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1.
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 BH 2+ 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 D4‘h B 4H 46− (cf. C 4H 42−) and D5h B 5H 56− (cf. C 5H 5−), 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. 相似文献
2.
Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As 2(±), As 4(+), GaAs −, GaAs 2(±) and Ga 2As 2(±). This study complements previous theoretical investigations on Ga (±) to Ga 4(±) and GaAs (+). For As 4 tetrahedral symmetry was assumed, and Re of X 1A 1 determined as 4.73 a0. Vertical ionization potentials to several states of As 4+ were calculated. For GaAs 2, GaAs 2+ and GaAs 2−, 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 GaAs 2 is 2B 2 in C 2v. For Ga 2As 2, 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 Ga 2As 2 were studied. The ground states of Ga 2As 2+ and Ga 2As 2− 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 As 2 is higher than that of GaAs, which in turn is higher than that of Ga 2. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga xAs y. 相似文献
3.
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 AlP 4+ and AlP 6+ are predicted to be species with high stabilities and possible to be produced experimentally. 相似文献
4.
Ab initio SCF and CI calculations have been carried out for H n+ and H n− ( n = 3, 5, 7, 9, 11, 13) clusters with a double-zeta plus polarization basis set. The stabilization energy of negative ion clusters H n− is very small (less than 1 kcal) and their existence is critical. The structural difference between positive- and negative-ion clusters are discussed in terms of the bonding ability involved. While H n+ is a charge-transfer complex, the stability of H n− comes mainly from the ion-induced-dipole attractions. The electron correlation effect on the structure and stability of these ion clusters is also discussed. 相似文献
5.
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 (KNO 3) 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−+LHnk→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. 相似文献
6.
High resolution vibration-rotation spectra of 13C 2H 2 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 ν 1 + mν 4 + nν 5, ν 2 + mν 4 + ( n + 2) ν 5 and ν 3 + ( m − 1) ν 4 + ( n + 1) ν 5 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 xij0. 相似文献
7.
Likely candidates for the lowest potential energy minima of (C 60) nCa 2+, (C 60) nF − and (C 60) nI − clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C 60 intermolecular interaction, an averaged Lennard–Jones C 60–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C 60 multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C 60) n cluster, the coordination shell being tetrahedral for Ca 2+ and F −. The I − ion has an octahedral coordination shell in the global minimum for (C 60) 6I −, however for 12 n 8 the preferred coordination geometry is trigonal prismatic. 相似文献
8.
The formation, structure, and reactivity of the nido-11-vertex species B 11H 15, B 11H 14−, B 11H 132−, B 11H 123− and of the closo-12-vertex species B 11H 12−, B 11H 112− are reviewed. The reactivity includes the behavior towards acids, bases, and oxidants as well as cluster expansion reactions, giving closo-11-vertex species of the type EB 11H 11n− or [B 11H 11M] n−. 相似文献
9.
The oxidation state, the mobility and the molecular structure of chromium species present on CrO x–Al 2O 3 catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO 42− species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al 2O 3 surface (species B). The CrO 42− species show high mobility and are probably responsible for the formation of CrO x clusters. 相似文献
10.
Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C 5H 5)Fe(C 5H 4)] can be prepared by oxidation of acylferrocenes FcCOCH 2R or, more efficiently, by oxidation of the isomeric ketones FcCH 2COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH 2PPh 3) +I − via the acylated salts [FcCH(COR)PPh 3] +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/AlCl 3, 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 FcCOCOC 6H 4Ph 3c have been structurally characterised by single-crystal X-ray diffraction. 相似文献
11.
Closo-B nH n−2(CO) 2 ( n = 5–12), isolobal analogues of closo-C 2B n−2H n, have been investigated at the B3LYP/6-311+G **density functional level of theory. The most stable isomers of closo-B nH n−2(CO) 2 are similar to those of closo-C 2B n−2H n in geometric patterns apart from closo-B 6H 4(CO) 2, and closo-B nH n−2(CO) 2 is much less strained than closo-C 2B n−2H n. Energetic analysis identifies closo-B 6H 4(CO) 2, closo-B 12H 10(CO) 2 and closo-B 10H 8(CO) 2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B nH n−2(CO) 2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed. 相似文献
12.
Structure, electronic state and energy of Si nC − and Si nC −2 ( n=1–7) anions have been investigated using the density functional theory. Structural optimization and frequency analysis are performed at the level B3LYP/6-311G(d). The charged-induced structural changes in these anions have been discussed. The strong C–C bond is also favored over C–Si bonds in the Si nC −m anions in comparison with corresponding neutral cluster. Among different Si nC − and Si nC −2 ( n=1–7) anions, Si 3C −, Si 5C − and Si 2C −2 are most stable. Their stability has a decreasing tendency with the increase in the size of these clusters. 相似文献
13.
The phophorescence of biacetyl induced by an energy transfer to biacetyl from triplet benzene produced in the pulse radiolysis of benzene-biacetyl mixtures has been studied. The time required to reach the maximum intensity of phosphorescence, tmax, after the electron pulse, varies as a function of biacetyl pressure at constant benzene pressure (40 torr), which gives the lifetime of triplet benzene τ = (6.7 ± 3.2) × 10 −6 s and the rate constant of the energy transfer kC6H6*(T1) + biacetyl = (1.6 ± 0.7) × 10 −10 cm 3 molecule −1 s −1. 相似文献
14.
Nickel(II) chromate complex with imidazole (HIm) was isolated from the [Ni 2+–HIm–CrO 42−] system in various experimental conditions, i.e. reagent molar ratios and nickel(II) salts. The catena( μ-CrO 4- O, O′)[Ni(HIm) 3H 2O] (1) crystallizes in monoclinic crystal system—space group P2 1/ n with cell parameters: a=11.784(2), b=8.899(2), c=13.934(3) (Å), β=95.19(3) (°). The unit cell contains two independent helixes, left- and right-handed, stabilized by intrahelical and interhelical hydrogen bonds (HB) and π–π interactions. The cis coordination of the CrO 42− anions and the HB systems appeared to be the main determinants of the helical architecture. To the best of our knowledge the cis-chromate coordination was observed for the first time. The cis coordination causes the distortion of the nickel octahedron, which was analysed by 4 K single crystal electronic spectra with D4h symmetry approximation (gaussian resolution and crystal field parameters). This symmetry was also confirmed with the polarised electronic spectra. The magnetic properties of the complex suggest the occurrence of weak intrachain antiferromagnetic interactions between the magnetic Ni II center. The computational DFT studies of complex 1 assuming three possible isomers mer[(HIm) 3]– cis[(CrO 42−) 2], mer– trans and fac– cis suggested that the main contribution to the stability of 1 might have interhelical and intrahelical hydrogen bonds. 相似文献
15.
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 C3V and the D3h point group as well as for n=4 in the Td (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface. 相似文献
16.
Mg +—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X 2Σ + → 2Π is observed with an origin at 31387 cm −1 (vac) for 24Mg +—Ar. The 24Mg +—Ar spectrum is characterized by a 15 member progression with a frequency (ω′ e) of 272 cm −1. An extrapolation of this progression fixes the excited state dissociation energy ( D′ o) at 5552 cm −1. The corresponding ground-state value ( D″ o) is 1270 cm −1 (3.6 kcal/mol). The 2Π
,
spin—orbit splitting is 76 cm −. 相似文献
17.
Geometries and vibrational frequencies of complexes of cationic coinage metal clusters M n+ (M=Cu, Ag, Au; n=1–4) and H 2S are computed using density functional theory. Thermochemical values for M n+H 2S decomposition channels involving loss of an H atom, H 2 molecule, M atom, or M 2 molecule are also computed. Significantly different results are obtained for closed-shell ( n odd) and open-shell ( n even) complexes. 相似文献
18.
Twenty-two isomers/conformers of C 3H 6S +√ radical cations have been identified and their heats of formation (Δ Hf) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their Δ Hf data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation (4 +) with C2v symmetry. In contrast, the least energy C 3H 6O +√ isomer is the 1-propen-2-ol radical cation. The G3 Δ Hf298 of 4 + is calculated to be 859.4 kJ mol −1, ca. 38 kJ mol −1 higher than the literature value, ≤821 kJ mol −1. For allyl mercaptan radical cation (7 +), the G3 Δ Hf298 is calculated to be 927.8 kJ mol −1, also not in good agreement with the experimental estimate, 956 kJ mol −1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 Δ Hf298 values for 4 + and 7 + should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent. Cation CH3CHSCH2+√ (10+) has the least energy among the eleven distonic radical cations identified. Their ΔHf298 values range from 918 to 1151 kJ mol−1. Nevertheless, only one of them, CH2=SCH2CH2+√ (12+), has been observed. Its G3 ΔHf298 value is 980.9 kJ mol−1, in fair agreement with the experimental result, 990 kJ mol−1. A couple of reactions involving C3H6S+√ isomers CH2=SCH2CH2+√ (12+) and trimethylene sulfide radical cation (13+) have also been studied with the G3 method and the results are consistent with experimental findings. 相似文献
20.
近年来,对金属簇的研究已成为化学与物理学中最活跃的研究领域之一[1].金属簇被认为是介于单个原子与固体之间的中间相[2].深入地研究其结构、形成机理及物理与化学行为,对于寻找新的催化剂[3],重新认识气相化学与凝聚相化学的关系[4],都有非常重要的意... 相似文献
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