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111.
Ab initio molecular orbital theory and density functional theory have been employed to study N14 cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N14 is a C
2h
-symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become. 相似文献
112.
Koridze A. A. Kuklin S. A. Petrovskii P. V. Dolgushin F. M. Ezernitskaya M. G. 《Russian Chemical Bulletin》2002,51(2):350-353
The Os3(-H)2(CO)7(-C6H4){3-Ph2PCH2P(C6H4)Ph} complex, which was isolated from the products of thermolysis of Os3(CO)10(-dppm) (dppm is Ph2PCH2PPh2) in toluene, was characterized by X-ray diffraction analysis. Protonation of the resulting complex with trifluoroacetic acid afforded the cationic complex [Os3(-H)3(CO)7(-C6H4){3-Ph2PCH2P(C6H4)Ph}]+. 相似文献
113.
Deprotonation of Mn2(μ-H)(μ-PR2)(CO)8 (R = Ph Cy) for Synthesis of Heteronuclear Manganese-Gold Clusters with Mn2Aun Cores (n = 1–3) The dimanganese complexes Mn2(μ-H)(μ-PR2)(CO)8 (R = Ph, Cy) have been deprotonated with 1,8-diazabicyclo[5.4.0]undec-7-en (DBU) in tetrahydrofuran solution at 20°C to give the anions [Mn2(μ-PR2)(CO)8]?, which were isolated as tetraethylammonium salts. Both dimanganese complexes and the related anions were measured by cyclic voltammetry. The treatment of the aforementioned dimanganese complexes in thf solution with Lir' (R =Me, Ph) and subsequently with PPh3AuCl gave at 20°C three types of products: Mn2(μ-PR2(CO)8(AuPPh3),Mn2(μ-PR2)(μ-C(R′)O)(CO)6-(AuPPh3)2 and Mn2(μ-PR2)(CO)6(AuPPh3)3. The newly prepared substances were characterized by means of IR-, UV/VIS, 31P NMR data. The results of single X-ray analyses showed for the three-membered metal ring compound Mn2(μ-PPh2)(CO)8(AuPPh3) an uni-fold bridged σ(Mn? Mn) bond length of 306.7(3) pm, the metallatetrahedron complex Mn2(μ-PPh3)(μ-C(Ph)O(CO)6(AuPPh3)2 a twofold bridged σ(Mn? Mn) bond length of 300.6(4) pm and the trigonal-bipyramidal cluster Mn2(μ-Pph2)(CO)6(AuPPh3)3 an uni-fold bridged π(Mn? Mn) bond length of 274.7(3) pm. The Mn? Au bonds of these substances are accompanyied by semi-bridging CO ligands which are signified through short Au…C contact lengths in the range of 251 to 270 pm. In the substance with the Mn2Au2 metallatetrahedron core exists, additionally, such a contact with the acylic C atom of C(Ph)O bridging group of 263.4(18) pm. Such contact lengths were compared for corresponding dimanganese and dirhenium complexes. 相似文献
114.
The reactions of Re2X4(-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) with H2S in THF afford the dirhenium (III) complexes Re2(-H)(-SH)X4(-dppm)2, the first examples of the oxidative addition of an S-H unit across an electron-rich metal-metal triple bond. The bromide complex Re2(-H)(-SH)Br4(-dppm)2 (C2H5)2O crystallizes in the space group P21/n witha=16.631(2) Å,b=15.967(3) Å,c=19.904(2) Å, =92.698(7)°,V=5279(2) Å3, andZ=4. The structure which was refined toR=0.053 (R
w=0.070) for 4903 data withI>3.0(I), shows the presence of an edge-shared bioctahedral geometry with a very short Re-Re distance of 2.4566(7) Å. While the hydrogen atoms of the -H and -SH ligands were not located in the X-ray structure determination, their presence is confirmed by IR and1H NMR spectroscopy. 相似文献
115.
Dimitri E Khoshtariya Achim Zahl Tina D Dolidze Anton Neubrand Rudi van Eldik 《Chemphyschem》2004,5(9):1398-1404
Difference and double-difference near-infrared DO-D and HO-H stretching overtone (2nuOD and 2nuOH) spectroscopy and a rigorous (physically substantiated) band deconvolution technique were applied to reveal three different kinds of inherent (interstitial) structures of liquid water, which determine its high density (compared to ice lh under ambient conditions), its compressibility (under hydrostatic pressure, up to 300MPa), and its high fragility (manifested under temperature variation). Our data processing allowed the rigorous discrimination of up to six vibrational components. On the basis of an extensive comparative analysis combined with available structural data (X-ray and neutron scattering) and molecular dynamics (MD) simulations for liquid water, as well as with experimental and computed data for small non-tetrahedrally arranged water clusters, the major four components could be ascribed to: i) The basic lh icelike substructure; ii) the temperature-dependent remote interstitial "defects" due to tetrahedral displacements (primarily responsible for transport properties); iii) the interstitial "defects" most probably arranged in quasiplanar noncyclic tetramers (totally absent in the ice structure); and iv) the interstitial "defects" formed with increasing pressure, probably arranged in cubic water octamers and composed of two pairs of noncyclic and cyclic tetramer fragments. The latter structures include, essentially, bent hydrogen bonds stabilized by resonance effects. 相似文献
116.
Serdar Öğüt Juan C. Idrobo Julius Jellinek Jinlan Wang 《Journal of Cluster Science》2006,17(4):609-626
We examine low-energy isomeric forms, static polarizabilities, and optical absorption spectra of Ag
n
, n = 2–8, and Au
n
, n = 2–3, clusters using first principles computations within the static and time-dependent versions of the density functional theory. The noticeable decrease in the static polarizabilities of Ag7 and Ag8 compared to the values characteristic of Ag
n
, n = 2–6, is correlated with the transition from two-dimensional to three-dimensional structures at n = 7. The optical spectra computed within the time-dependent local density approximation for the most stable structures are in good agreement with the available experimental data and the results of earlier theoretical studies. Optical spectra of higher-energy isomers typically present features that are not observed in the experimental spectra. The d electrons affect the spectra of noble metal clusters by quenching the oscillator strengths through screening of the s electrons and by getting directly involved in the excitations. Due to the larger s–d hybridization in Au compared to Ag, these effects are more pronounced in Au
n
clusters. 相似文献
117.
The historical background of and the incentive for using ruthenium carbonyl clusters as homogeneous catalysts are outlined.
Keeping in view the possible solutions the uncertainties arising from declusterification and metal colloid formation are discussed.
All ruthenium cluster-catalysed reactions are broadly classified as reactions with or without carbon monoxide as one of the
reactants and the basic differences between such reactions are highlighted. Some of the factors of special relevance to cluster-catalysed
reaction systems are mentioned. The reactions involving carbon monoxide are then discussed. These include water-gas-shift
reaction, carbon monoxide hydrogenation, hydroformylation, reductive carbonylation of nitrobenzene and other carbonylation
reactions. Hydrogenation, transfer hydrogenation, isomerisation and a few other reactions are then discussed. For all these
reactions, special emphasis is laid on well-characterised cluster complexes that have been proposed as catalytic intermediates.
Finally an attempt has been made to identify the path that future research in cluster catalysis is likely to follow. 相似文献
118.
O. A. Kizas V. V. Krivykh V. V. Vorontsov A. A. Koridze 《Russian Chemical Bulletin》1993,42(6):1102-1103
Protonation of triosmium clusters Os3(-H)(CO)9(3-,2-CC-R) (R=CMe2OH, C(Me)=CH2) affords a cationic complex containing a six-electron propargyl ligand which has been detected for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1144–1145, June, 1993. 相似文献
119.
As a model for a binary alloy undergoing an unmixing phase transition, we consider a square lattice where each site can be either taken by an A atom, a B atom, or a vacancy (V), and there exists a repulsive interaction between AB nearest neighbor pairs. Starting from a random initial configuration, unmixing proceeds via random jumps of A atoms or B atoms to nearest neighbor vacant sites. In the absence of any interaction, these jumps occur at jump rates
A and
B, respectively. For a small concentration of vacancies (c
v=0.04) the dynamics of the structure factorS(k,t) and its first two momentsk
1(t),k
2
2
(t) is studied during the early stages of phase separation, for several choices of concentrationc
B of B atoms. Forc
B=0.18 also the time evolution of the cluster size distribution is studied. Apart from very early times, the mean cluster sizel(t) as well as the moments of the structure function depend on timet and the ratio of the jump rates (=
B/
A) only via a scaled timet/(). Qualitatively, the behavior is very similar to the direct exchange model containing no vacancies. Consequences for phase separation of real alloys are briefly discussed. 相似文献
120.
The cluster density function of independent percolation in ad-dimensional lattice is considered. For eachn, it is shown that(p) has finitenth leftderivative at critical probabilityp
c ifd is sufficiently large. This result agrees with the Bethe lattice approximation, where thenth one-sided derivative of(p) is bounded atp
c for alln. 相似文献