with the predictions.     

Pathway studies in the fragmentation of Ge(CH3)4 involving Ge(3d,3p,3s) and C(1s) inner-shell photoexcitation in the range 49.5–450 eV

The dissociative multiple photoionization of tetramethylgermane (Ge(CH₃)₄) in the valence, and in the Ge(3d,3p,3s) and C(1s) inner-shell regions has been studied by using time-of-flight mass spectrometry coupled to synchrotron radiation in the range 49.5–450 eV. Total and individual photoion yields have been recorded as a function of the incident photon energy. Several discrete resonances over a structureless giant resonance are observed below the Ge(3p), Ge(3s) and C(1s) threshold regions. The structureless giant resonance corresponding to the Ge(3d) presumably arises from the continuum enhancement caused by the 3d→εf transition. Various monocations of H⁺, H₂⁺, CH_n⁺ (n=0–4), C₂H_n⁺ (n=0–5), GeH_n⁺, GeCH_n⁺, GeC₂H_n⁺, and GeC₃H_n⁺ are detected in the whole energy range. Dissociation processes have also been investigated by photoelectron–photoion and photoion–photoion coincidence methods. The dominant dissociation channel is found to be CH_n⁺–GeCH_n⁺ in the whole energy examined. Specific energy dependence of dissociation processes is observed in the Ge(3p) and Ge(3s) regions. With the help of ab initio HF/6-311++G(2df,p) calculation, we roughly estimated the photoabsorption positions and symmetries for the discrete core hole states.     

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.     

杂多酸/离子液体杂化材料催化苯的高选择性羟基化

制备了V取代的磷钼酸H_3+xPMo_12-xV_xO₄₀（x=0,1,2）及1-丁基-3-甲基咪唑溴盐离子液体（[C₄mim]Br）,并采用离子交换的方法制备了系列杂化材料（[C₄mim]3+xPMo_12-xV_xO₄₀,x=0,1,2）;采用X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）、紫外-可见漫反射光谱（UV-Vis DRS）对所制备样品进行了表征;以H₂O₂为氧化剂,考察了所得样品催化苯羟基化制苯酚的活性。结果表明,和相应的离子液体及杂多酸相比,杂化材料的催化活性得到了很大的提高,尤其是催化剂[C₄mim]₅PMo₁₀V₂O₄₀,在优化后的条件下,苯的转化率可达到21%,苯酚的选择性在99%以上。而且,该催化剂具有很好的可重复使用性,连续使用五次后,苯的转化率和苯酚的选择性没有明显降低。     

确定分子中离域π键πnm的方法

A method for obtaining the delocalized π bonds π_n^m in a molecule has been discussed in this paper, and the delocalized π bonds π_n^m in linear, bent, planar trigonal, single cyclic conjugated, and polycyclic conjugated molecules have been studied. The reasons of π₃⁴ in NO₂ and 2π₃² in C₃ molecules have been proposed. The delocalized π bonds 2π₁₈¹⁸ in cyclo[18] carbon are analyzed.     

Formation of [C60C5H5] adduct cations and theoretical study of the isomers

We study here the reactions between C₆₀ and planar C₅H₅⁺ cations that lead to the formation of [C₆₀C₅H₅]⁺ adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C₆₀C₅H₅]⁺: σ-adduct, π-complex, [1,4]- and [l,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the σ-addition cation. Another interesting and stable structure is the π-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Å with the C_5v symmetry. The C₅H₅⁺ cyclopentadienium cation seems to be an “inverted umbrella” sitting on a five-membered ring of the C₆₀ cage.     

Vibration-rotation spectra of C containing acetylene: anharmonic resonances

High resolution vibration-rotation spectra of ¹³C₂H₂ were recorded in a number of regions from 2000 to 5200 cm⁻¹ at Doppler or pressure limited resolution. In these spectral ranges cold and hot bands involving the bending-stretching combination levels have been analyzed up to high J values. Anharmonic quartic resonances for the combination levels ν₁ + mν₄ + nν₅, ν₂ + mν₄ + (n + 2) ν₅ and ν₃ + (m − 1) ν₄ + (n + 1) ν₅ have been studied, and the l-type resonances within each polyad have been explicitly taken into account in the analysis of the data. The least-squares refinement provides deperturbed values for band origins and rotational constants, obtained by fitting rotation lines only up to J ≈ 20 with root mean square errors of ≈ 0.0003 cm⁻¹. The band origins allowed us to determine a number of the anharmonicity constants x_ij⁰.     

A “vertex electron pair” scheme (VEPS) for describing the skeletal electron distribution in borane-type clusters

A predominantly localized electron pair scheme is outlined for describing the electron distribution and bonding in closo borane anions B_nH_n²⁻ and related electron deficient deltahedral clusters, in which a skeletal electron pair is assigned to each vertex, one pair being regarded as delocalized just inside the roughly spherical surface on which the skeletal atoms lie. The scheme gives a clearer picture of the electron distribution than is conveyed by resonating 2- and 3-centre bonds in the polyhedron edges and faces, and allows the bond orders of the polyhedron edge links to be calculated readily. The consequence of formal removal of BH²⁺ units from closo species B_nH_n²⁻ to generate nido species B_n−1H_n−1⁴⁻ and arachno species B_n−2H_n−2⁶⁻ is explored, and seen to allow rationalization of two features of such deltahedral-fragment clusters: (i) why a high-connectivity vertex is left vacant and (ii) why the frontier orbitals of such species concentrate electronic charge around their open faces. Moreover, in the case of D_4‘h B₄H₄⁶⁻ (cf. C₄H₄²⁻) and D_5h B₅H₅⁶⁻ (cf. C₅H₅⁻), the approach leads directly to the familiar picture for aromatic ring systems in which the highest filled, doubly degenerate π-bonding molecular orbital concentrates electronic charge in rings above and below the polygon on which the skeletal nuclei lie. It also leads to the expectation that arachno clusters with non-adjacent vacant vertices will be more stable than those with adjacent vacant vertices.     

[(Me3Sn)2(Me3Sb)M(CN)6]∞ (M = Fe, Ru): Neuartige Organo-Sn/Sb-Polymere von besonderer chemischer und thermischer stabilität

The thermally (decomp. temp. 300°C) and completely air stable, novel coordination polymers [(Me₃Sn^IV)₂(Me₃Sb^V)M^II(CN)₆]_∞ with M = Fe and Ru can be prepared by co-precipitation from aqueous solutions of Me₃SnCl, Me₃SbBr₂ and K₄[(M(CN)₆], or, alternatively, by the ion-exchange-like reaction of the polymers [A(Me₃Sn)₃M(CN)₆]_∞ (A⁺ = Et₄N⁺, Cp₂Co⁺, Me₃Sn⁺ etc.) with Me₃SbBr₂. IR-spectroscopic findings suggest a statistical distribution of quasi-octahedral M(CN-Sn··)_6-x(CNSb ··)_x building blocks (with x = 0–6) within a three-dimensional network.     

Oxygen abstraction from tetrahydrofuran by molybdenum-iodide complexes. X-ray molecular structure of [Mo2(μ-O)(μ-I)(μ-O2CCH3)I2(THF)4][MoOI4(THF)] (THF = tetrahydrofuran)

The interaction between Mo₂(O₂CCH₃)₄, Me₃SiI and I₂ in THF resulted in oxygen abstraction from the solvent and formation of [Mo₂(μ-O)(μ-I)(μ-O₂CCH₃) I₂(THF)₄]⁺[MoOI₄(THF)]⁻ and I---(CH₂)₄---I. The molybdenum complex has been characterized by X-ray diffractometry. Crystal data: triclinic, space group P , a = 13.827(3) Å; b = 15.803(7) Å; c = 9.950(3) Å; = 93.34(4)°; β = 102.40(2)°; γ = 90.09(2)°; V = 2120(2) Å₃; Z = 2; d_calc = 2.559 g cm⁻³; R = 0.0476 (R_w = 0.0613) for 370 parameters and 3938 data with F₀²> 3σ(F₀²). The metal-metal distance in the cation is 2.527(2) Å and indicates a strong interaction. The magnetic behavior is consistent with the assignment of one unpaired electron to the Mo₂⁷⁺ core of the cation and one to the d¹ Mo(V) center of the anion. The interaction between Mo(CO)₆ and I₂ in THF also results in the formation of 1,4-diiodobutane.     

1-乙基-3-甲基咪唑丙氨酸离子液体热力学性质的研究

用中和法合成了氨基酸离子液体1-乙基-3-甲基咪唑丙氨酸([C₂mim][Ala]),并利用恒温环境的溶解反应热量计,在(288.15±0.01) K-(308.15±0.01) K温度范围内每隔5 K,测定不同质量摩尔浓度离子液体在水中的溶解焓(Δ_solH_m^θ).根据Archer的方法,通过线性拟合得到了该离子液体的标准摩尔溶解焓(Δ_sol),并计算了其相对表观摩尔溶解焓(^ΦL).在298.15 K下,根据Glasser经验方法得到了格子能U_POT = 566 kJ·mol^-1,并计算了其阴阳离子水化焓值(ΔH⁺ + ΔH^-) = -620 kJ·mol^-1及阴离子水化焓ΔH^-([Ala]^-) = -387 kJ·mol^-1.此外,估算了[C₂mim][Ala]水溶液的热容(C_p(sol))和表观摩尔热容(^ΦC_p).     

Synthesis and low temperature fluorination of the alkaline-earth palladates Ba2−xSrxPdO3 (x = 0–2)

Since the discovery of superconductivity in Sr₂CuO₂F_2+δ there has been an increased interest in ternary oxide-fluorides. Sr₂CuO₂F_2+δ is prepared via low temperature (T = 220 °C) reaction routes. Low temperature fluorination induces an interesting structural rearrangement in the parent compound Sr₂CuO₃, which is a one-dimensional material containing linear chains of vertex sharing CuO₄ squares along the crystallographic b axis. Upon fluorination, one oxide is substituted by two fluorides and Cu²⁺ becomes octahedrally coordinated by four oxides and two fluorides. The fluorinated compound Sr₂CuO₂F_2+δ displays the T-type structure (La₂CuO₄). Insertion of excess fluorine, δ, also takes place and this fluorine occupies interstitial sites in the T structure. Although the starting material Ca₂CuO₃ is isostructural to Sr₂CuO₃, Ca₂CuO₂F_2+δ displays the T′ (Nd₂CuO₄) structure due to the smaller radius of Ca²⁺ compared to that of Sr²⁺.

The alkaline-earth palladates with the general formula A₂PdO₃ (A = Ba, Sr) are isostructural with the A₂CuO₃(A = Ca, Sr) materials. We prepared the Ba_2−xSr_xPdO₃ (x = 0–2) series and performed low temperature fluorination, which led to the synthesis of the series Ba_2−xSr_xPdO₂F_2+δ (0 ≤ x ≤ 1.5). All the compounds in the Ba_2−xSr_xPdO₂F_2+δ series show T′ structure (Ca₂CuO₂F_2+δ). Similarities and differences with Sr₂CuO₂F_2+δ and Ca₂CuO₂F_2+δ will be discussed.     

铂钌团簇及电荷对甲醇活性的理论研究

采用密度泛函理论(DFT)对钌掺杂的铂团簇阳离子([Pt_nRu_m]⁺, m + n = 3, n ≥ 1)活化甲醇C―H和O―H键反应进行了理论研究;探讨了电荷对[Pt_nRu_m]团簇反应活性的影响。电荷分析表明:(1) [Pt₃]⁺团簇中正电荷在三个Pt原子上均匀分布;掺杂Ru原子后,正电荷主要分布在Ru原子上; (2)首先活化C―H键时[Pt_nRu_m]⁺的反应活性比[Pt_nRu_m]明显提高;首先活化O―H键时只有[Pt₃]⁺比[Pt₃]团簇的反应活性有明显提高。本研究可为金属团簇调控的C―H键和O―H键的活化提供更深入的理解。     

一个各向异性磁稀释杂化钙钛矿系列[CH3NH3][CoxZn1-x(HCOO)3]

Inorganic-organic or hybrid perovskite materials, which are the complementary counterparts of pure inorganic perovskites, can provide many new opportunities in the researches of phase transitions, critical phenomena, and relevant properties, as they combine the characteristics of inorganic and organic components. Therefore, the hybrid perovskites of ammonium metal formate framework are very promising, and their properties have been found to be strongly dependent on the characteristics of the constituent metal ions and/or ammonium ions. Herein, we used solid solution strategies, borrowed from solid state chemistry, to investigate the anisotropic diluted magnetic hybrid perovskite system of [CH₃NH₃][Co_xZn_1-x(HCOO)₃], wherein the B-sites are occupied by the mixed metal ions of Co²⁺ and Zn²⁺. The solid solution compounds of this series in the range x = 0–1 (or the molar percent Co% = 0–100%) were successfully prepared using conventional solution chemistry methods. The resulting compounds were demonstrated to be iso-structural by using both single-crystal and powder X-ray diffraction analyses. The solid solution crystals belong to the orthorhombic space group Pnma, with the cell parameters being a = 8.3015(2)–8.3207(3) Å, b = 11.6574(4)–11.6811(5) Å, c = 8.1315(3)–8.1427(4) Å, and V = 787.89(5)–790.98(7) ų. The perovskite structure consists of a simple cubic anionic metal-formate framework and CH₃NH₃⁺ cations which are located in the framework cavities, with N―H···O hydrogen bonds formed between the framework and the cation. The members of this series showed negligible changes (< 0.4%) in their respective lattice and structural parameters. Thus, the prepared solid solution compounds constitute good molecule-based examples for the study of magnetic dilution under almost the same structural parameters and molecular geometries. Upon dilution, the magnetization per mole of Co at low temperatures and low fields was suppressed by the magnetic anisotropy of Co²⁺ and gradual destruction of the large spin canting between coupled Co²⁺ ions, in contrast to the magnetization enhancement observed in the isotropic diluted system of [CH₃NH₃][Mn_xZn_1-x(HCOO)₃] with the same perovskite structure. The percolation limit was estimated as (Co%)_P = 27(1)% (or x_P = 0.27(1)) from the magnetic data, which was slightly lower than that predicted by the percolation theory for a simple cubic lattice (31%); this trend was due to the strong magnetic anisotropy of the present system. In addition, rare incommensurate phase transitions were primarily detected below ~120 K for the pure Co and Zn members, which may also affect the magnetic properties of the materials.