Transition metal complexes, electron spin resonance

This article is an attempt to review possibilities in a quantum chemical treatment of open-shell systems. In order to cut down the extent of this review, we disregard some problems, especially those concerning macromolecules, polymerization reactions, and open-shell transition-metal complexes. Electron spin resonance is mentioned only briefly, because it has been a topic of many reviews. 

Electron Spin Resonance of Transition Metal Complexes B. A. Goodman and J. B. Raynor... 

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. 

Kuska, H. A., and M. T. Rogers Electron spin resonance studies and covalent bonding of cyanide and fluoride complexes of transition metals. J. Chem. Phys. 41, 3802 (1964). 

ELECTRON SPIN RESONANCE OF TRANSITION-METAL COMPLEXES... 

H. A. Kuska and M. T. Rogers, in Radical Ions (E. T. Kaiser and L. Kevan, eds.), Wiley, New York, 1968. Electron Spin Resonance of First Row Transition Metal Complex Ions. ... 

The technique of electron-spin resonance (e.s.r.), well known as an important tool for studying the structure of paramagnetic transition-metal complexes, has recently been used in the detection and study of a wide range of organic radicals, both stable and unstable, in fluids and solids. 

In the reduction of acetylene with molybdothiol and molybdoselenol complex catalysts, the effects of structural variation in ligands, variety of coordination-donor atom, kind of transition-metal ion, and other factors have been surveyed systematically. These factors have profound effects on the catalytic activity. The Mo complexes of cysteamine (or selenocysteamine), its N,N-dimethyl derivative, and its /3-dimethyl derivative give ethylene, ethane, and 1,3-butadiene, respectively, as the major product. The Co (I I) complexes of cysteine and cysteamine show higher catalytic activity than do the corresponding Mo complexes, and the order of the activity in the donor atom, namely S >Se 0 in the Co(II) complexes is consistent with that in the Mo complex systems. On the basis of electron spin resonance (ESR) features of these Mo complex catalysts, a relationship between their ESR characteristics and catalytic activities is discussed. 

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