Unrestricted CNDO-MO calculations. II. MnO 4 2− and CrO 4 3−

The electronic structures of the tetrahedral molecule ions MnO ₄ ^2– and CrO ₄ ^3– have been investigated within an unrestricted CNDO-MO approximation [Theoret. Chim. Acta (Berl.)20, 317 (1971)]. Calculations assuming the unpaired electron occupies the 3a ₁, 2e, and 4t2 molecular orbitals indicate that the 3a ₁ and2e orbitals have similar orbital energies and that the 4t ₂ orbital is at a higher energy. The experimentally indicated2e orbital for the unpaired electron is obtained with expanded O^1– type atomic orbitals for oxygen and valence metal orbitals of the expanded 3d and plus one ion 4p types. The metal 4s orbitals must be held to the neutral atom type. The optimum valence orbitals above with a slightly contracted 4s type metal orbitals yield the minimum total energy and places the unpaired electron in the 3a ₁ orbital. Since the contracted 4s metal orbital produces results that are not in agreement with experimental data, the method used apparently does not adequately take into account the increased electron-electron repulsions that contracted 4s orbitals produce.     

Compact basis sets for LCAO-LSD calculations. Part I: Method and bases for Sc to Zn

A method for preparing compact orbital and auxiliary basis sets for LCAO-LSD calculations has been developed. The method has been applied to construct basis sets for first row transition metal atoms from Sc to Zn for the 3d^n?14s¹ and 3d^n?24s² configurations. The properties of different expansion patterns have been tested in atomic calculations for the chromium atom.     

Why do the second row transition metal atoms prefer 5s14dm+1 to 5s24dm?

Numerical Hartree-Fock (NHF) calculations have been performed for 332 ground and low-lying excited states of the fifth period atoms Rb through Xe, with our special interest in the states arising from the 5s ²4d ^m , 5s ¹4d ^m +1, and 5s ⁰ 4d ^m +2 configurations of the second row transition metal atoms. Among various properties, orbital energies and mean values ofr of the outermost orbitals of each symmetry are presented as well as total energies. It is discussed in some detail why the second row transition metal atoms have a tendency to prefers ¹ d ^m +1 as the ground configuration in contrast to the preferreds ² d ^m configuration in the first row transition metal atoms. Our systematic NHF computations reported in this and the previous papers conclude that the Hartree-Fock method correctly predicts the experimental ground state of the atoms He through Xe with the sole exception for Zr.     

Identification of the Most Stable Sc2C80 Isomers: Structure,Electronic Property,and Molecular Spectra Investigations

A systematic density functional theory investigation has been carried out to explore the possible structures of Sc₂C₈₀ at the BMK/6‐31G(d) level. The results clearly show that Sc₂@C₈₀‐I_h, Sc₂@C₈₀‐D_5h, and Sc₂C₂@C₇₈‐C_2v can be identified as three isomers of Sc₂C₈₀ metallofullerene with the lowest energy. Frontier molecular orbital analysis indicates that the two Sc₂@C₈₀ isomers have a charge state as (Sc³⁺)₂@C₈₀^6?and the Sc₂C₂@C₇₈ has a charge state of (Sc³⁺)₂C₂^2?@C₇₈^4?. Moreover, the metal‐cage covalent interactions have been studied to reveal the dynamics of endohedral moiety. The vertical electron affinity, vertical ionization potential, infrared spectra and ¹³C nuclear magnetic resonance spectra have been also computed to further disclose the molecular structures and properties.     

Introducing a New d0 Sc3+ Asymmetric Ion for Functional Materials: Large Birefringence Enhancement by ScO6 in Ba3Sc2(BO3)4

Transition metal ions with d⁰ electronic states (Ti⁴⁺, Zr⁴⁺, Nb⁵⁺ and Ta⁵⁺) are widely investigated as functional materials. This work first illustrates that Sc³⁺ ion, long-time ignored, displays a second-order Jahn-Teller (SOJT) effect similar to asymmetric oxide-coordinated transition metal ions, thus providing a new ground to seek for asymmetric functional materials with enhanced performances. In Ba₃Sc₂(BO₃)₄, BO₃ groups are parallelly arranged, satisfying the ideal arrangement to produce large birefringence. Importantly, distorted octahedral ScO₆ with Sc³⁺ ion in its d⁰ electronic state enlarges birefringence unexpectedly up to 0.149 @ 550 nm, which is larger than previously reported borates containing solely BO₃, even to B₃O₆ units. Subsequently, the SOJT influence of distorted ScO₆ octahedra on birefringence is verified by a comparison between experimental data and theoretical calculations. In addition, Ba₃Sc₂(BO₃)₄ also displays a high transmittance in the range of 230 nm–3.5 μm with a UV cut-off wavelength at 198 nm and a large laser induced damage threshold (2.7 GW/cm²), comparable to α-BaB₂O₄. Above characteristics imply that the title compound may be a promising birefringent material.     

Potential energy curves for NiH and NiH2

The potential energy curves for the NiH and linear HNiH molecules resulting from the 3d⁸4s² and 3d⁹4s configuration of nickel are calculated using the unrestricted Hartree–Fock and perfect pairing generalized valence bond methods. NiH bonding in the 3d⁸4s² configuration is by means of an sp hybrid orbital which comes from the 4s² shell leaving a singly occupied nonbonding orbital free to bond to another hydrogen atom. The bond to the 3d⁹4s configuration contains primarily the 4s orbital leaving an empty orbital in the nickel 3d shell which in turn bonds very weakly with another hydrogen. These results are compared to similar studies of the hydrogen atom on Sc, Mn and Cu and some implications for hydrocarbon catalysis are considered.     

Density matrix averaged atomic natural orbital (ANO) basis sets for correlated molecular wave functions

Generally contracted basis sets for the first row transition metal atoms Sc-Zn have been constructed using the atomic natural orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANOs are constructed by averaging over the three electronic configurationsd ⁿ ,d ^n–1 s, andd ^n–2 s ² for the neutral atom as well as the ground state for the cation and the ground state atom in an external electric field. The primitive sets are 21s15p10d6f4g. Contraction to 6s5p4d3f2g yields results that are virtually identical to those obtained with the corresponding uncontracted basis sets for the atomic properties, which they have been designed to reproduce. Slightly larger deviations are obtained with the 5s4p3d2f1g for the polarizability, while energetic properties still have only small errors. The design objective has been to describe the ionization potential, the polarizability and the valence spectrum as accurately as possible. The result is a set of well-balanced basis sets for molecular calculations, which can be used together with basis sets of the same quality for the first and second row atoms.     

Terminal Molybdenum Phosphides with d Electrons: Radical Character Promotes Coupling Chemistry

A terminal Mo phosphide was prepared through the group transfer of both P and Cl atoms from chloro‐substituted dibenzo‐7λ³‐phosphanorbornadiene. This compound represents the first structurally characterized terminal transition‐metal phosphide with valence d electrons. In the tetragonal ligand field, these electrons populate an orbital of d_xy parentage, an electronic configuration that accommodates both metal d electrons and a formal M≡P triple bond. Single‐electron oxidation affords a transient open‐shell terminal phosphide cation with significant spin density on P, as corroborated by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) characterization. Facile P−P bond formation occurs from this species through intermolecular phosphide coupling.     

C−H Activation and Olefin Insertion in d8 and d0 Complexes: Same Elementary Steps,Different Electronics

Metallocene alkyl complexes with d⁰ electron configuration and d⁸-configured square planar α-diimine late transition metal alkyl complexes show activity in both C−H activation through σ-bond metathesis and olefin insertion. Herein, we show by analysis of their M−CH₃ ¹³C chemical shift tensors that these reactions involve a π(M−C) interaction in the horizontal plane of the complex for both d⁰ and d⁸ systems. While in the case of d⁰ systems the interaction of an empty metal d-orbital and a filled carbon p-orbital causes partial alkylidene character of the M−C bond, the corresponding metal d-orbital is filled in d⁸ systems, thus generating a filled π*(M−C) orbital that increases the anionic character of the methyl group. This entails fundamentally different reaction mechanisms for d⁰ and d⁸ systems, which are reflected in the structures of the transition states: While d⁰ olefin insertion can be viewed as a [2+2] cycloaddition reaction, d⁸ olefin insertion rather resembles methyl group migration onto a positively polarized olefin, thus explaining the observed differences in regioselectivity. These findings are translated to σ-bond metathesis, a reaction which is isolobal to olefin insertion for both early and late transition metals.     

Binding of Scandium Ions to Metalloporphyrin–Flavin Complexes for Long‐Lived Charge Separation

A porphyrin–flavin‐linked dyad and its zinc and palladium complexes (MPor?Fl: 2 ?M, M=2 H, Zn, and Pd) were newly synthesized and the X‐ray crystal structure of 2 ?Pd was determined. The photodynamics of 2 ?M were examined by femto‐ and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2 ?H₂ occurred from the singlet excited state of the porphyrin moiety (H₂Por) to the flavin (Fl) moiety to produce the singlet charge‐separated (CS) state ¹(H₂Por^.+?Fl^.?), which decayed through back ET (BET) to form ³[H₂Por]*?Fl with rate constants of 1.2×10¹⁰ and 1.2×10⁹ s^?1, respectively. Similarly, photoinduced ET in 2 ?Pd afforded the singlet CS state, which decayed through BET to form ³[PdPor]*?Fl with rate constants of 2.1×10¹¹ and 6.0×10¹⁰ s^?1, respectively. The rate constant of photoinduced ET and BET of 2 ?M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc³⁺ ions bind to the flavin moiety to form the Fl?Sc³⁺ and Fl?(Sc³⁺)₂ complexes with binding constants of K₁=2.2×10⁵ M ^?1 and K₂=1.8×10³ M ^?1, respectively. Other metal ions, such as Y³⁺, Zn²⁺, and Mg²⁺, form only 1:1 complexes with flavin. In contrast to 2 ?M and the 1:1 complexes with metal ions, which afforded the short‐lived singlet CS state, photoinduced ET in 2 ?Pd???Sc³⁺ complexes afforded the triplet CS state (³[PdPor^.+?Fl^.??(Sc³⁺)₂]), which exhibited a remarkably long lifetime of τ=110 ms (k_BET=9.1 s^?1).     

Studies on electrical properties of system La_(2-x)(Sr_(1-y)Ca_y)_xNiO_4

A new series of solid solutions of composition La_(2-x)(Sr_(2-y)Ca_y)_xNiO_4(0相似文献   

Substituent effects in second-row molecules: Basis set performance in calculations of normal valency phosphorus and sulfur compounds

Ab inito molecular orbital calculations of the phosphorus- and sulfur-containing series PH₂X, PH₃X⁺, SHX, and SH₂X⁺ (X = H, CH₃, NH₂, OH, F) have been carried out over a range of Gaussian basis sets and the results (optimized geometrical structures, relative energies, and electron distributions) critically compared. As in first-row molecules there are large discrepancies between substituent interaction energies at different basis set levels, particularly in electron-rich molecules; use of basis sets lower than the supplemented 6-31G basis incurs the risk of obtaining substituent stabilizations with large errors, including the wrong sign. Only a small part of the discrepancies is accounted for by structural differences between the optimized geometries. Supplementation of low level basis sets by d functions frequently leads to exaggerated stabilization energies for π-donor substituents. Poor performance also results from the use of split valence basis sets in which the valence shell electron density is too heavily concentrated in diffuse component of the valence shell functions, again likely to occur in electron-rich molecules. Isodesmic reaction energies are much less sensitive to basis set variation, but d function supplementation is necessary to achieve reliable results, suggesting a marginal valence role for d functions, not merely polarization of the bonding density. Optimized molecular geometries are relatively insensitive to basis set and electron population analysis data, for better-than-minimal bases, are uniform to an unexpected degree.     

First-principle investigation of magnetic coupling mechanism in hypothesized a-site-ordered perovskite YMn₃Sc₄O₁₂

We have systematically investigated the electronic and magnetic properties of hypothesized A‐site‐ordered perovskite YMn₃Sc₄O₁₂ using first‐principle calculation based on the density functional theory. Our calculated results predict that YMn₃Sc₄O₁₂ is both thermodynamically and mechanically stable and its ground state is antiferromagnetic insulator. The Mn³⁺ is in the high‐spin state. More importantly, by comparison to YMn₃Al₄O₁₂, we point out that the empty Sc 3d orbital provides the Mn? O? Sc? O? Mn superexchange interaction, which is similar to its isostructural perovskite CaCu₃Ti₄O₁₂, and enhances the antiferromagnetic interaction between Mn ions. From these calculations, we can clearly see that the empty 3d orbital plays an important role to realize superexchange interaction. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Giant Pressure‐Driven Lattice Collapse Coupled with Intermetallic Bonding and Spin‐State Transition in Manganese Chalcogenides

Materials with an abrupt volume collapse of more than 20 % during a pressure‐induced phase transition are rarely reported. In such an intriguing phenomenon, the lattice may be coupled with dramatic changes of orbital and/or the spin‐state of the transition metal. A combined in situ crystallography and electron spin‐state study to probe the mechanism of the pressure‐driven lattice collapse in MnS and MnSe is presented. Both materials exhibit a rocksalt‐to‐MnP phase transition under compression with ca. 22 % unit‐cell volume changes, which was found to be coupled with the Mn²⁺(d⁵) spin‐state transition from S=5/2 to S=1/2 and the formation of Mn?Mn intermetallic bonds as supported by the metallic transport behavior of their high‐pressure phases. Our results reveal the mutual relationship between pressure‐driven lattice collapse and the orbital/spin‐state of Mn²⁺ in manganese chalcogenides and also provide deeper insights toward the exploration of new metastable phases with exceptional functionalities.     

Activation of aromatic rings by early transition metal ions in the gas phase. Implications for the metal-catalyzed [2 + 2 + 2] cycloaddition of alkynes and nitriles

The reactions of a series of monocyclic and bicyclic arenes with early transition metal ions (Sc⁺, Y⁺, Nb⁺ and Ta⁺) and their oxides and dioxides were studied in a Fourier transform ion cyclotron resonance mass spectrometer. Ring cleavage of the nitrogen-containing heterocycles results in loss of HCN as the dominant pathway. Thermochemical considerations, secondary reactions and correlations with solution cyclotrimerization reactions indicate that the MC₄H₄⁺ product is a metallacyclopentadiene. Based on correspondence between the reactivities of a series of early metals with their valence electron counts, the reactivities of quinoline and isoquinoline and the decomposition behavior of the products, a metallacycloheptatriene intermediate is proposed for the heteroaromatic ring cleavage reaction. These results are compared to metal complexes in solution which catalyze the [2 + 2 + 2] cyclotrimerization of alkynes and nitriles.     

The structures of transition metal-transition metal alloys

A structure map using the average electron count and d orbital energy difference as indices is used to sort transition metal alloys of stoichiometry AB. The gross features of the map are mimicked by tight-binding calculations. The inclusion of s orbitals on the metal atoms appear to be important in the determination of alloy structure in some parts of the calculated map. The correct coloring of the elemental lattice as a function of electron count is reproduced by calculation (i.e., AuCd vs WC and CsCl vs CuTi). Two new stability fields for the WC and CuTi structures are predicted. The calculations fail to really distinguish bcc, fcc, and hcp derivative structures in the region of 6–8 d + s valence electrons per atom. In this part of the structure map the calculations appear to be sensitive to small geometrical changes.     

Contribution de la spectrometrie X à l'étude du manganèse dans les oxydes mixtes de structure spinelle: Analyse du spectre MnKβ et du seuil d'absorption K

Chemical shifts of Kβ_1,3 and Kβ₅ emission bands and X-ray absorption spectra near the K edge have been measured in several manganese spinel oxides with the metal in the formal oxidation states +2, +3, and +4. The position of line MnKβ_1,3 is determined mainly by the valence of manganese. The relative intensity of Kβ′ satellite with respect to the Kβ_1,3 line gives qualitative information about the presence of Mn(II) in mixed oxides. Mn(IV) oxides are characterized by a small chemical shift of the Kβ₅ band unlike Mn(II) and Mn(III) compounds. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE (Orsay, France). The chemical shifts ΔE (K absorption discontinuty) and ΔE_max (main peak) are correlated with the oxidation state of metal. Spectra of Mn³⁺ and Mn⁴⁺ ions in the octahedral environment are characterized by the splitting of 1s → 3d transitions (2 eV). In mixed oxides, the first Mn(II) 1s → 4s-4p transition is observed as a peak (or shoulder) located at 7 eV above the 1s → 3d transition. The study of the X-ray absorption fine structure in the near edge region can be used for qualitative solid-state analysis of mixed oxides such as NiMn₂O₄ or CuMn₂O₄.     

Relaxation Effect of Basis Orbitals on the Properties of Atomic and Molecular Hydrogen Systems

The effect of orbital relaxation on the properties of atomic and molecular hydrogen systems H, H ₂ ⁺ , H₂, H ₂ ⁻ , and H ₃ ⁺ calculated using the minimal basis set, the split valence shell basis set including the polarization function, and an extended basis set of grouped natural orbitals is considered. Inclusion of orbital relaxation in calculations results in a decreased total energy and more accurate energies of electron affinity. The strongest effect is produced on the calculated characteristics of the anions. The calculated activation energy of the radical reaction of hydrogen elimination. H₂ + H = H + H₂ depends strongly on the degree to which electron correlation is taken into account. Due to inclusion of orbital relaxation, the activation energy also approximates the experimental value, although to a lesser extent. The semiempirical PM3 method fails to adequately describe the transition state of this reaction, but this disadvantage is eliminated by using the exponent of the relaxed orbital of hydrogen.Original Russian Text Copyright © 2004 by A. I. Ermakov, A. E. Merkulov, A. A. Svechnikova, and V. V. Belousov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 979–985, November–December, 2004.