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1.
V. V. Pinyaskin E. G. Gal'pern I. V. Stankevich A. L. Chistyakov 《Russian Chemical Bulletin》1997,46(1):49-51
Simulations of the geometric and electronic structure of C44, C45, Si45, C40Si5, and C44Si clusters were performed by the MNDO method. The geometries of the filled clusters, calculated by the MM2 method, were used
as initial approximations. It was found that the filled clusters C45 and C44Si are transformed into endohedral clusters X@C44 (X-C or Si, respectively) after energy optimization. The highest occupied energy level of the HOMO of the filled tetrahedral
cluster Si45 ofT symmetry is triply degenerate and is only occupied by four electrons. The structure of Si45
2− dianion ofT symmetry was calculated. Two filled structures for the C40Si5 cluster were found. The coordination numbers of the central Si atom in these structures are 4 and 3, respectively.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 54–56, January, 1997. 相似文献
2.
V. P. Meleshko 《Journal of Structural Chemistry》1999,40(1):16-22
The structures of Sin and SinHn fullerenes with 20 ≶n ≶60 are calculated in the MINDO/3 approximation using the Monte Carlo technique for geometry optimization.
The calculations show that spheroidal silicon clusters consisting of more than 36 atoms are stable and the bond energy increases
with their size. This increase is not noticed for compact clusters calculated as an alternative. For n ≥40-50, the latter
have lower bond energies compared to fullerenes. The geometry optimization of the tetrahedral cluster Si45 results in a structure close to spheroidal, which gains in bond energy. The addition of hydrogen atoms to small deformed
fullerenes and their geometry optimization make it possible to obtain stable spheroidal structures SinHn whose bond energy is greater than that of alternative compact silicon hydride clusters. When the size of spheroidal clusters
SinHn increases, i. e., when n > 36, the hydrogen elimination barriers decrease abruptly; the SinHn diamond structure of the cluster is more advantageous when n ≥50. 相似文献
3.
The pseudo element concept is applied to isolated Zintl anions [Y10M]n—, where M is Ni or Zn, and Y is a third group element, which is replaced by a fourth group element X. The aim of the theoretical study is to identify stable binary metal atom clusters and to test the robustness of the Zintl concept. DFT and RIMP2 methods are employed for this purpose. All low‐energy isomers of [X10M]m+ show structures known from corresponding Zintl anions. A partial replacement of only six third group elements, however, may lead to different low‐energy topologies. The cohesive energy of the clusters X10Ni (X = Si, Ge, Sn, Pb) is significantly higher than that of the bare X10 species, binding energy of the Ni atom amounts to about 5 eV. 相似文献
4.
Zagumennov V. A. Vedernikov A. N. Nikitin E. V. Solomonov B. N. 《Russian Journal of General Chemistry》2003,73(6):921-927
For a series of diphosphonium salts containing two positively charged covalently bonded phosphorus atoms, X/sub>
n
Y3-n
P+P+X
n
Y3-n
(X = alkyl substituent, Y = amino group, n = 0-3), the stability, reactivity, and P-P bond strength were evaluated by various physicochemical methods. The P-P bond energy is appreciably influenced by both steric factors and donor properties of the substituents. The calculations confirmed that transformations of diphosphonium salts can involve cleavage of both P-P and P-N (or P-C) bonds. 相似文献
5.
É. N. Yurchenko 《Journal of Structural Chemistry》1996,37(2):217-223
The paper describes methods for determining the force fields of large sets of molecules which share the common property that
in their constituent groups of molecules the equivalent force constants always change monotonically with the properties of
substituent atoms belonging to the same subgroup of the periodic table. The force fields of the CH4−nXn (n=0–4, X=F, Cl, Br, I) molecules of the methane series are obtained. The applications of these force fields are discussed.
In particular, they can serve as a basis for a data bank of the force fields of fragments suitable for constructing the force
fields of more complex molecules.
Russian Scientific Center “Applied Chemistry”, St. Petersburg. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 250–256, March–April, 1996.
Translated by I. Izvekova 相似文献
6.
V. S. Gurin 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,42(1):65-70
Semiempirical (by extended Hückel method) and ab initio RHF SCF calculations are used for the wide range of cluster structures MxXy, where M = Cd,Ag; X = S,I: semiempirical - up to M20X35, and ab initio - for small clusters less than ten atoms. Variation of electronic structure with size for the fragments with tetrahedral coordination (bulklike sphalerite structures) and for some clusters of the lower symmetry allows to predict their possible geometries which are compared with experimental data. The chemical bonding factor (the chemical nature of bounded atoms, coordination number for metal and non-metal atoms, hybridization, etc) is of more importance in properties of the clusters than the familiar quantum confinement effect of semiconductor clusters (like CdS, CdSe, PbS, etc. ). The essential difference in regularities of small cluster formation is analysed for CdS- and AgI- based structures. 相似文献
7.
G. S. Anagnostatos 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):125-127
Small clusters made up of three kinds of neutral alkali atoms, i.e. clusters of the form X ? Y m Z n , are theoretically studied. These clusters exhibit three series of magic numbers, one for each kind of atoms. That is,?,m, andn independently can be magic numbers rather than their cumulative number?+m+n or, in other words, magic numbers in alkali clusters composed of neutral atoms are due to atoms rather than to delocalized electrons as in jellium model. Of course, if conditions favor delocalization of electrons,?+m+n can be magic but then we have no neutral atoms which are prerequisite for an application of the present model. 相似文献
8.
In the M-T-O model system (M is a polyvalent metal with CN ≥ 4; T is Si), cyclic clusters have been deduced as graphs in the
T/M range from one to three. The case is considered when monocyclic cluster M2T2 is modified by T-tetrahedra that form diortho groups T2. The M sites of the cluster have either topologically different local MT structures (four types) or identical local MT structures
(two types). The cluster types for T/M = 3 obtained by modeling were used in analysis of one of the most complicated types
of silicate crystal structures Na3MSi3O9 (M = Y; Eu-Lu; T/M = 3) with the Pearson index oP256 and 64 independent atoms. The TOPOS program package was used to carry
out the complete 3D reconstruction of the self-assembly of the crystal structure: suprapolyhedral precursor nanocluster →
primary chain → microlayer → microframework (supraprecursor) → ... three-dimensional framework. The calculation of the coordination
sequences of site atoms in the 3D network of the MT framework MT3O9 revealed topological symmetry related to a three-dimensional separation of the framework into two interpenetrating frameworks.
Each framework structure is generated by topologically equivalent cyclic precursor clusters Na2M2T6 consisting of two YO6 octahedra comprising three diortho groups Si2O7 and two Na atoms located above and below the ring center. The 3D graphs characterizing the connectivity of the centers of
crystallographically equivalent clusters in the frameworks correspond to diamond-type networks. 相似文献
9.
E. T. Denisov 《Russian Chemical Bulletin》2005,54(4):914-923
Interatomic distances in the reaction centers of the addition reactions of (i) H· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ·CH3 radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined
using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the
type X· + Y=Z → X— Y—Z· the r
#
X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined
for seventeen classes of radical addition reactions. The bond elongation, Δr
#
X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the
reaction center, and the force constant of the attacked multiple bond increase.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005. 相似文献
10.
Ternary Compounds of Lithium with Yttrium, Lanthanum, or Neodymium and Elements of the Fifth Main Group in a “Filled” CaAl2Si2-type Structure Formation and crystal structure of ternary compounds with lithium and yttrium, lanthanum or neodymium and elements of the fifth main group of the composition ALi3X2v (A = Y, La, Nd; Xv = P, As, Sb, Bi) are reported. Crystal structure determination by X-ray and neutron diffraction methods show that the compounds crystallize in a ?filled”? CaAl2Si2 structure. Two Li atoms of the formula occupy the Al sites in distorted tetrahedral Xv holes of the lattice, the slightly distorted octahedral holes of the Xv atoms are filled with A and the third Li atom. 相似文献
11.
R. M. Minyaev 《Journal of Structural Chemistry》1996,37(5):713-721
An ab initio (STO-3G basis set) method is used to calculate the pathways and activation barriers of cooperative biproton migrations
in the associates of the formic acid molecule with water and YH (YH=H2O, HOF, and HOOH). The associate with YH=H2O exhibits a cooperative triproton transfer with an activation barrier of 4.46 (Cs symmetry) or 3.08 kcal/mole (C2 symmetry); in the systems with Y=HOF and HOOH, the biproton transfer is accompanied by synchronous shifts of two hydroxyl
groups and has the activation barriers of 75.03 (C2, Y=HOF), 75.74 (Cs, Y=HOF), and 89.62 kcal/mole (Y=HOOH). The hypothesis of stereochemical similarity for low-barrier cooperative processes
in molecular associates is proposed.
Scientific Research Institute of Physical and Organic Chemistry, Rostov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 834–844, September–October, 1996.
Translated by I. Izvekova 相似文献
12.
Based on the results of NMR studies of series of polyene compounds Ph(CH=CH)nCH=CXY (X, Y are acceptor substituents), it is suggested that the ratio of vicinal spin-spin coupling constants of protons
at the neighboring CH=CH and CH-CH bonds of the same chain be used as a criterion for the degree of charge transfer (equalization
of bonds). Conditions (n, X, Y) have been determined under which the ratio is minimal.
Institute of Nutrition Substances, Russian Academy of Sciences. Translated fromZhumal Struktumoi Khimii, Vol. 36, No. 4, pp. 703–708, July–August, 1995.
Translated by L. Smolina 相似文献
13.
S. Saito S. Ohnishi C. Satoko S. Sugano 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,14(3):237-245
We propose the “triangle contraction” as an important reconstruction mechanism of six-membered-ring silicon clusters on the basis of the force and virial analysis for Si6, Si10, Si14, Si18, Si22, and Si26 clusters. Forces acting on atoms have been calculated using the local-density-functional scheme with linear-combination-of-atomic-orbitals-Xα method. Calculated forces show that most of the (111)-surface equilateral triangles have tendency to contract, indicating the generality of the triangle-contraction mechanism. 相似文献
14.
A. I. Pavlyuchko 《Journal of Structural Chemistry》1997,38(6):959-964
A universal program for variational calculations of molecular symmetry in solving anharmonic vibrational problems, realized
by the author, is described. The program uses the group-theoretical method. Symmetrized basis wave functions are constructed
with the aid of the generalized KJebsch-Gordan series suggested by the author. The method of constructing symmetrized basis
wave functions and the program for adequate calculations of molecular symmetry were verified for many molecules of different
symmetry groups: Oh, O, Td, Th, T, D∞h, Ct8v, Dnd, Dnh, Dn, Cnv, Cnh, S2n, Cn, Ci, Cs, and C1 where 2 ≤n ≤6. It was confirmed that the program provides correct results and high-speed operation.
Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1146–1153, November–December, 1997. 相似文献
15.
Donald C. Dittmer Bhalchandra H. Patwardhan John T. Bartholomew 《Magnetic resonance in chemistry : MRC》1982,18(2):82-86
Carbon-13 chemical shifts of the α- and β-carbon atoms for 12 thietane 1,1-dixides, 9 thietane 1-oxides and 7 thietanes with a variety of 3-substituents [H, CH(CO2Et)2, SEt, Br, SPh, Ph, Cl, NMe2, OH, OSiMe3, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3-substituent (X) by the equations δα= aY+bX and δβ=aX+bY, where a and b are parameters characteristic of X and Y. One-bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α- and the β-carbon atoms of the sulfones show the ‘fore-membered ring sulfone effect’ (α-carbon unusually deshielded, β-carbon unusually shielded), but the α-carbon-hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β-carbon-hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β-effect is observed. Comparison of the chemical shifts of the α-methylene carbon atoms of 3-phenyl-, 3-(β-naphthyl)- and 3-(α-thienyl)-thietes with those of the coresponding sulfones also reveals the ‘four-membered ring sulfone effect’ cis- and trans-3-Substituted thietane 1-oxides may be distinguished by the greater downfield shift for the β-carbon atom in the trans-isomer. 相似文献
16.
V. S. Gurin 《International journal of quantum chemistry》1999,71(4):337-341
Ab initio RHF SCF calculations are used for some small clusters MxXy, where M=Cd, Ag; X=S, I; and x, y≤7. Variation of electronic structure with size for some clusters with the bulklike tetrahedral coordination and with the lower symmetry allows one to predict their possible geometries which are compared with experimental data on the existence of the clusters. The chemical‐bonding factor (the chemical nature of bounded atoms, coordination number for metal and nonmetal atoms, hybridization, etc.) is of more importance for properties of the clusters than is the familiar quantum confinement effect of semiconductor clusters. The essential difference in regularities of small cluster formation is analyzed for CdS‐ and AgI‐based structures. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 337–341, 1999 相似文献
17.
The structures of the SinHm clusters containing 10 to 70 silicon atoms and different numbers of hydrogen atoms are calculated in the MINDO/3 approximation
using the Monte Carlo technique. The geometry optimization of the clusters showed the existence of several structural varieties
that determine the optimal geometry of the clusters differing in size and hydrogen content. Small clusters (n < 20) with various
geometrical configurations often have a hollow structure if the number of silicon atoms in the cluster is more than 12. For
20 ≤ n < 60 and the hydrogen content m ≤ n, hollow spheroidal geometry is most favorable. Staring from n ≈ 56−60, diamond
structures are more favorable. The ratio c = m/n < 1, at which the spheroidal structure remains optimal, decreases with further
increase in n. 相似文献
18.
Yu. G. Papulov O. V. Artyukhova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(8):1455-1457
The methodology of calculations of the physicochemical properties of substituted benzenes C6H6 − p
X
p
, C6H6 − p − q
X
p
Y
q
, ... (X and Y are univalent substituents) and C6H5A, where A = OH (phenol), NH2 (aniline), etc. by the phenomenological methods of chemical structure theory is discussed. 相似文献
19.
Gerhard M. Neumann 《Journal of fluorine chemistry》1973,3(2):209-225
The gas-phase composition of the systems C/F2/Y2 and W/C/F2/Y2(Y = Cl, Br) has been calculated using a digital computer on the basis that thermodynamic equilibrium is attained at the gas/solid interface with tungsten and that the rate of reaction is not kinetically controlled.The partial pressures of the various components, i.e. CX, CX2, CX3, CX4, C2X2, C2X4, C2X6 and WX, WX2, WX4, WX5, WX6, together with those of W, X2 and X (where X = F, Cl, Br) have been evaluated as a function of the temperature and of the halogen concentration in the input gas. While compounds of the type CnXm are quite stable in C/F2/Y2 systems, they are relatively unstable in the presence of solid tungsten where the corresponding tungsten compounds are formed.From the temperature dependence of the mass balance of tungsten, the direction of the chemical transport reactions in these systems may be predicted. In W/C/F2/Y2 systems, two points of inversion exist as in the tungsten-fluorine system. At low temperatures, transport proceeds down the temperature gradient, reversing its direction at moderate temperatures and proceding down the temperature gradient once more at high temperatures. 相似文献
20.
Pavica Planinić Vesna Rastija Siniša Širac Marija Vojnović Leo Frkanec Nevenka Brničević Robert E. McCarley 《Journal of Cluster Science》2002,13(2):215-222
Three new series of mixed-ligand clusters of the [(M6X12)X2(RCN)4] (M=Nb, Ta; X=Cl, Br; R=Et, n-Pr, n-Bu) composition have been prepared. It is supposed that four nitrile molecules and two halogen atoms are coordinated to the terminal octahedral coordination sites of the [M6X12]2+ unit. 相似文献