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1.
Density functional GGA-PW91 method with DNP basis set is applied to optimize the geometries of Ag
n
H (n = 1–10) clusters. For the lowest energy geometries of Ag
n
H (n = 1–10) clusters, the hydrogen atom prefers to occupy the two-fold coordination bridge site except the occupation of single-fold
coordination site in AgH cluster. After adsorption of hydrogen atom, most Ag
n
structures are slightly perturbed and only the Ag6 structure in Ag6H cluster is distorted obviously. The Ag–Ag bond is strengthened and the strength of Ag–H bond exhibits a clear odd–even oscillation
like the strength of Au–H bond in Au
n
H clusters, indicating that the hydrogen atom is more favorable to be adsorbed by odd-numbered pure silver clusters. The adsorption
strength of small silver cluster toward H atom is obviously weaker than that of small gold cluster toward H atom due to the
strong scalar relativistic effect in small gold cluster. The pronounced odd–even alternation of the magnetic moments is observed
in Ag
n
H systems, indicating that the Ag
n
H clusters possess tunable magnetic properties by adsorbing hydrogen atom onto odd-numbered or even-numbered small silver
cluster. 相似文献
2.
Structures, binding energies, harmonic frequencies, dipole moments, HOMO–LUMO energy gaps and particularly atoms in molecules
(AIM) analyses of some nanoannular carbon clusters (C4–C20) are investigated at B3LYP/6-31+G(d) level of theory. No correlation is found by plotting the calculated binding energies
as a functional number of carbon atoms of carbon clusters. The calculated binding energies sharply increase from C4 to C10 while slowly from C10 to C20. The binding energies of C4n+2 clusters including C6, C10, C14, and C18 have a clear increase when compared with others indicating their aromatic characters which is confirmed by results of HOMO–LUMO
energy gaps and geometrical parameters. AIM analyses show that most of our carbon clusters are topologically normal (non-conflict)
with stable structures. Nevertheless, the topological networks of small antiaromatic rings, C4 and C8, at their equilibrium geometries may change via molecular vibrations. The existence of straight bond paths in 3D molecular
graphs of carbon clusters with n > 10 implies that ring strains are decreased as the ring sizes grow. Except for C4 and C8, the ellipticity values for the remaining carbon clusters are small indicating that the C–C bond is conserved in these clusters.
Dipole moments of even-numbered structures are negligible, whereas odd-numbered ones have μ values of 0.09−0.73 D. 相似文献
3.
Silmar A. do Monte Elizete Ventura Tamires F. da Costa Sidney R. de Santana 《Structural chemistry》2011,22(3):497-507
Abstract
Ab initio and DFT calculations have been performed to characterize some ground state structures of the title molecules. Relative energies, rotational barriers, NBO charges, and dipole moments (μ) have been calculated and analyzed. It has been confirmed that only highly correlated methods (e.g., CCSD) are able to yield the non-planar structure as a minimum, for the H2NNO molecule. On the other hand, all computational levels here employed are able to yield a planar C2NNO frame for the (CH3)2NNO as a minimum. Important correlations between atomic charges and bond distances are discussed. Replacement of H by methyl group increases the rotational barrier and μ values by at least 3 kcal/mol and 0.4 D, respectively. The largest μ values are obtained for the structures in which the nitrogen lone pair is parallel to the NO group π system, and are consistent with a larger contribution of a dipolar resonance structure. 相似文献4.
The (CH3OH)
n
(n = 2–8) clusters formed via hydrogen bond (H-bonds) interactions have been studied systemically by density functional theory
(DFT). The relevant geometries, energies, and IR characteristics of the intermolecular OH···O H-bonds have been investigated.
The quantum theory of atoms in molecule (QTAIM) and natural bond orbital (NBO) analysis have also been applied to understand
the nature of the hydrogen bonding interactions in clusters. The results show that both the strength of H-bonds and the deformation
are important factors for the stability of (CH3OH)
n
clusters. The weakest H-bond was found in the dimer. The strengths of H-bonds in clusters increase from n = 2 to 8, moreover, the strengths of H-bonds in (CH3OH)
n
(n = 4–8) clusters are remarkably stronger than those in (CH3OH)
n
(n = 2, 3) clusters. The small differences of the strengths of H-bonds among (CH3OH)
n
(n = 6–8) clusters indicate that a partial covalent character is attributed to the H-bonds in these clusters. The linear relationships
between the electron density of BCP (ρb) and the H···O bond length of H-bonds as well as the second-perturbation energies E(2) have also been investigated and used to study the nature of H-bonds, respectively. 相似文献
5.
An all-electron scalar relativistic calculation on Cu
n
H (n = 1–13) clusters has been performed by using density functional theory with the generalized gradient approximation at the
PW91 level. Our results reveal that the hydrogen atom prefers to occupy the two fold coordination site for Cu
n
H (n = 2, 4–6, 8, 10–13) clusters, the single fold coordination site for Cu
n
H (n = 1, 3, 7) and the three fold coordination site for Cu9H cluster. For all Cu
n
H clusters, only the Cu11 structure in Cu11H is distorted obviously. After adsorption, the Cu–Cu bond is strengthened and the Cu–H bond of odd-numbered Cu
n
H clusters is relatively stronger than that of adjacent even-numbered Cu
n
H clusters. The Cu–Cu bond-length and Cu–H bond-length for all Cu
n
H clusters of our work are significantly shorter than those of previous work. This discrepancy can be explained in terms of
the scalar relativistic effect. The most favorable adsorption between small copper clusters and hydrogen atom takes place
in the case that hydrogen atom is adsorbed onto an odd-numbered pure Cu
n
cluster and becomes Cu
n
H cluster with even number of valence electrons. The odd–even alteration of magnetic moments is observed in Cu
n
H clusters and may provide the material with tunable code capacity of “0” and “1” by adsorbing a hydrogen atom onto odd- or
even-numbered copper clusters. 相似文献
6.
Nina I. Giricheva Georgiy V. Girichev Yulia S. Medvedeva Sergey N. Ivanov Anna V. Bardina Vyacheslav M. Petrov 《Structural chemistry》2011,22(2):373-383
A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular
structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four
conformers, two of which are stabilized by intramolecular hydrogen bond. The latter (with the S–N bond in a close to orthogonal
position around the phenyl ring and differing from each other by staggered or eclipsed positions of the N–H and S=O bonds
in the SO2NH2 group) presented in a saturated vapor over 2-NBSA at T = 433 (3) K in commensurable amounts. Experimental internuclear distances (Ǻ) for the staggered conformer are (?): r
h1(C–H)av. = 1.071(9), r
h1(C–C)av. = 1.390(4), r
h1(C–S) = 1.789(8), r
h1(S=O)av. = 1.427(6), r
h1(S–N) = 1.644(6), r
h1(N–O)av. = 1.221(4), r
h1(C′–N) = 1.487(8), r
h1(N–H)av. = 1.014. Calculations at B3LYP/cc-pvtz level were performed to determine the structure and the energies of the transition
states between conformers. It was shown that the conformer structures of free molecule differ from those of a molecule stabilized
by intermolecular hydrogen bonds in a crystal. Influence of a substituent X (X = –CH3, –NO2) on conformational features of the ortho-substituted benzenesulfonamide was established. 相似文献
7.
Abstract
We performed density functional theory calculations for nitrogen-doped models of the representative structures of (6,0) zigzag and (4,4) armchair aluminum phosphide nanotubes (AlPNTs). Our results indicate that the optimized bond distances and tip diameters do not detect the effects of the N-doped regions; however, the effects are observed for the band gap energies and dipole moments. It is noted that substitution of the P atom by the N atom does not influence the value of band gap energy for this N-doped model. The results also indicate that the tendency of the Al atom for contribution to the Al–N bond is stronger than the tendency of the P atom for contribution to the N–P bond; therefore, the latter form of substitution makes the AlPNTs interesting as reactive materials towards other atoms or molecules, especially for the the zigzag AlPNT. 相似文献8.
Abstract
Using ab-initio calculation, we have explored new chemical paths for the coalescence of C60 units into higher fullerenes and novel structures. Besides the Stone–Wales paradigm used for rationalizing the fusion of fullerenes and nanotubes, we demonstrated that an alternative path exists for the fusion of two C60 units. This path uses successive “π–π” additions and subsequent bond reorganizations to lead to a specific C120 peanut-like structure. The energies of the chemical barriers, the intermediate structures, and the final product are markedly lower than their counterparts found in the chemical paths based on Stone–Wales bond rotations. The results rationalize the existence of a temperature range in which peanut-like structures are obtained during thermal treatment of peapod structures. 相似文献9.
The conformational behavior of 1,2-difluoroethane (1), 1,2-dichloroethane (2), 1,2-dibromoethane (3), and 1,2-diiodoethane (4) have been analyzed by means of complete basis set CBS-QB3, hybrid-density functional theory (B3LYP/Def2-TZVPP) based methods
and natural bond orbital (NBO) interpretation. Both methods showed the expected greater stability of the gauche conformation
of compound 1 compared to its anti conformation. Contrary to compound 1, the anti conformations of compounds 2–4 are more stable than their gauche conformation. The stability of the anti conformation compared to the gauche conformation
increases from compound 1 to compound 4. The NBO analysis of donor–acceptor (σ → σ*) interactions showed that the generalized anomeric effect (GAE) is in favor of
the gauche conformation of compound 1. Contrary to compound 1, GAE is in favor of the anti conformations of compounds 2–4. The GAE values calculated (i.e., GAEanti − GAEgauche) increase from compound 1 to compound 4. On the other hand, the calculated dipole moment values for the gauche conformations decrease from compound 1 to compound 4. In the conflict between the GAE and dipole moments, the former succeeded in accounting for the increase of the anti conformation
stability from compound 1 to compound 4. There is a direct correlation between the calculated GAE, ∆[r
c–c(G) − r
c–c(A)] and ∆[r
c–x(A) − r
c–x(G)] parameters. The correlations between the GAE, bond orders, total steric exchange energies (TSEEs), ΔG
Anti–Gauche, ΔG
‡(Gauche → Gauche′, C
2v), ΔG
‡(Anti → Gauche, C
2), dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–4 have been investigated. 相似文献
10.
Abstract
C-2-unsubstituted imidazoline-3-oxides were reduced with NaBH4 in THF to give the corresponding trans-3,5-diarylimidazolidin-1-ols, while under the same conditions C-2-substituted derivatives gave the corresponding ring–chain–ring tautomers. Treatment of the crude reaction mixture from the reduction of C-2-unsubstituted imidazoline-3-oxides with a MeOH–H2O mixture provided reductive C–N bond cleavage to give hydroxylamines, while under the same conditions ring–chain–ring tautomers remained unchanged. 相似文献11.
A systematic density functional theory investigation on C2Au
n
+ (n = 1,3,5) and C2Au
n
(n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like Cs C2Au+ (C=C–Au+) and D∞h C2Au2 (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C2v C2Au3
+ ([Au–C≡C–Au]Au+) and Cs C2HAu2
+([H–C≡C–Au]Au+). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au3) in the head-on coordinated C2v C2Au4 (Au–C≡C–Au3) and the side-on coordinated C2v C2Au5
+ ([Au–C≡C–Au]Au3
+). Similar –Au3 triangular units exist in the head-on coordinated C2v C2HAu3 (H–C≡C–Au3) and D2d C2Au6 (Au3–C≡C–Au3). The existence of stable –Au3 triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au3 triangles originates from the fact that an equilateral D3h Au3
+ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature.
The extension from H/Au analogy to H/Au3 analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials. 相似文献
12.
Abstract
Three Mn(II) coordination polymers based on 1,10-phenanthroline derivatives and mono-, bi-, or trimetallic cores, namely [Mn(L1)(HL1)(Cl)] (1), [Mn(1,4-ndc)(HL1)] (2), and [Mn3(cis-chdc)2(trans-chdc)(L2)2] (3), where HL1 = 1-(1H-imidazo[4,5-f][1, 10]phenanthrolin-2-yl)naphthalen-2-ol, L2 = 2-(4-fluorophenyl)-1H-imidazo[4,5-f][1, 10]phenanthroline, 1,4-ndc = 1,4- naphthalenedicarboxylate and chdc = 1,4-cyclohexanedicarboxylate, have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by physico-chemical and spectroscopic methods. Compound 1 shows a one-dimensional zigzag chain structure. The neighboring chains are extended into a two-dimensional 3-connected (6,3) network by π–π interactions. Interestingly, two (6,3) networks are interpenetrated in a twofold mode. Compound 2 displays a 2D 4-connected (4,4) network structure based on dinuclear Mn(II) units. Adjacent networks are further connected through π–π interactions to form a three-dimensional supramolecular architecture. Compound 3 shows a 2D 4-connected (4,4) network structure based on trinuclear Mn(II) units. Further, the π–π interactions among adjacent networks resulted in a 3D supramolecular architecture for 3. 相似文献13.
Zhi-Wei Zhao Hui-Yan Zhao Jing Wang Qing-Min Ma Ying Liu You-Cheng Li 《Journal of Cluster Science》2012,23(1):133-145
The lowest-energy configurations, electronic structures and magnetic moments of small Lu
n
(n = 2–20) clusters have been investigated within the framework of density functional theory. The results show that Lu
n
(n = 4, 8, 13, and 18) clusters are more stable than their respective neighbors, and structural transformation reveals at n = 16. As the number of atoms increases, the magnetic moments increase in an alternating fashion until they reach a maximum
of 4.00 μB for Lu8 clusters, followed by even–odd oscillation between 0.00 and 1.00 μB over the range n = 9–20. 相似文献
14.
A systematic density functional theory and wave function theory investigation performed in this work reveals a planar-to-icosahedral
structural transition between n = 4–5 in the partially hydrogenated B12H
n
0/− clusters (n = 1–6) upon hydrogenation of all-boron B120/−. Coupled cluster calculations with triple excitations (CCSD(T)) indicate that a distorted icosahedral B12H6 cluster with C2 symmetry is overwhelmingly favored (by 35 kcal/mol) over the recently proposed perfectly planar borozene (D3h B12H6) (Szwacki et al., Nanoscale Res Lett 4:1085, 2009) which proves to be a high-lying local minimum. A similar 2D–3D structural
transition occurs to the corresponding boron boronyl analogues of B12(BO)
n
with n –BO terminals. Detailed adaptive natural density partitioning (AdNDP) analyses reveal the bonding patterns of these quasi-planar
or cage-like clusters which are characterized with delocalized σ and π molecular orbitals. The electron detachment energies
of the concerned anions and excitation energies of the neutrals are also predicted to facilitate their future experimental
characterizations. 相似文献
15.
Anuja P. Rahalkar Sachin D. Yeole Shridhar R. Gadre 《Theoretical chemistry accounts》2012,131(2):1095
Acetylene clusters are prototypical of simple non-aromatic systems bonded through C–H…π interactions. The present work explores
structures and properties of acetylene clusters (C2H2)
n
, n = 8 and 10, employing cluster-building algorithm and molecular tailoring approach (MTA). The former uses electrostatics guidelines
for building (C2H2)8 and (C2H2)10 structures. These clusters are treated at MP2 level of theory with correlation-consistent basis sets using MTA. The Hessian
matrix and vibrational spectra for the best five structures of (C2H2)8 and (C2H2)10 are computed employing MTA. Actual calculations on these clusters using conventional methods employing large basis sets are
prohibitively difficult to perform. All the frequencies for these structures extracted using MTA-based Hessian matrix are
found to be real, confirming their local minimum nature. This study points to the possibility of using the present approach
for exploring structures, energetics and vibrational spectra of even larger clusters at higher levels of theory. 相似文献
16.
Leif Holmlid 《Journal of Cluster Science》2012,23(1):95-114
Ultra-dense deuterium D(−1) can be formed by a catalytic process from Rydberg Matter (RM) of deuterium as reported previously.
Laser-induced inertial confinement fusion (ICF) has recently been observed in this material. The formation of D(−1) is now
studied through experiments observing the deuterium RM clusters D
N
in excitation levels n
B
= 1, 3 and 4. These levels are intermediate in the formation process of D(−1). Laser-induced fragmentation is used, with
neutral time-of-flight (TOF) and TOF–MS measurements of the kinetic energy release (KER) from the quantized Coulomb explosions
(CE). Several types of pure D
N
clusters, mixed clusters containing both D and H atoms, and clusters containing both D and K atoms are identified. The large
planar RM clusters which are common for H and K are less common for D. The neutral D
N
clusters are small and have high kinetic temperature, typically at 100 K instead of 10 K for K
N
and H
N
. Large D
N
+ clusters are only observed when an electric field is applied, probably stabilized by increased cooling. A strong coupling
of the D(1) laser fragmentation signal to the ultra-dense D(−1) signal is observed, and the materials D(1) and D(−1) are two
rapidly interchangeable forms of quantum fluids. 相似文献
17.
Possible geometrical structures and relative stabilities of (F2AlN3)
n
(n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F2AlN3)
n
(n = 2–4) possess cyclic structure containing Al–Nα–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F2AlN3)
n
(n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm−1, and the vibrational modes are N3 asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters
(2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K. 相似文献
18.
G. Pavlović V. Tralić-Kulenović M. Vinković D. Vikić-Topić I. Matanović Z. Popović 《Structural chemistry》2006,17(3):275-285
The supramolecular synthon of amide group in the primary and secondary amides is well recognized to be infinite chains of the C(4) type formed by the intermolecular hydrogen bond of the type N–HO=C. On the other hand, there is a lack of structural data for the thioamides. Three compounds belonging to the class of N-aryl-fura-mides (N-(4-bromophenyl)-5-bromo-2-furancarboxamide, N-(4-chlorophenyl)-5-bromo-2-furancarboxamide) and to the class of N-aryl-thiofuramide (N-(4-methoxyphenyl)-2-furanthiocarboxamide) are prepared and characterized by the NMR spectroscopy in solution; molecular and crystal structures in the solid state have been determined by X-ray single crystal diffractometry and the structures in the gas phase by DFT and AM1 calculations. The investigation is carried out in order to establish supramolecular amide and thioamide synthons of hydrogen bonding patterns in these crystal structures. The geometry of the N–HO=C and the N–HS=C type of hydrogen bonds are compared due to the possibility of the N–H amide group to form intramolecular hydrogen bond with the furan oxygen atom, thus, commonly, leading to the three-center hydrogen bond pattern. The competition between the S=C proton acceptor of thioamides and the other proton acceptors (such as methoxy group) for the amide N–H proton donor group has been investigated. In that context, the above-mentioned compounds are correlated with the others of this class, structurally determined, so far. 相似文献
19.
Helio G. Bonacorso Cleber A. Cechinel Jussara Navarini Rosália Andrighetto Marcos A. P. Martins Nilo Zanatta 《Monatshefte für Chemie / Chemical Monthly》2011,21(6):277-285
Abstract
This work describes the regioselective synthesis of two new series of 1,1′-oxalylbis[3-(alkyl/aryl/heteroaryl)-4,5-dihydro-5-hydroxy-5-(trihalomethyl)-1H-pyrazoles], where the 3-substituents are H, Me, C6H5, 4-FC6H4, 4-ClC6H4, 4-BrC6H4, 4-NO2C6H4, 4,4′-BiPh, and 2-furyl, in a one-pot methodology with ethanol as solvent, from the reaction of 4-alkoxy-4-(alkyl/aryl/heteroaryl)-1,1,1-trihaloalk-3-en-2-ones with oxalyldihydrazide (51–89%). Complementarily, the dehydration reactions of five examples of the described oxalylbispyrazolines are also reported, which furnished the respective 1,1′-oxalylbis[3-(alkyl/aryl/heteroaryl)-5-(trihalomethyl)-1H-pyrazoles] in 53–78% yields without the two C(O)–N bond cleavages. 相似文献20.
Yue Zhu Min Pu De-Cai Fang Yong-Qiang Ji Jing He David G. Evans 《Structural chemistry》2010,21(4):817-825