Spectroscopy of transition metal compounds

Two excellent reviews1,2) on P.E. spectroscopy of transition metal compounds have appeared recently, and more general aspects of the technique are continuously reviewed3-6). Detailed exposition of fundamental principles of P.E. spectroscopy and its scope may be found in these and in the several books available on the subject7-12) this introduction will be restricted to particular general points of special relevance to the area covered. 

The development of electronic structure theories for metal complexes has always been closely linked with electron spectroscopy of transition metal compounds. We shall in the following describe both DFT and wave function methods that have been used in the study of excited states. We shall also discuss their application to the tetroxo systems. 

Excitation energies were computed with errors less than 0.2 eV in both cases. This was a higher accuracy than any of the earlier calculations on Ni and benzene had achieved. The CASPT2 method has during the last three years been applied to a large number of electronic spectra. Some of the earlier applications in organic chemistry have already been reviewed [13]. Here we discuss additional applications in organic systems but also the electronic spectroscopy of transition metal compounds, where the demands on the approach are different. 

The purpose of this chapter is to provide an overview of a rather wide array of experimental techniques that can tell us about the electronic structure of molecules. Some of these techniques, such as photoelectron (PE) spectroscopy, which is based on Einstein s photoelectric effect, are generally applied to gas-phase molecules. They can give high-resolution spectra, providing information about molecular vibrations and even, in a few cases, rotations. At the other end of the scale, UV/vis spectroscopy, particularly as applied to transition-metal complexes in solution, involves broad bands, and although it is an important and widely-used method, the information it gives is limited. Emission spectroscopy of transition-metal compounds has also become important. 

Postdoctoral research stay in Brookhaven National Laboratory (USA), work on Mossbauer spectroscopy of transition metal compounds... 

In 1964 Prof Ceilings was appointed professor of Inor nic Chemistry and Materials Science at the University of Twente. His main research interests were coordination chemistry and spectroscopy of transition metal compounds, corrosion and corrosion prevention, and catalysis. In 1991 he received the Cavallaro Medal of the European Federation Corrosion for his contributions to corrosion research. In 1992 he retired from his post at the University, but has remained active as supervisor of graduate students in the field of high temperature corrosion. 

During the last few years the versatility of ENDOR spectroscopy has been improved by a number of new techniques which make use either of special types of pumping fields (CP-ENDOR, PM-ENDOR), of more than one rf field (DOUBLE ENDOR, multiple quantum transitions, nuclear spin decoupling) or a different display of the spectrum (EI-EPR). In addition to these techniques, alternative methods have been developed (electron spin echo and electron spin echo ENDOR) which are able to supplement or to replace the ENDOR experiment under certain conditions. The utility of all these various advanced techniques, particularly in studies of transition metal compounds, has recently been demonstrated. 

Fig. 2. a) Required number of incoming x-ray photons to observe time-resolved EXAFS of transition metal compounds in H20 solution with a signal-to-noise ratio S/N = 1. No ligand or counterion contributions were included (see Fig. 1). Input parameters are /= 10%, %= 1 % (relative to the absorption edge jump of the selected element). The maxima of curves 2) in Fig. 1 for Fe and Ru correspond to the data points for these elements, b) Feasibility range for time-resolved x-ray absorption spectroscopy. The shaded region indicates the required x-ray dose per data point as a function of the fraction of activated species for the calculated EXAFS experiments on transition metal compounds shown in a). Curves (1) to (3) are extrapolated from experimental results (see section 3. for details) of time-resolved XANES.

Excitation spectroscopy in a molecular beam is a powerful technique leading to more insight into the excited state properties of transition metal compounds. 

The Application of Nuclear Quadrupole Resonance Spectroscopy to the Study of Transition Metal Compounds... 

This review is concerned with the latter area of interest and particularly in relation to the study of transition metal compounds. Those readers interested in the wider aspects of n. q. r. spectroscopy are referred to two excellent texts on the subject (9, 10) and a number of reviews (11—18) and compilations of data (19, 20) already published. 

Photoelectron spectra of Cd compounds have been reported see Photoelectron Spectroscopy of Transition Metal Systems), but discrepancies have been noted. X-ray photoelectron spectroscopy has been used in surface studies. Simmetry, bond length, and eqnUibrium constants see Equilibrium Constant) of Cd complexes have been determined through IR and Raman spectroscopy. Resonance Raman spectroscopy and Photoluminescence allow investigation of the optical properties of ultrathin CdS films. Electron diffraction studies have been reported. ... 

Bonding Energetics of OrganometaUic Compounds Electronic Structure of Main-group Compounds Electronic Structure of Solids Electronic Structure of Clusters Ligand Field Theory Spectra Molecular Orbital Theory Photoelectron Spectroscopy of Transition Metal Systems. 

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