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1.
《Chemical physics letters》1987,133(6):525-530
Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO and DCO to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO and DCO.  相似文献   

2.
A novel fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by 1H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO32? and HCO3? addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.  相似文献   

3.
Carbocuprate compounds are generally described as multiple perovskites with CO 3 2 - and Cu-O alternating layers containing Ba and/or Sr; they have gained an unexpected importance in the high temperature superconductivity field, because many compounds with transition temperature above 100 K belong to this class of materials.We have started a systematic study on phase formation and stabilisation in the Ba-Cu-C-O system in the temperature range 20-600°C, by using thermal analysis techniques. Starting from a BaCO3-BaO2-CuO mixture (311 mol), a new phase isomorphic with BaCO3 formed after heat treatment above 390°C in air. TG, DSC, EGA and high temperature XRD were employed to follow the complex interaction of the reactants with the atmosphere and the formation of the new phase.  相似文献   

4.
As first noted by Dixon et al. (J Am Chem Soc 108:2461–2462, 1986), heavily fluorinated pyramidal phosphorus compounds, e.g., F n PH(3?n) with n > 1, invert through a T-shaped transition state (edge inversion) rather than the D3h-like transition states (vertex inversion) found in the corresponding nitrogen compounds and less fluorinated phosphorus compounds. Subsequent studies by Dixon and coworkers established that this is a general phenomenon and has important chemical consequences. But what is the reason for the change in the structure of the transition state? Recent theoretical investigations have resulted in the discovery of a new type of chemical bond, the recoupled pair bond. In particular, it was found that recoupled pair bond dyads account for the hypervalency of the elements beyond the first row. In this paper, we show that recoupled pair bond dyads also account for the existence of the edge inversion pathway in heavily fluorinated phosphorus compounds and likely account for the presence of the lower energy inversion pathways in pyramidal compounds of other elements beyond the first row.  相似文献   

5.
《Chemical physics letters》1987,141(5):455-458
Large basis set ab initio Hartree-Fock calculations of the energetics of the model reaction Mn (H)(CO)→Mn(HCO) are reported. The use of polarization functions in the ligand atom basis sets has a profound effect upon the energetics of this isomerization reaction.  相似文献   

6.
合成了系列新化合物RE(HCO2)3(HNO2)(H2CO2)(RE=Y,Tb,Dy,Ho,Er,Yb,Tm),用X射线方法表征了其结构。单晶结构分析表明此新类型的结构为正交晶系且具有非中心对称空间群(20)C2221,晶体结构为三维网络结构,结构的...  相似文献   

7.
Reversible catalysis is a hallmark of energy-efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition-state barriers. Using these criteria, we demonstrate reversible CO2/HCO2 conversion catalyzed by [Pt(depe)2]2+ (depe=1,2-bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO2 reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO2 reduction, H2 evolution is negligible and the Faradaic efficiency for HCO2 production is nearly quantitative. A free-energy analysis reveals H2 evolution is endergonic, providing a thermodynamic basis for highly selective CO2 reduction.  相似文献   

8.
The Zintl anion (Ge2As2)2− represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh3)AuMe] into the 1,2-diaminoethane (en) solution of (Ge2As2)2−, the heterometallic cluster anion [Au6(Ge3As)(Ge2As2)3]3− is obtained as its salt [K(crypt-222)]3[Au6(Ge3As)(Ge2As2)3]⋅en⋅2 tol ( 1 ). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non-bonding) octahedron of six Au atoms that is face-capped by four (GexAs4−x)x (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge3As)3− unit besides three (Ge2As2)2− units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au6(Ge3As)(Ge2As2)3]3−. Reactions of the heavier homologues (Tt2Pn2)2− (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1 , but dimers of ternary nine-vertex clusters, {[AuTt5Pn3]2}4− (in 2 – 4 ; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo-tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge2As2)2−, according to the DFT calculations.  相似文献   

9.
Alkali metals are generally Lewis acids. On the contrary, Lewis basic character of alkali metals forming donor – acceptor complexes is a very rare phenomenon. In this contribution, I have theoretically designed an anionic cluster MMN3 (M=alkali metals) on the basis of experimentally known reagent, alkali salt of azide ion MN3, which shows unprecedented M:→M donor-acceptor interaction. To the best of author's knowledge, the characterization of such donor-acceptor interaction among alkali metals is unprecedented. Formation of the 2c–2e donor-acceptor bonds have been confirmed by quantum theory of atoms in molecules and electron localization function analyses. The calculated bond dissociation energies are significant suggesting their possible spectroscopic identification.  相似文献   

10.
《Chemical physics》1987,115(3):423-432
The dissociation energy (De) for the O3(X̃ 1A1) → O2(X 3Σg) + O(3P) process is computed using MC SCF, CI, MBPT, and CCD methods. A full-valence MC SCF calculation utilizing a [9s5p3d1f/5s3p2d1f] basis set yields a De value of 0.43 eV, far below the experimental value of 1.13 eV, demonstrating the importance of correlation effects involving non-valence orbitals. A CI calculation in the same basis set allowing for all single and double excitations from three-reference configuration yields a De value of 0.72 eV. This value is increased to 1.06 eV when the Davidson correction is included. When the number of reference configurations is increased to eight, the resulting CI calculation gives a De value of 0.82 eV prior to the Davidson correction and 1.10 eV after this correction.  相似文献   

11.
Poly (vinyl alcohol) (PVA)–functionalized β-cyclodextrin (β-CD) polymer crosslinked by citric acid (PVA-g-CD) was synthesized, characterized and evaluated for the catalytic oxidation of cinnamaldehydes. The polymer showed good activity and selectivity to aldehydes for some structurally diverse cinnamaldehydes. The enhanced catalytic activity may be attributed to the synergistic effect of the intermolecular weak interactions between β-CD and the functional group of PVA. In addition, calcium peroxide as a solid oxidant was found to significantly affect the reaction. This catalyst can be recovered and reused for five times without a significant loss in its activity and selectivity.  相似文献   

12.
An electron diffraction and microscopy study of the CaFexMn1−xO3−y system treated at 1100°C in air has been performed. An increase of y is accompanied by an increase of the cubic perovskite substructure parameter, the nonstoichiometry being accommodated in several ways. The system contains two solid solutions of the perovskite-type (P) and of the brownmillerite-type (B) and also an intermediate phase (x = 0.6) which makes disordered intergrowth with the B-type solid solution. These results are discussed in terms of multitwinning, randomly dispersed oxygen deficiency, and ordered and disordered intergrowth formation.  相似文献   

13.
Summary The question of the hybridization of the atomic orbitals of Mo in the Mo(CN)8 4– ion is examined, and it is shown that the dodecahedral structure can exist without the participation off electrons.  相似文献   

14.
The preparation and densification (95 %) of ceramics of the new solid solution LaGa1−xNixO3−δ have been carried out for x ≤ 0.50. The chemical analysis of the materials shows that both the oxygen nonstoichiometry amount (δ) and the electron carrier concentration increase with the substitution of nickel for gallium. Whereas LaGaO3 is an insulator, the Ni-doped phases are semi-conducting and behave as a metal for the highest nickel contents. The dilatometric features versus temperature show these materials to be mechanically compatible with the electrolyte La0.90Sr0.10Ga0.80Mg0.20O2.85. In addition their chemical composition does not change at high temperature. All these characteristics make these materials good candidates as cathodes for solid oxide fuel cells.  相似文献   

15.
Various compositions (1−x)BaTiO3 + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba1−x Pb x (Ti1−x Li x ) O3−3x F3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 107 Hz). The dielectric performances are the best for ceramic Ba0.97Pb0.03(Ti0.97Li0.03)O2.91F0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.   相似文献   

16.
Stoichiometric four-layered hexagonal (4H) (Sr1?x?yBaxLay)MnO3 was synthesized using a standard ceramic technique. Rietveld analysis at room temperature indicated that the Mn–O(1) distance increased and the Mn–O(2) distance decreased with the increase in x. The samples were n-type semiconductors and exhibited hopping conductivity in a small-polaron model below 533 K. The Mn3+ ion acted as a donor and the electron transfer became active through the Mn3+–O–Mn4+ path. The samples were antiferromagnetic and the Néel temperature (TN) was constant regardless of y when x was fixed to 0.3, whereas TN shifted to a high temperature when y was fixed to 0.02. The face-sharing Mn3+–O(2)–Mn4+ interaction strengthened as the Mn–O(2) distance decreased, and TN shifted to a high temperature as a result.  相似文献   

17.
The room temperature reaction of (Bu4N)3V5O14 with PhPO3H2 in methanol yields the pentanuclear V(V) cluster (Bu4N)[V5O7(OCH3)2(PhPO3)5]·CH3OH (1·CH3OH). In contrast, the hydrothermal reaction of (Ph4P) [VO2Cl2], PhPO3H2 and (NH4)H2PO4 at 125°C for 96 hr yields the mixed valence V(IV)/V(V) species (Ph4P)2[V5O9(PhPO3)3(PhPO3H)2] (3). While the anions of both 1 and 3 exhibit a pentanuclear core, the structural consequences of 1-electron reduction of the fully oxidized cluster of 1 to produce 3 are quite dramatic, including reduction in coordination numbers at two vanadium sites and protonation of two phosphonate oxygen sites with concomitant structural reorganization. Crystal data: 1, monoclinic P21/n,a=12.167(2) Å,b=23.348(5) Å,c=22.508(5) Å,β=98.49(2)°,V=6323.9(19) Å3,Z=4,D calc=1.558 g cm?3; 3, triclinic, $P\bar 1$ ,a=13.478(3) Å,b=14.399(3) Å,c=23.638(5) Å,α=72.53(2)°,β=85.58(2)°,γ=69.88(4)°,V=4107.0(16) Å3,Z=2, Dcalc=1.479 g cm?3.  相似文献   

18.
《Polyhedron》1986,5(10):1503-1508
The kinetics of the reactions of Ru(II) complexes with CS2N3 ions were studied spectrophotometrically. The formation rate constants data for trans-[Ru(NH3)4L(CS2N3)] are 2.2 × 102, 1.8 × 10 and 1.3 × 102 M−1 s−1 for L = SO2-3, HSO3 and P(OEt)3), respectively [μ = 1.0 M (NaCF3COO), 25°C]. Under the same experimental conditions, the values of k−1 (specific rate for the aquation reaction) are 1.5 × 10−2, 5.0 × 10−2 and 4.5 × 10 s−1 for L = SO2−3, HSO3 and P(OEt)3, respectively. The free-energy change (ΔG) for the systems where L = P(OEt)3 and SO2−3 are in agreement within the experimental error. It was observed that the affinity of the CS2N3 ion decreases with the increasing π-acidity of the auxiliary ligand L. The order of affinity of the CS2N3 ion for the Ru(II) center studies is SO2−3 > HSO3 > P(OEt)3 >SO2.  相似文献   

19.
ABSTRACT

The effects of volume change at dissociation equilibrium of possible anion complexes of the (MX6)3? type in halide melts of trivalent metals MX3 within the statistical thermodynamics based on the MSA approximation were analysed. With the help of a simplified Akdeniz–Tosi model of a mixture of charged hard spheres of different diameters and valencies, we obtained the full system of equilibrium equations including the mass action law (MAL) and the equation of state (EoS). It was shown that the simplest approximation of the complex diameter as a tripled diameter of simple ions leads to a significant overestimation of the effects of volume changes at dissociation. It was found that the complex dissociation should be accompanied by a significant increase in density in a narrow temperature interval. It can be associated with the specific manifestation of electrolytic dissociation in the case of the trivalent metal halides’ auto-complexation.  相似文献   

20.
《Tetrahedron letters》1986,27(6):705-706
Michael addition of two equivalents of methyl vinyl ketone to dimedone, followed by acid-catalyzed cyclization give in 64% overall yield a strained tricyclic molecule with a spiro ring junction.  相似文献   

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