共查询到20条相似文献,搜索用时 15 毫秒
1.
Michael Dolg 《Theoretical chemistry accounts》2005,114(4-5):297-304
Energy-consistent relativistic pseudopotentials for 3d-transition metals Sc to Ni based on modified valence energies are proposed. The pseudopotentials are adjusted at the finite
difference level within the intermediate coupling scheme with respect to multi-configuration Dirac–Hartree–Fock data based
on the Dirac–Coulomb Hamiltonian with an estimate of the Breit contributions in quasidegenerate perturbation theory. Typically
a few hundred to thousand J levels arising from about 35 to 40 configurations ranging from the anion down to the highly charged
cation are considered as references. It is shown that introducing a small common energetic shift of all valence energies reduces
the errors in the parameter adjustment considerably. Results of highly correlated atomic and molecular test calculations using
large basis sets and basis set extrapolation techniques are presented.
To be submitted to Theoretical Chemistry Accounts (special volume on the occasion of Prof. Dr. H. Stoll's 60th birthday) 相似文献
2.
An extended CNDO formalism for the treatment of large transition metal cluster systems is presented. After a detailed discussion of parametrization it is applied to a family of compounds, namely to Co(CO)
4
–
, Co2(CO)8, Co4(CO)12, Mn2(CO)10.The results can be interpreted in the light of simple electron counting rules and additionally allow detailed insight in bonding capabilities of large metal cluster systems.Bridged and unbridged clusters are compared and the results are extrapolated to surface systems. In the case of Co4(CO)12 two possible stereoisomers of symmetryC
3v
andT
d
are discussed. 相似文献
3.
4.
Lothar Weber 《Angewandte Chemie (International ed. in English)》1996,35(3):271-288
The chemistry of low-valent organophosphorus compounds such as phosphaalkenes and phosphaalkynes has undergone rapid development in the last two decades. This development also includes the coordination chemistry of these species, which can act as versatile ligands in metal complexes. Metallophosphaalkenes are compounds in which one or more of the organic substituents on the P?C unit is replaced by a transition metal complex fragment. Metallophosphaalkenes have emerged from an existence as laboratory curiosities to become a link between main group and organometallic complex chemistry. The great richness of their chemistry not only mirrors the specific properties of the individual building block, but also shows novel and individual traits. Particular examples are cycloadditions of these electron-rich heteroalkenes with electron-deficient alkenes, alkynes, azo, and diazo compounds. These often lead to novel types of reaction and compounds. Metallophosphaalkenes are also important as intermediates in all metal-assisted cyclooligomerizations of phosphaalkynes. 相似文献
5.
Hans-Joachim Freund Bernhard Dick Georg Hohlneicher 《Theoretical chemistry accounts》1980,57(3):181-207
A recently developed extension of the CNDO-method is used to study the electronic structure of a number of binuclear transition metal carbonyls and carboxylates with fourfold or quasi-fourfold symmetry. The results are compared to those available from nonempirical calculations. Special attention is paid to the nature of the metal-metal bond. Connections with qualitative MO-considerations allow a fairly general discussion of metal-metal bonding in binuclear transition metal complexes with basic fourfold symmetry. A few, up to now unknown, but possibly existing, complexes are considered. 相似文献
6.
By use of salt elimination, the transition metal substituted oligosilanes (η5-C5Me4Et)Fe(CO)2SiMe2SiMe2Cl 1, (η5-C5Me4Et)Mo(CO)3SiMe2SiMe2Br 2, (η5-C5Me4Et)Fe(CO)2(SiMe2)6(CO)2Fe(η5-C5Me4Et) 3 and (η5-C5Me4Et)Fe(CO)2(SiMe2)6Br 4 were prepared and characterized. Compound 1 is well crystallized from pentane and its structure has been determined by X-ray diffraction analysis. 相似文献
7.
Hao Feng Yaoming Xie Henry F. Schaefer III 《Journal of organometallic chemistry》2010,695(22):2461-2468
Density functional theory methods (B3LYP and BP86) indicate that the preferred structures for such early transition metal derivatives are (η8-C8H8)M(η4-C8H8) (M = Ti, V, Cr) with one octahapto η8-C8H8 ring and one tetrahapto η4-C8H8 ring. In such structures only 12 of the 16 carbon atoms of the two C8H8 rings are bonded to the metal, leading to 16-, 17-, and 18-electron complexes, respectively, in accord with the experimentally known structures for the Ti and V derivatives. The preferred structures for the Mn and Fe derivatives are (η6-C8H8)M(η4-C8H8) (M = Mn, Fe) with one hexahapto and one tetrahapto C8H8 ring and thus having 17- and 18-electron configurations, respectively, in accord with experimental data on the iron complex. The lowest energy structure for the cobalt complex is (η4-C8H8)Co(η2,2-C8H8) with two different types of tetrahapto C8H8 rings and a 17-electron metal configuration. The nickel complex (C8H8)2Ni appears to prefer a structure with a 16-electron configuration and two trihapto C8H8 rings, similar to the known (η3-C3H5)2Ni rather than a bis(tetrahapto) structure with the favored 18-electron configuration. These theoretical studies indicate that in (C8H8)2M derivatives of the first row transition metals, the number of carbon atoms in the pair of C8H8 rings involved in the bonding to the central metal atom gives the metal atoms 16-, 17-, or 18-electron configurations. 相似文献
8.
9.
《Progress in Surface Science》2001,67(1-8):139-154
The ability for bivalent charge transfer (CT) during hydrogen adsorption on transition metal surfaces and in the course of transition metal hydride formation is discussed. The change of the dipole moment of hydrogen adatoms, caused by transition from a strongly bound adsorption state to a weakly bound state, is demonstrated. The possibility of the CT reversion between the hydrogen adsorbate and the transition metal adsorbent, caused by a change of the surface structure, is described. The CT within the adsorbate, corresponding to the distinguished steps of the process of transition metal hydride formation, is shown. 相似文献
10.
F. Rizzo G.P. Cirrone G. Cuttone A. Esposito S. Garraffo G. Pappalardo L. Pappalardo F.P. Romano S. Russo 《Microchemical Journal》2011,97(2):286-290
In the last years a non-destructive protocol of analysis, based on the combined use of the portable PIXE-alpha (particles induced X-ray emission), the XRF (X-ray florescence) spectrometers and of the new DPAA (deep protons activation analysis) method, was developed at the LANDIS laboratory of the INFN-LNS and IBAM-CNR, in order to characterise late Roman nummi dating from 294 onwards. The main aim of the investigation was the determination of the silver content of the coins produced in different periods of time and the study of the technique used for their manufacturing.The present paper discusses the results obtained from the analysis of 15 coins dated back to 308–311 A.D. produced at Carthago during the domination of the usurper L. Domitius Alexander. The obtained analytical data allowed to make some considerations about the minting of silvered bronze coins during this historical period. 相似文献
11.
The non-toxic and magnetically separable nano-CuFe_2O_4 catalyzed synthesis of symmetrical aryl sulfides by the reaction of thiourea with a wide variety of aryl halides,including aryl chlorides has been reported.Excellent yields of products have been obtained under ligand-free conditions and without the use of any expensive catalyst,such as palladium. 相似文献
12.
Alexey A. Nazarov Mikhail P. Koroteev Christian G. Hartinger Bernhard K. Keppler Eduard E. Nifantev 《Monatshefte für Chemie / Chemical Monthly》2005,136(2):137-146
Summary. The coordination behavior of newly developed bicyclophosphite ligands toward Mo(0), Rh(I), and Pt(II) was studied.Reactions at different ratios of metal to ligand were done. It was found that the ligands act as monodentate ones and form with hexacarbonylmolybdenum(0) complexes with the general formula Mo(CO)5L by replacing only one carbonyl ligand. Coordination experiments toward acetylacetonatodicarbonylrhodium(I) resulted in the formation of undefined compounds. Toward dichlorocyclooctadienylplatinum(II) the monomeric phosphorus ligands act as monodentate ligands forming complexes of the general structure cis-PtCl2L2. All the synthesized platinum-complexes possess cis-configuration (proven by 31P NMR). The corresponding coordination compounds were isolated and characterized by elemental analyses and 1H, 13C, and 31P NMR. 相似文献
13.
《Journal of Coordination Chemistry》2012,65(11):1894-1902
The Co(II), Zn(II), Ni(II), Cu(II), and Fe(II) complexes of 1-phenylbenzimidazole were synthesized and characterized by NMR and elemental analyses. The crystal structures of dichlorobis(1-phenyl-1?H-benzimidazole-κN3 )cobalt(II) and dichlorobis(1-phenyl-1?H-benzimidazole-κN3 )zinc(II) have been determined by single-crystal X-ray diffraction. 相似文献
14.
Summary The first transition row oxides and sulfides are studied using several different levels of theory. The calculations show the bonding mechanism in the sulfides and oxides to be very similar. For the oxides, accurate experimental data allow the theoretical methods to be calibrated. The same level of theory is used to study the sulfides where there is far less experimental information. For ScO through MnO and CuO the coupled cluster singles and doubles technique including a perturbational estimate of the connected triple excitations [CCSD(T)] yields spectroscopic constants (e, e, andD
0) in good agreement with experiment. The triple excitations are found to be very important in achieving this accuracy. For FeO to NiO, the self-consistent-field (SCF) approach yields orbitals that are localized on the metal or oxygen. This appears to cause problems for the single reference techniques; this is discussed in detail for NiO. The complete-active-space SCF/internally contracted averaged coupled pair functional approach (CASSCF/ICACPF) works well for FeO to NiO. The calculation of accurate dipole moments is found to be very difficult. 相似文献
15.
Helmut G. Alt 《Angewandte Chemie (International ed. in English)》1984,23(10):766-782
Alkyltransition-metal complexes play an important role in catalytic processes (e.g. Ziegler-Natta low-pressure polymerization, hydroformylation, Fischer-Tropsch synthesis), in the biochemistry of humans and animals (e.g. coenzyme B12), and in the classical theory of the chemical bond (e.g. multicenter bonding). The chemistry of alkyltransition-metal complexes is 30 years old, but only with the '70s came the understanding necessary for the systematic synthesis of thermally stable representatives of this class of compounds by blocking preferred decomposition pathways—e.g. β-hydrogen elimination—by the introduction of suitable ligands. In this article it is shown that thermally stable alkyltransition-metal complexes can be dealkylated under mild conditions (even at 12 K) with the help of UV light, thus producing highly reactive intermediates which can be trapped and used preparatively. Some alkyl complexes which do not react thermally with unsaturated compounds, e.g. olefins, under the influence of UV light display high activity as polymerization catalysts. 相似文献
16.
The nitration of aromatic compounds can be carried out in the presence of perfluorinated rare earth metal catalyst without halogenated organic solvent. 相似文献
17.
CAI Shu-Hui LIU Chun-Wan*State Key Laboratory of Structural Chemistry Pujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou Fujian China 《中国化学》1996,14(5):385-392
The band structures of Group IVB (Ti,Zr,Hf),VB (V,Nb,Ta) and VIB (Cr,Mo,W) transition metals and some of their carbides and nitrides (TiN,ZrN,HfN,VC,NbC,TaC,VN,NbN,TaN) with NaCl-type (Bl-type) structure have been calculated by using the tight-binding method within the Extended Hiickel approximation (EHT).The energy bands,densities of states and crystal orbital overlap populations are given.The relationship between the bonding properties and the superconducting transition temperatures (Tc) of them is discussed.The influences of various kinds of metallic atoms and changes of bond lengths on Tc are also discussed. 相似文献
18.
《Journal of Coordination Chemistry》2012,65(16):2824-2833
Four new transition metal coordination complexes, [Cd(H2pimdc)2(H2O)2]?·?4H2O (1), [Zn(H2pimdc)2(H2O)2]2?·?7H2O (2), and [M(H2pimdc)2] (M?=?Cu (3) or Ni (4), H2pimdc??=?2-propyl-4,5-imidazoledicarboxylate), have been prepared by conventional synthesis and characterized by elemental analyses, IR, TG, and single-crystal X-ray diffraction. H2pimdc? is a bidentate chelating ligand in 1 and 2, leading to 3-D supramolecular structures through hydrogen bonds. However, H2pimdc? is a tridentate chelating-bridge ligand in 3 and 4, which exhibit 2-D layer structures. Thermal properties and photoluminescence spectra of 1–4 were measured. 相似文献
19.
《Journal of Coordination Chemistry》2012,65(21):3463-3470
Coordination complexes of transition metals (Co, Ni, Cu, Fe, Cr, Ru, Ir, Mn, and Zn) with 6-methoxy-α-methyl-2-naphthalene acetic acid (Naproxen) and triphenylphosphine have been synthesized and characterized by conductance, elemental analysis, UV-Vis, AAS, and FT-IR spectroscopy. The elemental analyses data reveal the presence of 1:1 (metal : ligand) stoichiometry and the IR data suggest that naproxen functions as a bidentate ligand in coordination with transition metals. The anti-inflammatory assays of these complexes have significant effect. 相似文献
20.
Yong Guo Mei-Wei Huang Xiao-Lin Fu Chao Liu Qing-Yun Chen Zhi-Gang Zhao Ben-Zhong Zeng Jiong Chen 《中国化学快报》2017,28(4):719-728
This review summarizes the recent advances in the catalytic syntheses of CF_3S-containing organic molecules using various nucleophilic or electrophilic trifluoromethylthiolating reagents.C-halogen and C—H bonds in various molecules have been transformed to C—SCF_3 bonds by transition-metal-catalyzed reactions,such as cross-coupling of aryl halides.Enantioselective reactions controlled by chiral metal complexes or chiral organocatalysts have afforded many trifluoromethylthiolated chiral architectures,such as β-ketoesters and oxindoles.Very recently,visible-light-induced photoredox trifluoromethylthiolations have been developed,providing versatile CF_3S-containing structures efficiently. 相似文献