Transition metal and rare earth compounds are investigated intensively because of important questions concerning fundamental research problems. More recently also their enormous potential for the development of new materials for photophysical and photochemical applications has been explored. Thus, it is important to focus on a deeper understanding of the elctronic energies, transition prohabilities, intermolecular interactions, etc.. This task has been accomplished by leading researchers in the field. They present introductions into, but also detailed reviews of the current state of knowledge of three different subjects.
Transition metal and rare earth compounds are investigated intensively because of important questions concerning fundamental research problems. More recently also their enormous potential for the development of new materials for photophysical and photochemical applications has been explored. Thus, it is important to focus on a deeper understanding of the elctronic energies, transition prohabilities, intermolecular interactions, etc.. This task has been accomplished by leading researchers in the field. They present introductions into, but also detailed reviews of the current state of knowledge of three different subjects.
There exists a large literature on the spectroscopic properties of copper(II) com- 9 pounds. This is due to the simplicity of the d electron configuration, the wide variety of stereochemistries that copper(II) compounds can adopt, and the f- xional geometric behavior that they sometimes exhibit [1]. The electronic and geometric properties of a molecule are inexorably linked and this is especially true with six-coordinate copper(II) compounds which are subject to a Jahn-T- ler effect.However,the spectral-structural correlations that are sometimes d- wn must often be viewed with caution as the information contained in a typical solution UV-Vis absorption spectrum of a copper(II) compound is limited. Meaningful spectral-structural correlations can be obtained in a related series of compounds where detailed spectroscopic data is available. In the fol- 4– lowing sections two such series are examined; the six-coordinate CuF and 6 2+ Cu(H O) ions doped as impurities in single crystal hosts.Using low tempera- 2 6 ture polarized optical spectroscopy and electron paramagnetic resonance, a very detailed picture can be drawn about the geometry of these ions in both their ground and excited electronic states. We then compare the spectrosco- cally determined structural data with that obtained from X-ray diffraction or EXAFS measurements.
Transition metal and rare earth compounds are investigated intensively because of important questions concerning fundamental research problems. More recently also their enormous potential for the development of new materials for photophysical and photochemical applications has been explored. Thus, it is important to focus on a deeper understanding of the elctronic energies, transition prohabilities, intermolecular interactions, etc.. This task has been accomplished by leading researchers in the field. They present introductions into, but also detailed reviews of the current state of knowledge of three different subjects.
This book presents advances in the field of rare-earth (R) – transition metal (M) – boron compounds with extensive references. Since titanium and scandium do not form compounds with rare-earths, the Sc/Ti-M-B series are additionally presented. In each chapter the crystal structures, the complex physical properties as determined from neutron diffraction, magnetic measurements, resonance studies, transport properties and band structure calculations are critical analyzed. The models used in describing the experimental evidence are also presented. Tables with the main properties of the R-M-B compounds are given and representative data are illustrated in figures. In this way, the book provides state-of-the art knowledge and a valuable analysis of up-to-date results in the field. The technical applications, as permanent magnets, thermoelectric and magnetocaloric devices, hydrogen storage are also highlighted along with the authors insights into future directions in the field. The book is of interest for scientists involved in the development of the field as well as those working in the technical uses of rare-earth compounds.
The alloying characteristics of the rare earth elements with the transition metals undergo a radical change as the atomic number of the transition series increases - - transition elements in Groups IVa, Va, and VIa are immiscible with the rare earths, while elements of Groups VIIa, and VIIIa, VIIIb, and VIIIc form many compounds. Since this cannot be correlated with a size effect, a reasonable explanation for this behavior is a valency or electronegativity effect. Those binary systems forming compounds form 'Laves phases', which can exist in one of three related crystal structure types: MgCu2, MgZn2, or MgNi2. The specific Laves type crystal structure can be related to the average free electron concentration, a phenomenon which has been used to calculate electronic valency of the transition elements. A compilation of the known Laves-type phases occurring between rare earth elements and transition metals supports the hypothesis that the valency effect is operative. Forty-two additional rare earth-transition metal compounds previously unknown have been prepared and found to be consistent with the previously noted trend with but two exceptions. On the assumption that a critical electron/atom ratio determines which Laves-type structures are stable, the periodical grouping of the Laves-type species of the rare earth-transition metal compounds indicates a slight but regular increase in valency as the atomic number of the rare earth increases. Ternary alloys prepared between the Laves phases of different structure types substantiate the observed valency trend.
