Transition metal ions in electron

Several papers have appeared in press in the past three years using the B3LYP functional under PBC, as embodied in CRYSTAL98 [30]. The systems studied include several compounds of main group elements [40-57], compounds containing transition metal ions in formal electronic configuration d ° [58, 59], and compounds with one or more open shell transition metal ions in electronic configuration d " (n O) [60-64]. 

Gibson, J.F. Transition Metal Ions in Electron Spin Resonance, Vol. 1, R.O.C. Norman Ed. (The Chemical Society, London 1972). 

An atom or a molecule with the total spin of the electrons S = 1 is said to be in a triplet state. The multiplicity of such a state is (2.S +1)=3. Triplet systems occur in both excited and ground state molecules, in some compounds containing transition metal ions, in radical pair systems, and in some defects in solids. 

As with other hydroperoxides, hydroxyaLkyl hydroperoxides are decomposed by transition-metal ions in an electron-transfer process. This is tme even for those hydroxyaLkyl hydroperoxides that only exist in equiUbrium. For example, those hydroperoxides from cycHc ketones (R, R = alkylene) form an oxygen-centered radical initially which then undergoes ring-opening -scission forming an intermediate carboxyalkyl radical (124) ... 

Color from Transition-Metal Compounds and Impurities. The energy levels of the excited states of the unpaked electrons of transition-metal ions in crystals are controlled by the field of the surrounding cations or cationic groups. Erom a purely ionic point of view, this is explained by the electrostatic interactions of crystal field theory ligand field theory is a more advanced approach also incorporating molecular orbital concepts. 

Table 1-2. The electronic configurations of the transition-metal ions in the divalent and triva-lent states.

The chapter Electron Spin Resonance in Catalysis by Lunsford was prompted by the extensive activity in this field since the publication of an article on a similar subject in Volume 12 of this serial publication. This chapter is limited to paramagnetic species that are reasonably well defined by means of their spectra. It contains applications of ESR technique to the study of adsorbed atoms and molecules, and also to the evaluation of surface effects. The application of ESR to the determination of the state of transition metal ions in catalytic reactions is also discussed. 

Strong crystalline field Hso < H e < Hqf- In this approach, the crystalline field term dominates over both the spin-orbit and the electron-electron interactions. This applies to transition metal ions in some crystalline environments (see Section 6.4). 

In a transition metal chalcogenide or oxide, positive guests like Li occupy sites surrounded by negative chalcogen or oxygen ions, and distance themselves as far as possible from the positive transition metal ions. Since Li has a filled outer core of electrons (unlike the transition metal ions in many of the hosts), the geometry of the site is not important as long as the anions are distributed evenly around the site. Thus y" surrounded by four anions would prefer the anions to form a tetrahedron rather than a square. 

The focus of this paper is on the role electronic structure plays in determining the site preference and mobility of 3d transition-metal ions in an oxide and how these factors in turn affect the resistance of metastable 3d transition-metal oxides against transformation. This is a relevant topic to the Li rechargeable battery field because 3d transition-metal oxides are often used as positive electrode materials. 

We first note that an isolated atom with an odd number of electrons will necessarily have a magnetic moment. In this book we discuss mainly moments on impurity centres (donors) in semiconductors, which carry one electron, and also the d-shells of transitional-metal ions in compounds, which often carry several In the latter case coupling by Hund s rule will line up all the spins parallel to one another, unless prevented from doing so by crystal-field splitting. Hund s-rule coupling arises because, if a pair of electrons in different orbital states have an antisymmetrical orbital wave function, this wave function vanishes where r12=0 and so the positive contribution to the energy from the term e2/r12 is less than for the symmetrical state. The antisymmetrical orbital state implies a symmetrical spin state, and thus parallel spins and a spin triplet. The two-electron orbital functions of electrons in states with one-electron wave functions a(x) and b(x) are, to first order,... 

For later discussions it is important to consider what happens if one of the d-orbitals (eg or t2g) is not full (e.g. CoO with seven electrons per atom or TiCl3 with one). The d-orbital is now degenerate, and the orbital motion is no longer quenched. Consider the case of a transitional-metal ion in the d1 state. Suppose that the spins are parallel to the z-axis the spin-orbit coupling will separate the orbitals into functions of the forms... 

Such matters can be represented in a different way in terms of the d-electron configuration of transition metal ions in a molecular orbital scheme (Fig. 7.113). 

Electron transfer data for transition metal ions in glass and related media have been... 

Among electrode processes with at least one charge transfer step, several different types of reaction can be found. The simplest interfacial electrochemical reactions are the exchange of electrons across the electrochemical interface by flipping oxidation states of transition metal ions in the electrolyte adjacent to the electrode surface. The electrode in this case is merely the source or sink of electrons, uptaking electrons from the reduced species and releasing them to the oxidized redox species in solution. Examples of simple electron transfer reactions are... 

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