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1.
Using the first-principle density functional calculations, the equilibrium geometries and electronic properties of anionic and neutral aluminum-sulfur Al n S m (2?≤?n?+?m?≤?6) clusters have been systematically investigated at B3PW91 level. The optimized results indicate that the lowest-energy structures of the anionic and neutral Al n S m clusters prefer the low spin multiplicities (singlet or doublet) except the Al2 ̄, Al2, S2, Al4 and Al2S4 clusters. A significant odd-even oscillation of the highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps for the Al n S m  ̄ clusters is observed. Electron detachment energies (both vertical and adiabatic) are discussed and compared with the photoelectron spectra observations. Furthermore, a good agreement between experimental and theoretical results gives confidence in the most stable clusters considered in the present study and validates the chosen computational method. In addition, the variation trend of chemical hardness is in keeping with that of HOMO-LUMO energy gaps for the Al n S m clusters. Upon the interaction of oxygen with the stable AlS m  ̄ clusters, the dissociative chemisorptions are favorable in energy. The binding energy and Gibbs free energy change show completely opposite oscillating behaviors as the cluster size increases.  相似文献   

2.
The possibility of a new endohedral fullerene with a trapped aluminum carbide cluster, Al4C @C80-I h , was theoretical investigated. The geometries and electronic properties of it were investigated using density functional theory methods. The Al4C unit formally transfers six electrons to the C80 cage which induces stabilization of Al4C@C80. A favorable binding energy, relatively large HOMO-LUMO gap, electron affinities and ionization potentials suggested the Al4C@C80 is rather stable. The analysis of vertical ionization potential and vertical electron affinity indicate Al4C@C80 is a good electron acceptor.
Figure
An endohedral fullerene with a trapped aluminum carbide cluster, Al4C @C80-I h , was investigated using density functional theory. A favorable binding energy, relatively large HOMO-LUMO gap, electron affinities and ionization potentials suggested it is rather stable  相似文献   

3.
The neutral PrSi n (n = 12–21) species considering various spin configurations were systematically studied using PBE0 and B3LYP schemes in combination with relativistic small-core potentials (ECP28MWB) for Pr atoms and cc-pVTZ basis set for Si atoms. The total energy, growth-pattern, equilibrium geometry, relative stability, hardness, charge transfer, and magnetic moments are calculated and discussed. The results reveal that when n < 20, the ground-state structure of PrSi n evaluated to be prolate clusters. Starting from n = 20, the ground-state structures of PrSi n are evaluated to be endohedral cagelike clusters. Although the relative stabilities based on various binding energies and different functional is different from each other, the consensus is that the PrSi13, PrSi16, PrSi18, and PrSi20 are more stable than the others, especially the PrSi20. Analyses of hardness show that introducing Pr into Si n (n = 12–21) elevates the photochemical sensitivity, especially for PrSi20. Calculated result of magnetic moment and charge transfer shows that the 4f electrons of Pr in the clusters are changed, especially in endohedral structures such as PrSi20, in which one electron transfers from 4f to 5d orbital. That is, the 4f electron of Pr in the clusters participates in bonding. The way to participate in bonding is that a 4f electron transfers to 5d orbital. Although the 4f electron of Pr atom participates in bonding, the total magnetic moment of PrSi n is equal to that of isolated Pr atom. The charge always transfers from Pr atom to Si n cluster for the ground state structures of PrSin (n = 12–19), but charge transfer is reverse for n ≥ 20. The largest charge transfer for endohedral structure reveals that the bonding between Pr and Si n is ionic in nature and very strong. The fullerenelike structure of PrSi20 is the most stable among all of these clusters and can act as the building blocks for novel functional nanotubes.  相似文献   

4.
The structures and stabilities of As2-doped Sin (n = 1-7) clusters have been investigated at the B3LYP level of theory, incorporating the 6-311+G basis set. An isosceles triangle is predicted to be the lowest-energy structure of the As2Si cluster, whereas the global minimum of As2Si2 possesses an As-As-butterfly structure. The ground state structures for As2Si3, As2Si4 and As2Si5 are all bipyramids: trigonal, tetragonal and pentagonal, respectively, which could have important applications as building blocks to synthesize silicon nanowires. The most stable isomer of As2Si6 possesses a tricapped trigonal bipyramid structure. The lowest energy structure of As2Si7 can be viewed as a substitutional structure of the tricapped trigonal prism Si9 isomer. In the majority of the lowest energy isomers, the two As atoms tend to be separated from each other, in order to maximize the number of Si-As bonds, and therefore locate at the axial vertex or face-capping atomic positions, especially for As2Si4-As2Si7. According to results of the incremental binding energies, the HOMO-LUMO gaps and the vertical ionization potentials, the As2Si3 and As2Si6 clusters are relatively stable compared to their neighbors. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds play an important role in stabilizing the low-energy As2Sin structures.  相似文献   

5.
The total energies, growth patterns, equilibrium geometries, relative stabilities, hardnesses, intramolecular charge transfer, and magnetic moments of HoSi n (n?=?12–20) clusters have been reexamined theoretically using two different density functional schemes in combination with relativistic small-core Stuttgart effective core potentials (ECP28MWB) for the Ho atoms. The results show that when n?=?12–15, the most stable structures are predicted to be exohedral frameworks with a quartet ground state, but when n?=?16–20, they are predicted to be endohedral frameworks with a sextuplet ground state. These trend in stability across the clusters (gauged from their dissociation energies) was found to be approximately the same regardless of the DFT scheme used in the calculations, with HoSi13, HoSi16, HoSi18, and HoSi20 calculated to be more stable than the other clusters. The results obtained for cluster hardness indicated that doping the Ho atom into Si13 and Si16 leads to the most stable HoSi n clusters, while doping Ho into the other Si n clusters increases the photochemical sensitivity of the cluster. Analyses of intracluster charge transfer and magnetic moments revealed that charge always shifts from the Ho atom to the Si n cluster during the creation of exohedral HoSi n (n?=?12–15) structures. However, the direction of charge transfer is reversed during the creation of endohedral HoSi n (n?=?16–20) structures, which implies that Ho acts as an electron acceptor when it is encapsulated in the Si n cage. Furthermore, when the most stable exohedral HoSi n (n?=?12–15) structures are generated, the 4f electrons of Ho are virtually unchanged and barely participate in intracluster bonding. However, in the most stable endohedral HoSi n (n?=?16–20) frameworks, a 4f electron does participate in bonding. It does this by transferring to the 5d orbital, which hybridizes with the 6s and 6p orbitals and then interacts with Si valence sp orbitals. Meanwhile, the total magnetic moments of the HoSi n (n?=?16–20) clusters are considerably higher than those of HoSi n (n?=?12–15). Interestingly, the endohedral HoSi16 and HoSi20 clusters can be viewed as the most suitable building blocks for novel high-density magnetic storage nanomaterials and for novel optical and optoelectronic photosensitive nanomaterials, respectively.  相似文献   

6.
The equilibrium geometries and electron affinities of the R-SS/R-SS-(R=CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, t-C4H9, n-C5H11) species have been studied using the higher level of the Gaussian-3(G3) theory and 21 carefully calibrated pure and hybrid density functionals (five generalized gradient approximation (GGA) methods, seven hybrid GGAs, three meta GGA methods, and six hybrid meta GGAs) in conjunction with diffuse function augmented double-ζ plus polarization (DZP++) basis sets. The geometries are fully optimized with each method and discussed. The reliable adiabatic electron affinity has been presented by means of the high level of G3 technique. With the DZP++ DFT method, three measures of neutral/anion energy differences reported in this work are the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy. The adiabatic electron affinities, obtained at the BP86, M05-2X, B3LYP, M06, B98, M06-2X, mPW1PW91, HCTH, B97-1, M05, PBE1PBE, and VSXC methods, are in agreement with the G3 results. These methods perform better for EA prediction and are considered to be reliable.  相似文献   

7.
The structures, stabilities, and aromaticities of a series of (BCO) n (CH)4–n NH (n?=?0–4), (BCO) n (CH)4–n O (n?=?0–4), and (BCO) n (CH)4–n S (n?=?0–4) clusters were investigated at the B3LYP density functional level of theory. The most stable positional isomers of the individual clusters were obtained. All of the calculated CO binding energies were exothermic, suggesting that these BCO-substituted species are stable. Calculated differences in strain energy between the BCO-substituted structures and their corresponding hydrocarbon clusters were all exothermic, indicating that the BCO-substituted structures are less strained. The negative nucleus-independent chemical shift (NICS) values obtained show that these BCO-substituted clusters are aromatic compounds, in good agreement with the aromaticities of the corresponding hydrocarbon species. To aid further experimental investigations, CO-stretching frequencies were also computed.  相似文献   

8.
A series of novel asymmetric binuclear titanocenes linked with alkyl benzyl ethers p-[(C5H5TiCl2)C5H4CH2]C6H4O(CH2)n[C5H4(TiCl2C5H5)] (n = 2-5) (13-16) have been synthesized by treating p-(LiC5H4CH2)C6H4O(CH2)n(C5H4Li) (n = 2-5) (9-12) with C5H5TiCl3. The new complexes have been characterized by elemental analysis and NMR spectra. Their catalytic activity for ethylene polymerization was investigated in the presence of aluminoxane (MAO). The results show that 13-16 are efficient catalysts for producing polyethylene (PE) with a broad molecular weight distribution (MWD). Their catalytic activity is highly dependent on the length of the alkyl chain and the polymerization conditions. A longer alkyl chain increases the catalytic activity, whereas the molecular weight of the produced polyethylene decreases.  相似文献   

9.
Ab initio methods based on density functional theory at BP86 level were applied to the study of the geometrical structures, relative stabilities, and electronic properties of small bimetallic Be2Au n (n = 1–9) clusters. The optimized geometries reveal that the most stable isomers have 3D structures at n = 3, 5, 7, 8, and 9. Here, the relative stabilities were investigated in terms of the averaged atomic binding energies, fragmentation energies and second-order difference of energies. The results show that the planar Be2Au4 structure is the most stable structure for Be2Au n clusters. The HOMO−LUMO gap, vertical ionization potential, vertical electron affinity and chemical hardness exhibit a pronounced even–odd alternating phenomenon. In addition, charge transfer and natural electron configuration were analyzed and compared.  相似文献   

10.
The properties of noble gas systems can be greatly extended by heterogeneous mixtures of elements. The geometrical structures and energies of mixed Ar–Kr–Xe clusters were investigated using ternary Lennard-Jones (TLJ) potential. For the Ar19Kr n Xe19, Ar19Kr19Xe n , and Ar n Kr19Xe19 (n?=?0–17) clusters investigated, the results show that only two minimum energy configurations exist, i.e., polytetrahedron and six-fold pancake. The inner core of all these clusters is composed mainly of Ar atoms, and Kr and Xe atoms are distributed on the surface with well mixed pattern for polytetrahedral and segregate pattern for six-fold pancake configurations. The relative stability property of Ar–Kr–Xe clusters with a certain composition is discussed. Moreover, the role of heterogeneity on the strain was investigated, and reduced strain energies in Ar–Kr–Xe clusters were studied to find possible ways of reducing strain. The results showed that the strain energies were affected mainly by Ar–Ar, Ar–Kr, and Xe–Xe bonds.
Figure
Investigation of the structures of Ar19Kr n Xe19, Ar19Kr19Xe n , and Ar n Kr19Xe19 (n?=?0–17) clusters reveal the existence of only exist two minimum energy configurations, i.e., polytetrahedron and six-fold pancake. Furthermore, reduced strain energies in Ar–Kr–Xe clusters were studied for the possible ways of reducing strain.  相似文献   

11.
The new chiral and functionalized cyclic binaphthoxyphosphazenes R,R,R-[N3P3(O2C20H10Br2)3] (R-1), R,R,R-[N3P3(O2C20H10(CCSiMe3)2)3] (R-2), and the high molecular weight linear polymers R/S-[NP(O2C20H10Br2)]n (R/S-3), R-[NP(O2C20H10Br2)]n (R-3), and R-{NP[O2C20H10(CCSiMe3)2]}n, (R-4), with Mw on the order of 106 and very high Tg, have been synthesized and characterized by IR and NMR spectroscopy. The optically active polymer (R-3) was configurationally stable below 300 °C, but at higher temperatures an atropisomerization process took place that became faster near the glass transition temperature (ca. 350 °C).  相似文献   

12.
Material from the testa of decorticated barley grains contained hydrocarbons, esters, triglycerides, free sterols, 5-n-alkylresorcinols, and traces of free alcohols, carbonyl compounds, and various polar, acidic materials. The hydrocarbon fraction was mainly a series of n-alkanes, extending at least from C11 to C36, in which the C29 and C31 components were prominent. Two minor series of alkanes were also present. Sometimes a trace of an unsaturated hydrocarbon was detected. The ester fraction contained sterols and alkanols esterified by fatty acids, which differed in relative amounts from the fatty acids found in the triglycerides. The triglycerides were thought to have leached from within the grain. At least five free sterols were present, including sitosterol and campesterol. The 5-n-alkylresorcinols were at least twelve members of a homologous series, of which four, C25, C27, C29, and C31, made 98% of the total. Members of the series with even numbers of carbon atoms were also present. It is suggested that they are partly responsible for excluding microorganisms from the interior of the grain. The testa membrane, with the associated pigment strand, contained an estolide of fatty acids and various hydroxyacids, a polysaccharide component, and uncharacterized material.  相似文献   

13.
14.
The geometries, stabilities, and electronic properties of ScBn (n?=?1–12) clusters have been systematically investigated by using density functional theory B3LYP method and coupled–cluster theory CCSD(T) method. It is found that the ground state isomers of ScBn have planar or quasi–planar structure when n?≤?6, which can be viewed as a B atom of the corresponding Bn+1 cluster is substituted by a Sc atom. From n?≥?7, the ground state isomers favor nest–like structure, in which the Sc atom sits on a nest–like Bn cluster. The calculated second–order differences of energies manifest that the magic numbers of stability are n?=?3, 7, 8, 9 and 11 for the ScB n clusters. Further analysis indicates that the ScB7 cluster with C 6v symmetry represents the outstanding stable ScBn cluster, as confirmed by its electronic structure and molecular orbitals.  相似文献   

15.
Three new 2D PbII coordination polymers containing 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethane (bpa) and 1,2-bis(4-pyridyl)ethene (bpe) with bromide anions, [Pb(μ-4,4′-bipy)(μ-Br)2]n (1), [Pb(μ-bpa)(μ-Br)2]n (2) and [Pb(μ-bpe)(μ-Br)2]n (3) have been synthesized and characterized by elemental analysis, IR spectroscopy and their structures studied by X-ray crystallography. The thermal stability of compounds 1-3 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single-crystal X-ray data shows that the Pb2+-ions have coordination numbers of six and contain the rarely holodirected geometries.  相似文献   

16.
Oxylipin glucosides (2-4) were isolated from Lemna paucicostata with their structures and absolute configurations elucidated by spectroscopic and chemical methods. Compounds 2-4 were glucosides of C14 oxylipin which were synthesized from α-linolenic acid via the 9-lipoxygenase pathway.  相似文献   

17.
Nine branched hydrocarbons of the botryococcene type (CnH2n-10 30 ? n ? 37) have been isolated from the green alga Botryococcus braunii. Hydrocarbon mixtures were recovered from wild algae collected in fresh water lakes or from the same strains growing in laboratory; they were further separated by reversed-phase, and in some cases by normal phase, HPLC. From chemical investigations, GC/MS analyses, 1H and 13C NMR spectroscopy, the structures of four new botryococcenes (one C33H56, two C34H58 and one C37H64) were elucidated.  相似文献   

18.
Calculations performed at the ab initio level using the recently reported planar concentric π-aromatic B18H6 2+(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B3n H m polycyclic aromatic hydroboron (PAHB) clusters—B30H8(2), B39H9 2?(3), B42H10(4/5), B48H10(6), and B72H12(7)—which appear to be the inorganic analogs of the corresponding C n H m polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C10H8, phenalenyl anion C13H9 ?, phenanthrene/anthracene C14H10, pyrene C16H10, and coronene C24H12, respectively, in a universal atomic ratio of B:C?=?3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B20, and experimental syntheses of these snub B3n H m clusters through partial hydrogenation of the corresponding bare B3n may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry.
Figure
Ab initio calculations predict the existence of polycyclic aromatic hydroboron clusters as fragments of a boron snub sheet; these clusters are analogs of polycyclic aromatic hydrocarbons  相似文献   

19.
To assign the observed vibrationsl modes in the resonance Raman spectrum of the retinylidene chromophore of rhodopsin, we have studied chemically modified retinals. The series of analogs investigated are the n-butyl retinals substituted at C9 and C13. The results obtained for the 11-cis isomer have clearly assigned the CCH3 vibrational frequencies observed in the spectrum of the retinylidene chromophore. The data show that the C(9)CH3 stretching vibration can be assigned to the vibrational mode observed in the 1017 cm?1 region, and the vibration detected at 997 cm?1 can be assigned to the C(13CH3 vibration. The C(5)CH3 stretching mode does not contribute to the vibrations observed in this region. The splitting in the C(n)CH3 (n = 9, 13) vibration is characteristic of the 11-cis conformation. The results on the modified retinals do not support the hypothesis that the splitting arises from equilibrium mixtures of 11-cis, 12-s-cis and 11-cis, 12-s-trans in solution. Thus, this splitting cannot be used to determine whether the chromophore in rhodopsin is in a 12-s-cis or 12-s-trans conformation. However, our results demonstrate that there are other vibrational modes in the spectra which are sensitive to this conformational equilibrium and we use the presence of a strong ~ 1271 cm?1 mode in bovine and squid rhodopsin spectra as an indication that the chromophore in these pigments is 11-cis, 12-s-trans.  相似文献   

20.
We perform a systematical investigation on the geometry, thermodynamic/kinetic stability, and bonding nature of low-lying isomers of BnPt (n=1-6) at the CCSD(T)/[6-311+G(d)/LanL2DZ]//B3LYP/[6-311+G(d)/LanL2DZ] level. The most stable isomers of BnPt (n=1-6) adopt planar or quasi-planar structure. BnPt (n=2-5) clusters can be generated by capping a Pt atom on the B-B edge of pure boron clusters. However, For B6Pt with non-planar structure, a single doped Pt atom significantly affects the shape of the host boron cluster. The dopant of the Pt atom can improve the stability of pure boron clusters. The valence molecular orbital (VMO), electron localization function (ELF), and Mayer bond order (MBO) are applied to gain insight into the bonding nature of BnPt (n=2-6) isomers. The aromaticity for some isomers of BnPt (n=2-6) is analyzed and discussed in terms of VMO, ELF, adaptive natural density partitioning (AdNDP), and nucleus-independent chemical shift (NICS) analyses. Results obtained from the energy and cluster decomposition analyses demonstrate that B2Pt and B4Pt exhibits as highly stable. Importantly, some isomers of BnPt (n=2-5) are stable both thermodynamically and kinetically, which are observable in future experiment.  相似文献   

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