Transition metal complexes experimental techniques

In the following sections the effect of pressure on different types of electron-transfer processes is discussed systematically. Some of our work in this area was reviewed as part of a special symposium devoted to the complementarity of various experimental techniques in the study of electron-transfer reactions (124). Swaddle and Tregloan recently reviewed electrode reactions of metal complexes in solution at high pressure (125). The main emphasis in this section is on some of the most recent work that we have been involved in, dealing with long-distance electron-transfer processes involving cytochrome c. However, by way of introduction, a short discussion on the effect of pressure on self-exchange (symmetrical) and nonsymmetrical electron-transfer reactions between transition metal complexes that have been reported in the literature, is presented. 

Although studies of chemical reactions on transition-metal surfaces take place under very different conditions than chemical reactions catalyzed by discrete transition-metal complexes, several similarities are apparent, as indicated here. We are now in a periode of time where both experimental techniques and theoretical calculations are beginning to provide us with a picture of how chemical reactions on transition-metal surfaces take place - hopefully these studies will provoke others to try to develop discrete systems with similar properties, and thus show us that reac-... 

This technique has been used extensively as an experimental comparison for one or other of the types of theoretical molecular orbital calculations for organic and some nonmetallic inorganic compounds. However, for transition metal complexes and cluster compounds, their lower volatility presents some difficulties, and for the photoelectron spectra of the cluster alkyne complexes that have been recorded a heated inlet probe has been used to overcome this problem. 

The primary objective of this paper is to illustrate by specific examples from our past and current research how electrical property measurements can be of value in deducing information regarding the solid-state electronic structure and in studying intermolecular orbital interactions in such transition metal complex systems. To facilitate this discussion, a brief description of electrical conductivity and some other electrical properties is included. For a more detailed account as well as for a description of the various experimental techniques which are used to determine these properties, the reader is referred to any of several excellent books on the subject (12,13). 

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. 

Photoelectron spectroscopy relates molecular orbital energies, e obtained from molecular orbital calculations to experimentally observed ionization potentials via Koopmans theorem which is usually found to be reasonably accurate for main group compounds using dependable theoretical techniques (transition metal complexes sometimes are problematic). Furthermore, there is not just one peak for a single molecular orbital. As shown In 6.14 each molecule, M, contains a set of... 

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