The Transition Metal Ion Chemistry

The Transition Metal Ion Chemistry of Linked Maerocyclic Ligands Leonard F. Lindoy... 

THE TRANSITION METAL ION CHEMISTRY OF LINKED MACROCYCLIC LIGANDS... 

The colour of the transition metal ions, which is one of their major characteristics, arises directly from the interaction between the outer orbital electrons of the transition metal and the electric field created by the presence of the co-ordinating ligands. The theory of this is called ligand field theory, and is well covered in most basic textbooks on inorganic chemistry (e.g., Cotton and Wilkinson, 1976). Ligand field theory is an extremely powerful tool, which... 

Clearly then, in glasses coloured by metal ions, the co-ordination chemistry of the transition metal ion has a major influence on the colour. The other major influence is the oxidation state of the metal ion, since variable valency is another characteristic of the transition metals. All other things being equal, for example, iron in the Fe11 form will give a pale blue colour, whereas Fem gives... 

Octacoordination is now recognized to be common for many lanthanide and actinide complexes. Among the < -transition metal ions, however octacoordination is less frequent. The d, d, d and d configurations are known to produce eight coordinated complexes (97). In an excellent review Lvppard (92) surveyed the chemistry of the octa coordinated complexes, especially stereochemical and bonding aspects, and included most of the published material upto 1967. 

The volume of activation which can provide very valuable information concerning the reaction mechanism is obtained by high-pressure pulse radiolysis (for a review in the area of transition metal ion chemistry, see van Eldik and Meyerstein 2000). 

Over the past several years, the area of gas-phase transition metal ion chemistry has been gaining increasing attention from the scientific community [1-16]. Its appeal is manifold first, it has broad implications to a spectrum of other areas such as atmospheric chemistry, corrosion chemistry, solution organometallic chemistry, and surface chemistry secondly, an arsenal of gas phase techniques are available to study the thermochemistry, kinetics, and mechanisms of these "unusual" species in the absence of such complications as solvent and ligand... 

Chapter 5 summarizes the crystal field spectra of transition metal ions in common rock-forming minerals and important structure-types that may occur in the Earth s interior. Peak positions and crystal field parameters for the cations in several mineral groups are tabulated. The spectra of ferromagnesian silicates are described in detail and correlated with the symmetries and distortions of the Fe2+ coordination environments in the crystal structures. Estimates are made of the CFSE s provided by each coordination site accommodating the Fe2+ ions. Crystal field splitting parameters and stabilization energies for each of the transition metal ions, which are derived from visible to near-infrared spectra of oxides and silicates, are also tabulated. The CFSE data are used in later chapters to explain the crystal chemistry, thermodynamic properties and geochemical distributions of the first-series transition elements. 

In this, my third contribution, I apply freeon dynamics to problems of interest in chemistry and physics and compare with the results obtained by the spin paradigm. In particular I will apply freeon dynamics to the following "spin phenomena" i) spin exchange, ii) spin superexchange, iii) spin polarization, iii) spin density, iv) high-and low-spin states of the transition-metal ions, v) the periodic table, vi) ferromagnetism, vii) spin waves and viii) high-Tc superconductivity. 

From the examples above, it is clear that oxidation reactions using redox-active molecular sieves is an active area of research for the synthesis of fine chemicals and intermediates. The novel chemistry is possible because of the location of the transition metal ions at specific crystallographic sites in the framework and also the pore structure of microporous materials. 

Important contributions to the area of defect chemistry of the acceptor-doped Lnj.xAxBOs, perovskites, where B is selected from Cr, Mn, Fe or Co, have been made by a number of investigators. Particular reference is made to reviews provided by Anderson [159,160] and Mizusaki [161]. The substitution of divalent alkaline-earth ions on the A-site increases the concentration of oxygen vacancies. Temperature and oxygen partial pressure determine whether charge compensation occurs by an increased valency of the transition metal ion at the B-site or by the formation of ionized oxygen vacancies. Thermogravimetric studies have indicated that in, for example, LaCrOs, YCrOs and LaMnOs the... 

In anaerobic soils, the individual chemistry of the ions is more distinctive. The transition metal ions in the middle of each period of the periodic table—chromium, manganese, iron, nickel, cobalt, and copper—can reduce to lower oxidation states, while the end members—scandium, titanium, and zinc—have only one oxidation state. The lower oxidation states are more water soluble but still tend to precipitate as carbonates and sulfides, or associate with organic matter, thus reducing their movement but increasing then plant availability. 

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