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1.
The photoelectron spectra of several transition-metal carbonyl complexes of norbornadiene and mesitylene have been measured. The data for the norbordiene complexes have been compared with those reported previously for norbornadieneiron tricarbonyl. The shifts in energies of the π orbitals of the ligands introduced by the metal carbonyl moieties are remarkably insensitive to the choice o0f transition metal or geometry of the complex. However, the characters of the metal d-orbital ionization bands are markedly affected by the choice of ligand.  相似文献   

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3.
Summary Mixed ligand diglycinatocopper(II) complexes of the Cu(glygly)L·nH2O type, where glygly stands for [NH2-CH2 CONCH2CO2]2– and L for imidazole (n = 1.5), N-methylimidazole (n = 1), 2-methylimidazole (n = 2), 4-methylimidazole (n = 2), 4-phenylimidazole (n = 2), N-acetylhistamine (n = 2) and NH3 (n = 2), were prepared and characterized by elemental analyses, i.r., vis. and e.p.r. spectroscopic measurements. The molecular structure of [Cu(glygly)(achmH)]·2H2O (achmH = acetylhistamine) was determined using three dimensional XRD data. The structure consists of distorted square planar [Cu(glygly)-(achmH)] units interconnected via the peptide oxygen at the apex to complete a square pyramidal structure, Cu—O-(peptide) 2.477(2) Å. The H2O molecules, not binding directly to the copper ion, involve in intermolecular hydrogen bonding with the copper units. The dianionic glygly ligand and the imidazole ring bind strongly to the central copper ion with Cu—N(amino) 2.045(6) Å, Cu—N-(peptide) 1.891(5) Å, Cu—O(carboxylate) 2.001(4) Å and Cu—N(imidazole) 1.956(5) Å. The dihedral angle between the imidazole nucleus and the CuN3O xy plane is 6.0°. Similar structures with a CuN3O coordination plane are proposed for the imidazole complexes, based on spectroscopic data. The bonding properties of the glygly ligand and the unidentate imidazole ligands are elucidated and discussed with reference to the electronic structures of the complexes deduced from Gaussian analyses.  相似文献   

4.
The electronic structures of ScB2, TiB2, VB2, CrB2 and MnB2 have been examined by theoretical investigations. The band structures and accompanying density-of-states plots are presented. The calculated Fermi Levels are, ?5.6 eV (ScB2), ?5.7 eV (TiB2), ?6.3 eV (VB2), ?7.1 eV (CrB2), and ?7.8 eV (MnB2). The valence bands at the Fermi Edge are localised about the metal 3d orbitals. The charge distributions of the diborides are obtained from the density-of-states plots and show that the metals possess the following positive charges: Sc (+2.28), Ti (+1.99), V (+1.85), Cr (+1.52), and Mn (+1.08). The bonding within the diborides is explained with the help of solid-state calculations at a Special Point and quasi-molecular cluster calculations.  相似文献   

5.
The geometric and electronic structures of a series of hypothetical compounds of the types CpM(C13H9N) and (CO)3M(C13H9N) (M = first row transition metal and C13H9N = 7,8-benzoquinoline) have been investigated by means of density functional theory (DFT). The benzoquinoline ligand can bind to the metal through η16 coordination modes, adopting structures of types a, b and c, in agreement with the electron count and the nature of the metal. In the investigated species, the most favored closed-shell count is 18-MVE, except for the Ti and V models which prefer the open-shell 16-MVE configuration. This study has shown the difference in the coordination ability of this heteropolycyclic ligand and coordination of the inner C6 ring is less favored than the outer C6 and C5N rings, in agreement with the π-electron density localization.  相似文献   

6.
Summary Complexes of overall formula TiAl2X8 · Ar (X = Cl, Br or I, Ar = benzene or hexamethylbenzene) and the complexes containing various amounts of Br or I in addition to Cl were prepared both by a direct synthesis — the reduction of titanium tetrahalide by aluminium in the aromatic solvent and in excess of the corresponding aluminium halide — and by halogen exchange between the complexes and aluminium halides. The interpretation of the electronic spectra of the complexes is given on the assumption of pseudooctahedral symmetry of the ligand field. The values of 10 Dq and B obtained are compatible with the assignment.  相似文献   

7.
Two transition-metal oxide diatomic cations, VO+ and MoO+ are considered in this article. Ground- and excited-state properties of the cations are derived from spin-polarized DF calculations, including spectroscopic constants and metal–oxygen bonding features. A set of ionization potentials are calculated and, for vanadium oxide, compared with photoelectron spectroscopy data and a few available ab initio calculations. All calculated properties are close to experiment, the agreement being much better than for other traditional quantum chemical calculations. Present results together with our earlier findings for neutral molecules provide an excellent confirmation of the good performance of DFT in the case of transition-metal systems. © 1995 John Wiley & Sons, Inc.  相似文献   

8.
We report the preparation and electrochemical studies of a systematic series of mono- and di-nitro-substituted 2,2'-bipyridine (bipy) compounds [x-NO(2)-bipy (x = 3,4) and x,x'-(NO(2))(2)-bipy (x,x' = 3, 4, 5)] and their complexes with platinum(II), [Pt(x-NO(2)-bipy)Cl(2)] and [Pt(x,x'-(NO(2))(2)-bipy)Cl(2)]. The effect of the number and substitution pattern of the nitro groups on the low-lying acceptor molecular orbitals (involved in charge transfer transitions) is probed by in situ UV/Vis/NIR and EPR spectroelectrochemical methods, supported by DFT calculations. The LUMOs of x-NO(2)-bipy (x = 3-5) are largely localised on the NO(2)-pyridyl moiety; this is also true of their {PtCl(2)} complexes but with a small but significant shift of electron density from the nitro groups. The LUMOs of x,x'-(NO(2))(2)-bipy with x = 3 and 5 are delocalised over both NO(2)-pyridyl rings, but for 4,4'-(NO(2))(2)-bipy is localised on a single NO(2)-pyridyl ring. In all cases the LUMO of the [Pt(x,x'-(NO(2))(2)-bipy)Cl(2)] complexes is delocalised over both nitro-pyridyl rings. For all complexes, the 4(4') derivatives allows greatest overlap with metal valence orbitals in the LUMO.  相似文献   

9.
10.
A new parameterization for the first transition metal has been proposed in the framework of CNDO /2 method. We carried out CNDO /2 calculation of hexamine complexes [M(NH3)6]2+ and hexa-aquo complexes [M(OH2)6]2+ in the high spin state where M = Mn, Fe, Co, Ni, and Cu, using new parameters. It is shown that the calculated order of binding energy is Mn? L < Fe? L < Co? L < Ni? L ≈ Cu? L (where L means the ligand), and is in good agreement with experiment. We discussed how the orbital nodes affect the nature of bonding between metal and ligand.  相似文献   

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12.
A method of identification of the electronic structure of stable nitroxide radical complexes with organic ligands is developed. The idea of this approach is that the concentration dependences of the paramagnetic shifts and line widths of the NMR spectra of two ligands in solution depend on whether these ligands form complexes with the same radical orbital or with different orbitals. In the latter case the complexation of one ligand should not influence the paramagnetic shift and line broadening of another ligand molecule present in the solution. In contrast, in the former case such influence should exist since both ligands are in competition. On this basis different schemes of complexation are considered and theoretical expressions for paramagnetic shifts and line widths are derived that show what kind of experimental data is required to identify the structure of the complex. The theory developed can be generalized to other paramagnetic complexes of radicals, ions and molecules.  相似文献   

13.
The xenon-fluoride bond dissociation energy in XeF3- has been measured by using energy-resolved collision-induced dissociation studies of the ion. The measured value, 0.84 +/- 0.06 eV, is higher than that predicted by electrostatic and three-center, four-electron bonding models. The bonding in XeF3- is qualitatively described by using molecular orbital approaches, using either a diradical approach or orbital interaction models. Two low-energy singlet structures are identified for XeF3-, consisting of Y- and T-shaped geometries, and there is a higher energy D3h triplet state. Electronic structure calculations predict the Y geometry to be the lowest energy structure, which can rearrange by pseudorotation through the T geometry. Orbital correlation diagrams indicate that that ion dissociates by first rearranging to the T structure before losing fluoride.  相似文献   

14.
We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.  相似文献   

15.
A self-consistent APW band structure calculation has been performed for TiN0.75, assuming long-range ordered vacancies at the nonmetal lattice sites. Two different kinds of titanium atoms occur in this model: Ti[6] atoms that are octahedrally surrounded by six nitrogen atoms and Ti[4] atoms that have only four nitrogen neighbors and are adjacent to two vacancies. The model structure can be described as Ti[4]3Ti[6]N3N, where □N denotes a nitrogen vacancy. In the densities of states, two sharp vacancy peaks have been found which are not present in stoichiometric TiN. The bonding situation is discussed by means of electron density plots. It is found that the chemical bonding is characteristically influenced by the introduction of vacancies. The calculated XPS and K XES are shown to be in good agreement with the experimental spectra.  相似文献   

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17.
Twenty-four copper(II) complexes have been prepared with ethylenediamine, propylendiamine, stilbenediamine and tetramethylenediamine with different axial ligands. Their absorption spectra (190–800 nm) have been measured in solution. Dq, Ds, Dt and Dqz crystal field parameters for these complexes have been obtained and used in the evaluation of their possible configuration. In particular, for the Cu(stien)2(F3CCOO)2 complex the CuN distance is obtained from spectroscopic and magnetic data.  相似文献   

18.
We have previously shown that a division of the f‐shell into two subsystems gives a better understanding of the cohesive properties as well the general behavior of lanthanide systems. In this article, we present numerical computations, using the suggested method. We show that the picture is consistent with most experimental data, e.g., the equilibrium volume and electronic structure in general. Compared with standard energy band calculations and calculations based on the self‐interaction correction and LDA + U, the f‐(non‐f)‐mixing interaction is decreased by spectral weights of the many‐body states of the f‐ion. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005  相似文献   

19.
Palladium(II) complexes attract great attention due to their remarkable catalytic and biological activity. In the present study X-ray characterization, UV-Vis and Time-Dependent Density Functional Theory (TD-DFT) calculations for six PdCl(2)(XPy)(2) complexes (where: Py = pyridine; X = H, CH(3) or Cl) were applied in order to investigate substituent effects on their crystal structures and electronic properties and to combine the results with their catalytic and cytotoxic activity. The structures of complexes PdCl(2)(3-MePy)(2), PdCl(2)(4-MePy)(2) and PdCl(2)(2-ClPy)(2), have been described for the first time and we compared our results with available data for the whole series of six complexes. All compounds exhibit a square planar coordination geometry in which the palladium ion coordinates two nitrogen atoms of pyridine ligands and two chlorine atoms in trans positions. For complexes with ortho substituted XPy ligands a cis disposition of substituents takes place, whereas for other ligands: 3-MePy and 3-ClPy--the substituents are in trans positions. For XPy the energies of π-π* and n-π* transitions depend on the position and nature of the X substituent in the XPy ring. After complex formation a hipsochromic shift (24-34 nm) of π-π* and a bathochromic shift of n-π* bands are observed. The UV-Vis spectra of PdCl(2)(XPy)(2) confirm that square planar coordination geometry of complexes I-VI and two dπ-π* transitions are expected. With the help of the TD-DFT calculations we proved that dπ-π* transitions in solutions of PdCl(2)(XPy)(2) complexes result from MLCT (metal-to-ligand charge transfer) with contribution from chlorine atoms to palladium. We also studied substituent effects on cytotoxic properties of Pd(II) complexes against the human breast cancer cell line MCF7, the human prostate cancer cell line PC3, and the human T-cell lymphoblast-like cell line CCRF. The studied complexes were the most active against the CCRF cell line and less or even no cytotoxic effect was observed for PC3 cells. Complexes with MePy ligands showed increased cytotoxic activity compared to unsubstituted pyridine ligands.  相似文献   

20.
The electronic structure of SCIF5 is computed within the framework of the CNDO/2 approximation on the basis of Kewley's microwave geometrical data and is compared with our previous results on SF6. The charge distribution and the value of the dipole moment are discussed as a function of the F-S-Fax angle and an inversion of the net charge on Cl is observed when passing through the 95° value for (F-S-Fax) angle.  相似文献   

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