XES and quantum chemical investigation of the electronic structure of phthalocyanine complexes MPcH<Subscript>16</Subscript> and MPcF<Subscript>16</Subscript> with M = Cu,Co

The X-ray spectroscopy and X-ray electron study of the electronic structure of unsubstituted phthalocyanines MPcH₁₆ and hexadecafluorophthalocyanines MPcF₁₆ with M = Cu, Co is reported. Quantum-chemical calculation of the electronic structure of these compounds was performed. The calculation was used to analyze the metal-ligand electronic interaction in the complexes. The theoretically calculated energy position and composition of the highest occupied molecular orbitals were compared with experimental data obtained from X-ray fluorescence spectra.     

Electronic structure and catalytic behavior of tungsten carbides

The electronic structure of tungsten carbide was investigated by EHMO semiempirical method. The most stable structure of the carbide was predicted on the basis of binding energy calculations. The W-C bonding is covalent in nature with some charge transfer from the W to the C atoms. The increase in the occupancy of the d shell of the W atoms and the position of the Fermi level may account for the platinum-like catalytic behavior of tungsten carbide.     

Stabilization of the unhybridized Sn2+ stannous ion in the BaClF structure and its characterization by119Sn Mössbauer spectroscopy

In divalent tin halides, when the halogen is small and highly electronegative (F, Cl), the tin valence orbitals are hybridized, the tin(II) non-bonded electron pair is located on one of the hybrid orbitals, and the resulting large electric field gradient gives a large quadrupole splitting. The reaction of barium chloride and tin difluoride in aqueous solutions, for large BaCl₂.2H₂O/SnF₂ ratios (>10) results in the precipitation of a white powdered material, which is identified by X-ray diffraction to be BaCIF. However, Tin-119 Mossbauer spectroscopy shows the material contains a fairly large amount of divalent tin in the Sn²⁺ ionic form, with unhybridized orbitals, like in SnCl₂. Using X-ray diffraction, we have established that Sn²⁺ ions substitute 15% of the Ba²⁺ ions at random, and chemical analysis shows the material has the formula Ba_5.66SnCl_7.30F_6.04 and thus is enriched in chlorine.     

Structure of X-ray photoelectron, emission, and conversion spectra and molecular orbitals of uranium compounds

The fine structure of X-ray photoelectron spectra of uranium compounds in the range of electron binding energies from 0 to ∼50 eV is largely determined by the electrons of the outer and inner valence molecular orbitals arising from the valence atomic shells, including the U6p and Lns low-energy occupied atomic shells. This result is in agreement with the data of the electronic structure calculations of these compounds and confirmed by the nuclear electron (conversion) and X-ray emission spectroscopic investigations. It is shown that the fine structure of X-ray photoelectron spectra associated with the electrons of inner valence molecular orbitals makes it possible to judge the participation of the electrons of the occupied atomic shells in chemical bonding, the structure of the nearest environments of the atom, and the bond lengths in the compounds. The overall contribution of the electrons of these molecular orbitals to the absolute value of binding energy may prove to be comparable to the contribution of the electrons of the outer valence molecular orbitals to atomic bonding. This is a new and important fact in chemistry. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1037–1046, November–December, 1998.     

Experimental and theoretical investigation of the structure and spectral characteristics of bis(4-aza-9-f1uorenone)dibromocopper(II)

The molecular and crystal structure of bis(4-aza-9-fuorenone)dibromocopper(II) [CuL ₂Br₂] was determined by X-ray diffraction. The organic molecule is coordinated in the monodentate fashion with participation of lone electron pairs of heterocyclic nitrogen atoms of 4-aza-9-f1uorenone. The coordination unit parameters were calculated by DFT with PBE functional. The Cu-Br and Cu-N coordination bonds are covalent, the electron pairs of the ligand are transferred to the vacant orbitals of the central ion. The computational methods adequately reproduce the structure of the IR spectrum of the complex.     

Observation of Interference Effects in (e, 2e) Electron Momentum Spectroscopy of SF6 (cited: 1)

Two-dimensional electron density map (2D map) of binding energy and relative azimuthal angle (i.e., momentum) for the outer-valence molecular orbitals of SF₆ has been measured by a highly sensitive electron momentum spectrometer with noncoplanar symmetric geometry at the impact energy of 1.2 keV plus binding energy. The experimental electron momentum profiles for the relevant molecular orbitals have been extracted from the 2D map and interpreted on the basis of the quantitative calculations using the density functional theory with B3LYP hybrid functional. For the outermost F2p nonbonding orbitals of SF₆, the interference patterns are clearly observed in the ratios of the electron momentum profiles of molecular orbitals to that of atomic F2p orbital.     

Chemical bonding interactions in Zr2Al

The electronic structure of Zr₂Al with the Ni₂In-type structure has been calculated by the method of W. Kohn and N. Rostoker (Phys. Rev. 91, 1111 (1954)). The results include densities of states, both total and partial, and resolved according to the angular momentum quantum number, and calculated electron densities presented so as to display directional bonding characteristics of electrons in the valence and conduction regions of energy. It is concluded that: (1) the principal bonding involves aluminum s-type orbitals; (2) the aluminum p-type orbitals are principally nonbonding; and (3) the metallic interactions are principally between zirconium atoms.     

Dinickelaferrocene: A Ferrocene Analogue with Two Aromatic Nickeloles Realized by Electron Back-Donation from Iron

The first example of ferrocene analogues with two transition-metal metallole ligands of the general formula (η⁵-C₄R₄M)₂Fe in a sandwich structure are reported. Specifically, dinickelaferrocene 2 , a type of dimetallametallocene, is efficiently synthesized from the reaction of dilithionickelole 1 with FeBr₂ or FeCl₂, presumably via a redox process, and is subjected to detailed experimental (single-crystal X-ray structural analysis, ICP-OES, magnetometry, ⁵⁷Fe Mössbauer, XPS) and theoretical (MOs, CDA, NICS, ICSS, and AICD) characterizations. Unlike ferrocene and its Cp ligands, the aromaticity of dinickelaferrocene and its nickelole ligands is accomplished by electron back-donation from the Fe 3d orbitals to the π* orbitals of nickelole. Taken together, this work describes a new class of metallaferrocene sandwich complexes and provides a novel approach to effect aromaticity that will contribute to further development of metallocene chemistry.     

Shape resonances and partial photoemission cross sections of solid SF6 and CCl4

Photoelectron energy distribution curves from solid films of SF₆ and CCl₄ have been measured in the photon energy range 10 ? hr ? 40 eV using synchrotron radiation. The binding energies, peak widths and relative partial cross sections have been determined. In the photoelectron spectra a 1:1 correspondence to the gas phase is observed for the occupied molecular orbitals, and a straightforward assignment of the occupied valence bands emerges. Furthermore, the cross sections of the individual orbitals show for both samples great similarities to the gas phase. For SF₆ detailed structures are visible in the cross sections which are only partly interpreted as shape resonances. A new assignment for the 6t_1u shape resonance is proposed and the resonance energies are related to X-ray absorption and electron scattering data. Furthermore a comparison of the total photoemission cross section to the optical reflection spectrum of solid SF₆ is presented. For CCl₄ less structures are ob served in the partial cross sections. They are all interpreted as shape resonances. An energetic scheme of the virtual orbitals is proposed for CCl₄.     

Author index to volume 76

The gas-phase electron affinities of fluorene, biphenyl, its 2-methyl, 2.2′-, 3.3′- and 4.4′-dimethyl derivatives has been measured by means of ETS. The different dihedral angle between the two rings in the various compounds is reflected in the splitting between the in-phase and out-of-phase combinations of the benzene e_2u (π^*) empty orbitals. In the planar fluorene, the electron affinities of the π^* orbitals arising from the benzene e_2u orbitals with a node at the attached carbon atoms indicate a sizeable through-space interaction and a very small net electronic effect of the CH₂ bridge.     

Electronic charge density and mean kinetic energy of lithium orbitals in LiH,LiH+, Li2, Li2+, LiH2+, and Li2H+

The electron density near the lithium nucleus in the species LiH, LiH⁺, Li₂, Li₂⁺, LiH₂⁺, and Li₂H⁺ was analyzed by transforming the SCF molecular orbitals into a sum of atomic contribnutions, for both core and valence orbitals. These “hybrid-atomic” orbitals were used to compare: electron densities, orbital polarizations, and orbital mean kinetic energies with the corresponding lithium atom quantities. Core-orbital electron densities at the lithium nucleus were observed to increase by up to 0.5% relative to the lithium atom 1s orbital. Lithium cores also exhibited polarization but, surprisingly, in the direction away from the internuclear region. Similar dramatic changes were seen in the electron densities of the valence orbitals of lithium: The electron density at the nucleus for these orbitals increased two-fold for homonuclear species and twenty-fold for heteronuclear triatomic species relative to the electron density at the nucleus in lithium atom. The polarization of the valence orbital electronic charge, in the vicinity of the lithium nucleus, was also away from the internuclear region. The mean “hybrid-atomic” orbital kinetic energies associated with the lithium atom in the molecules also showed changes relative to the free lithium atom. Such changes, accompanying bond formation, were relatively small for the lithium core orbitals (within 0.2% of the value for lithium atom). The orbital kinetic energies for the lithium valence electrons, however, increased considerably relative to the lithium atom: By a factor of about 2 in homonuclear diatomics, by a factor of 7 in heteronuclear diatomics, and by a factor of 11 in the triatomic species. In summary, the total electronic density (core plus valence) at the lithium nucleus remained remarkably constant for all of the species studied, regardless of the effective charge on lithium. Thus, the drastic changes noted in the individual lithium orbitals occurred in a cooperative fashion so as to preserve a constant total electron density in the vicinity of the lithium nucleus. In all cases, bond formation was accompanied by an increase in the orbital kinetic energy of the lithium valence orbital. We suggest that these two observations represent important and significant features of chemical bonding which have not previously been emphasized.     

六聚同多酸阴离子M_6O_(19)~(n-)(M=Mo,W,n=2;M=Nb,Ta,n=8)电子结构和化学性质的密度泛函理论研究

采用B3LYP方法在LanL2DZ水平上计算了六聚同多阴离子 (M6On-19,M =Mo和W ,n =2 ;M =Nb和Ta ,n =8)的电子结构 ,分析了它们的前线轨道、分子静电势 (MEP) .计算结果表明 ,Nb6O8-19和Ta6O8-19是电子给体 ,而Mo6O2 -19和W6O2 -19则是电子受体 ,这与它们在溶液中具有不同的化学性质是一致的     

Experimental and theoretical binding energy spectra and momentum distributions for the valence orbitals of H2O

The binding energy spectra (10–46 eV) and momentum distributions of the valence orbitals of H₂O have been measured using a new high-sensitivity binary (e,2e) electron spectrometer employing position-sensitive detectors. The binding energy spectrum shows a previously unreported feature at = 27 eV which is shown to be associated with the (2a₁)^?1 ionization process. The region between 25 and 46 eV is compared with previous (e,2e) and X-ray photoelectron measurements as well as with several existing and new many-body calculations indicating a splitting of the 2a₁ ionization pole strength. In addition the separate momentum distributions of the three outer valence orbitals of H₂O have been obtained from deconvoluted binding energy spectra run at a series of azimuthal angles. The results, which show considerably improved signal-to-noise ratio over earlier measurements using single-channel instrumentation are compared with spherically averaged momentum distributions calculated with a variety of wavefunctions.     

Special Features of the Geometry of the 2,2,2,4,4,4-Hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane Molecule and Its Electron Distribution According to Data of ab initio Calculations

The results of a nonempirical calculation of the 2,2,2,4,4,4-hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane (Cl₃PNCH₃)₂ molecule by the RHF 6-31G(d) method are in agreement with the data of X-ray structural analysis of this compound. Calculated ³⁵Cl NQR frequencies for axial and equatorial chlorine atoms are close to the experimental values. The population of the orbitals of the lone electron pairs and the p orbitals of the equatorial Cl atoms were significantly lower than those of the axial atoms. Among the MO there was no MO corresponding to a three-center bond involving a P atom and axial Cl and N atoms.     

One electron orbitals intrinsic to the reduced hamiltonian

One electron orbitals are determined from the reduced hamiltonian by a simple one-step diagonalization. These reduced hamiltonian orbitals (RHO's) are uniquely determined and virtual orbitals obtained in this procedure are on a par with filled orbitals. These RHO's appear well suited for CI calculations. Minimum basis set calculations are presented for H₂O and compared with similar SCF studies.     

An ab initio evaluation of the role of p,π interaction: I. Ethylene derivatives

The RHF/6-311G(d) and MP2/6-311G(d) calculations with full geometry optimization were performed for XCH=CH₂ molecules (X = F, Cl, Br, CH₃, CH₂CH₃, CH₂F, CHO). The p _y electron density distribution in these molecules and the bonding molecular orbitals formed by the p _y orbitals of atoms of the planar fragment of these molecule (atomic orbitals whose symmetry axes are perpendicular to this plane) are not determined by the p,π conjugation between the lone electron pair of the heteroatom in substituent X and π electrons of the C=C bond. Changes in the population of the p _y orbitals of the halogen and carbon atoms in going from X = F to X = Cl and Br are not associated with changes in the extent of this p,π interaction. Taking into account the electon correlation in the MP2 method does not noticeably alter the features of the electron density distribution in these molecules estimated by restricted Hartree-Fock calculations.     

Quantum yield spectra of vanadium in tetrahedral [VO4]3− complexes

Conclusions Studies of VL_2,3 quantum yield spectra and analysis of theoretical and experimental data were used to give information on the processes proceeding during the emission and absorption of the X-ray VL-radiation. It is very probable that the X-ray L₃-absorption processes in compounds where the 3d-metal has the highest valence proceed in the presence of an additional electron on one of the vacant orbitals (for tetrahedral complexes on the 2e-MO). This assumption can confirm the hypothesis on the reemissional transitions and explain the energy divergence between the VL-emission and absorption spectra.Institute of Physics of Metals, Ural Branch Academy Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 1, pp. 81–86, January–February, 1988.     

The involvement of metal-to-CO charge transfer and ligand-field excited states in the spectroscopy and photochemistry of mixed-ligand metal carbonyls. A theoretical and spectroscopic study of [W(CO)(4)(1,2-ethylenediamine)] and [W(CO)(4)(N,N'-bis-alkyl-1,4-diazabutadiene)

A new interpretation of the electronic spectroscopy, photochemistry, and photophysics of group 6 metal cis-tetracarbonyls [M(CO)(4)L(2)] is proposed, that is based on an interplay between M --> L and M --> CO MLCT excited states. TD-DFT and resonance Raman spectroscopy show that the lowest allowed electronic transition of [W(CO)(4)(en)] (en = 1,2-ethylenediamine) has a W(CO(eq))(2) --> CO(ax) charge-transfer character, whereby the electron density is transferred from the equatorial W(CO(eq))(2) moiety to pi orbitals of the axial CO ligands, with a net decrease of electron density on the W atom. The lowest, emissive excited state of [W(CO)(4)(en)] was identified as a spin-triplet W(CO(eq))(2) --> CO(ax) CT excited state both computationally and by picosecond time-resolved IR spectroscopy. This state undergoes 1.5 ps vibrational relaxation/solvation and decays to the ground state with a approximately 160 ps lifetime. The nu(CO) wavenumbers and IR intensity pattern calculated by DFT for the triplet W(CO(eq))(2) --> CO(ax) CT excited state match well the experimental time-resolved spectrum. For [W(CO)(4)(R-DAB)] (R-DAB = N,N'-bis-alkyl-1,4-diazabutadiene), the W(CO(eq))(2) --> CO(ax) CT transition follows in energy the W --> DAB MLCT transition, and the emissive W(CO(eq))(2) --> CO(ax) CT triplet state occurs just above the manifold of triplet W --> DAB MLCT states. No LF electronic transitions were calculated to occur in a relevant energetic range for either complex. Molecular orbitals of both complexes are highly delocalized. The 5d(W) character is distributed over many molecular orbitals, while neither of them contains a predominant metal-ligand sigma 5d(W) component, contrary to predictions of the traditional ligand-field approach. The important spectroscopic, photochemical, and photophysical roles of M(CO(eq))(2) --> CO(ax) CT excited states and the limited validity of ligand field arguments can be generalized to other mixed-ligand carbonyl complexes.