Structure Of Transition Metal Ions Research Articles

Near-Quantitative Predictions of the First-Shell Coordination Structure of Hydrated First-Row Transition Metal Ions Using K-Edge X-ray Absorption Near-Edge Spectroscopy.

The solvation structure of transition metal ions is important for applications in geochemistry, biochemistry, energy storage, and environmental chemistry. We study the X-ray absorption pre-edge and near-edge spectra at the K-edge of a nearly complete series of hydrated first-row transition metal ions with d orbital occupancy from d2 to d10. We optimize all of the structures at the density functional theory (DFT) level with explicit solvation and then compute the pre-edge X-ray absorption spectra with time-dependent DFT (TDDFT) and restricted active space second-order perturbation theory (RASPT2). TDDFT provides accurate results for spectra that are dominated by single excitations, while RASPT2 correctly distinguishes between singly and doubly excited states with quantitative accuracy compared with experiment. We analyze the pre-edge features for each metal ion to reveal the impact of the variations in d orbital occupancy on the first-shell coordination environment. We also report the lowest-energy ligand field d-d transitions using complete active space second-order perturbation theory.

Raman, EPR and structural studies of novel CuZrNb2O8 ceramic for LTCC applications

Abstract To determine the mechanism of microwave response in AZrNb2O8 (A: Mn, Zn, Mg, Co, et al.) wolframites, CuZrNb2O8 ceramic with low sintering temperature (920 °C) is successfully fabricated by solid-state reaction method. Meanwhile, its structural stability is synthetically evaluated, the vibration modes are also calibrated. Except for the extrinsic factor like sintering temperature, the condition of Jahn-Teller ion Cu2+ as intrinsic part is characterized for the first time in relation to the microwave dielectric properties of the system. In virtue of Raman and EPR spectra, it is predicted that the electronic structure of transition metal ions, as the less concerned factor, may be influential on the dielectric properties of ceramics at microwave range, especially in the structure with mixed ion occupancy. In addition, the CuZrNb2O8 ceramic is well matched with the silver electrode, which makes it a prospective candidate for temperature compensation material of LTCC (low-temperature co-fired ceramic) passive integration technology.

Probing the Valence Electronic Structure of Low-Spin Ferrous and Ferric Complexes Using 2p3d Resonant Inelastic X-ray Scattering (RIXS).

Understanding the detailed electronic structure of transition metal ions is essential in numerous areas of inorganic chemistry. In particular, the ability to map out the many particle d-d spectrum of a transition metal catalyst is key to understanding and predicting reactivity. However, from a practical perspective, there are often experimental limitations on the ability to determine the energetic ordering, and multiplicity of all the excited states. These limitations derive in part from parity and spin-selection rules, as well as from the limited energy range of many standard laboratory instruments. Herein, we demonstrate the ability of 2p3d resonant inelastic X-ray scattering (RIXS) to obtain detailed insights into the many particle spectrum of simple inorganic molecular iron complexes. The present study focuses on low-spin ferrous and ferric iron complexes, including [FeIII/II(tacn)2]3+/2+ and [FeIII/II(CN)6]3-/4-. This series thus allows us to assess the contribution of d-count and ligand donor type, by comparing the purely σ-donating tacn ligand to the π-accepting cyanide. In order to highlight the conceptual difference between RIXS and traditional optical spectroscopy, we compare first RIXS results with UV-vis and magnetic circular dichroism spectroscopy. We then highlight the ability of 2p3d RIXS to (1) separate d-d transitions from charge transfer transitions and (2) to determine the many particle d-d spectrum over a much wider energy range than is possible by optical spectroscopy. Our experimental results are correlated with semiempirical multiplet simulations and ab initio complete active space self-consistent field calculations in order to obtain detailed assignments of the excited states. These results show that Δ S = 1, and possibly Δ S = 2, transitions may be observed in 2p3d RIXS spectra. Hence, this methodology has great promise for future applications in all areas of transition metal inorganic chemistry.

Magnetic Chern Insulators in a monolayer of Transition Metal Trichalcogenides

A monolayer of transition metal trichalcogenides has received a lot of attention as potential two dimensional magnetic materials. The system has a honeycomb structure of transition metal ions, where both spin-orbit coupling and electron correlation effect play an important role. Here, motivated by these transition metal series with effective doping or mixed valence case, we propose the possible realization of magnetic Chern insulators at quarter filled honeycomb lattice. We show that the interplay of intrinsic spin-orbit coupling and electron correlation opens a wide region of ferromagnetic Chern insulating phases in between metals and normal insulators. Within the mean field approximation, we present the phase diagram of a quarter filled Kane-Mele Hubbard model and also discuss the effects of Rashba spin-orbit coupling and nearest neighbor interactions on it.

Electronic structure of transition metal ions in GaN and AlN: Comparing GGA+U with experiment

Electronic structure of Cr, Mn, Fe, and Co transition metal (TM) ions in GaN and AlN is studied within the Generalized Gradient Approximation augmented by the +U corrections, which are treated as free parameters. The main impact of U(N) is the opening of the band gap by shifting both valence and conduction band energies. The intracenter transitions between the gap states of TM impurities are weakly affected by U(N), but they are sensitive to U(TM) which directly act on d(TM) orbitals. The impact of U(TM) depends on both the level symmetry and its occupancy (i.e., on the charge state of the TM ions). Degeneracies of partially occupied multiplet levels are lifted, the effect being mainly driven by the +U correction and not by the Jahn-Teller mechanism. The role of the U-induced hybridization between TM and host states is elucidated.A comparison with experimental intracenter optical transition energies demonstrate that the best agreement is obtained for U ≈ 0 for Fe, and even negative U ≈ −1 eV for Mn. The linear response calculations give U(TM)≈3.5–4.0 eV, which leads to severe discrepancies of about 1 eV with experiment. Importantly, the results obtained with U(Fe) = U(Mn) = U(N) = 5 eV are very close to those obtained with hybrid functionals, but the discrepancies with experiment are even larger. Comparison of the results for GaN and AlN shows that relative energies of gap levels of a given TM ion in the two hosts, as well as their dependencies on U(TM), are the same to within ∼0.2 eV. The estimated valence band offset between GaN and AlN is about 0.5 eV, in agreement with experiment.

X-ray absorption study of the geometry structure of Co2+/Co3+ in ammonia solution

The investigation of the geometrical structure of transition metal ions in solution is mandatory to determine the role of transition metal ions in many chemical reactions. In this contribution, the local structure of Co2+/Co3+ in ammonia solution was investigated by X-ray absorption spectroscopy (XAS). We found that Co2+ ions are coordinated by six NH3 ligands arranged in a Jahn-Teller (JT) distorted octahedral (DT Oc) geometrical configuration with four long Co-Neq bonds (2.17 Å) and two short Co-Nax bonds (2.03 Å). At variance, Co3+ ions in [Co(NH3)6]3+ or [Co(NH3)5Cl]2+ clusters occur depending on the presence of activated carbons during the oxidation reaction process from Co2+ to Co3+. By means of full multiple-scattering theoretical (MXAN) analysis of the Co K-edge XANES (X-ray absorption near edge structure), we show that [Co(NH3)6]3+ is characterized by a regular octahedral (Re Oc) geometrical structure with a Co–N distance 1.91 Å long while [Co(NH3)5Cl]2+ by a distorted octahedral geometrical structure with four Co-Neq bonds (1.94 Å), a shorter Co-Nax bond (1.91 Å) and a Co–Cl bond (2.12 Å).

Magnetic interactions and optical spectral weights in Mott insulators with orbital degrees of freedom

AbstractWe outline a unified approach to magnetic and optical properties of Mott insulators at orbital degeneracy, which provides deep insight into the complex spin–orbital physics. It introduces partial sum rules for individual optical excitations which follow from the multiplet structure of transition metal ions. We show that the observed anisotropies and the temperature dependence of the optical spectral weights in LaVO3 and LaMnO3 follow from spin and orbital correlations and are well understood within this approach. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic Structure of Transition Metal Ions in Deintercalated and Reintercalated LiCo0.5Ni0.5 O 2

We studied the electronic structure of the transition metal ions in deintercalated and reintercalated . The experimental technique used in the study was Co 2p and Ni 2p X‐ray absorption spectroscopy. The shapes of the multiplet in the spectra are directly related to the ground state of the transition metal ions. The experimental results were analyzed using atomic multiplet plus crystal field calculations. The Co ions were in a trivalent low‐spin state in and remained mostly unaffected by Li deintercalation down to x = 0.20. The Ni ions were in a divalent high‐spin state in and not in the usually quoted trivalent state. The Ni ions were partially oxidized to a trivalent state upon Li deintercalation down to x = 0.50. Further Li deintercalation, down to x = 0.20, did not result in further oxidation of the Ni ions. The changes in the electronic structure of the Ni ions were reversible upon Li reintercalation. © 2000 The Electrochemical Society. All rights reserved.

Spectroscopy of transition metal ions in inorganic glasses

Transition metal (TM) ions have been used as colouring agents in the glass industry for a long time. Recently, great attention has been paid to the TM ion doped glasses for the development of new lasers or luminescence materials. The absorption spectra of TM ions in different kinds of glasses have been studied extensively, but little work has been done for fluorescence and relaxation spectra. In this paper emphasis is laid on analysing the influence of chemical bond characteristics of the base glass on the spectra and the site structure of transition metal ions in glasses. Recent experimental results about the luminescence characteristics of low valence ions (such as Ti 3+, Cr 3+, V 2+, Mn 2+, Cu +, Mo 3+) in glasses are also reported.

Electron spin-echo study on the hydration structure of transition metal ions on cation exchangers

Electron spin-echo modulation studies of paramagnetic transition metal ions, Cu 2+, Mn 2+ and Cr 3+, adsorbed on cation exchangers, SiO 2, TiO 2 and cross-linked polystyrenesulfonic acid, hydrated by D 2O have been carried out at 4.2 K for elucidating the hydration structure of cations on the exchangers. Analysis of the deuterium electron spin-echo modulation by D 2O coordinated to the metal ions shows that the hydration numbers are two, four and three for Cu 2+, Mn 2+ and Cr 3+, respectively. Comparison of these hydration numbers with those for the fully hydrated metal ions in aqueous solutions indicates that ion associations take place on the exchangers, at least at low temperatures. It is concluded that the adsorption of fully hydrated metal ions of the valency n and the hydration number m, M n+ (H 2O) m , onto the cation exchangers with the exchange groups Ex-O − is generally expressed by the reaction M n+ (H 2O) m + n(Ex−O −)⇋M n+ (H 2O) m ---(Ex−O) n ⇋M n+ (H 2O) m− n (Ex−O) n ⇋ M n+ (H 2O) m− n (Ex−O) n + nH 2O .

Oxygen - 17 superhyperfine structure of transition metal ions in MgO

EPR measurements of the oxygen-17 superhyperfine structure of Fe 3+ Cr 3+, Ni 3+ and Rh 2+ impurities in isotopically labeled single crystals of MgO have been made. In connection with the interpretation of the spectra of the Jahn-Teller ions Ni 3+ and Rh 2+, expressions are derived for the superhyperfine Hamiltonian for the 2E state in octahedral symmetry.

Electronic Structure of Transition Metal Ions in a Tetrahedral Lattice

Electronic Structure of Transition Metal Ions in a Tetrahedral Lattice