Transition metals electron paramagnetic resonance

Pilbrow JR. 1990. Transition ion electron paramagnetic resonance. Oxford Clarendon. Mabbs FE, CoUison DC. 1992. Electron paramagnetic resonance of transition metal compounds. Amsterdam Elsevier. 

F.E. Mabbs and D. Collison, Electron Paramagnetic Resonance of d Transition Metal Compounds, Elsevier, Amsterdam, 1992. 

The electron paramagnetic resonance spectrum of transition metal ions has been widely used to interpret the state of these ions in systems of catalytic interest. Major emphasis has been placed on supported chromia because of its catalytic importance in low-pressure ethylene polymerization and other commercial reactions. Earlier work on chromia-alumina catalysts has been reviewed by Poole and Maclver 146). On alumina it appears that the chromium is present in three general forms the S phase, which is isolated Cr3+ on the surface or in the lattice the 0 phase, which is clusters of Cr3+ and the y phase, which is isolated Cr5+ on the surface. The S and 0... 

Most stable ground-state molecules contain closed-shell electron configurations with a completely filled valence shell in which all molecular orbitals are doubly occupied or empty. Radicals, on the other hand, have an odd number of electrons and are therefore paramagnetic species. Electron paramagnetic resonance (EPR), sometimes called electron spin resonance (ESR), is a spectroscopic technique used to study species with one or more unpaired electrons, such as those found in free radicals, triplets (in the solid phase) and some inorganic complexes of transition-metal ions. 

Abragam, A. Bleaney, B. Electron Paramagnetic Resonance of Transition Metal Ions , Oxford University Press Oxford, 1970, pp. 133-216. 

Electron paramagnetic resonance (EPR) spectroscopy. This is also known as electron spin resonance (ESR) spectroscopy and is the electron analogue of NMR. In the case of EPR, however, the magnetic moment is derived from unpaired electrons in free radical species and transition metal ions. The paramagnetism of many transition metal oxidation states has already been mentioned as a drawback to the observation of their NMR spectra, but it is the raison d etre behind EPR the technique is thus limited, in the case of metals, to those which are paramagnetic or which have free radicals as ligands. 

Electron paramagnetic resonance (EPR) has been used extensively in studies of the mechanism of catalytic reactions. It has been used to identify free radicals and ion-radicals formed by chemisorbed species on catalytically active sites and to study the structure and distribution of paramagnetic catalytic sites such as those produced by transition metals or metal ions on a catalyst surface. EPR remains primarily aresearch tool for studying mechanisms of catalytic reactions. 

The conventional method for determining cation ordering and site populations within a crystal structure is by diffraction techniques using X-ray, electron and neutron sources. For determining site occupancies of transition metal ions, these methods have been supplemented by a variety of spectroscopic techniques involving measurements of Mossbauer, electron paramagnetic resonance (EPR or ESR), X-ray absorption (EXAFS and XANES), X-ray photoelectron (XPS), infrared and optical absorption spectra. 

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