Valence states and coordination

The reactions of primary and secondary radicals with metal complexes, including bioinorganic compounds, are of the following types redox, addition and atom transfer. The products of the reactions include metal centers in unusual valency states and coordinated ligand-radicals ... 

To a large degree, the extensive development of phosphorus chemistry is due to the great variety of different valence states and coordination numbers that the element phosphorus exhibits. Until about twenty years ago, the chemistry of phosphorus compounds included mainly the well known pDI and valence states with their common coordination numbers of three, four, and five. In recent years, however, these ideas have changed dramatically and it is now known that phosphorus can form a variety of "low-coordinate" structures (7). These novel sterns include phosphorus in one- and two-coordinate and three-coordinate P environments, with (p-p)7C bonds to adjacent elements, including C, N, P, Si, B, etc. 

For a better understanding of the first steps of the reaction of NO over Cu-ZSM-5 and Fe-ZSM-5 zeolites the following measurements were performed (i) the products of the gas phase interactions were followed by MS, (ii) the valence state and coordination of transition metal ions in zeolites by ESR spectroscopy. Catalysts were prepared both by conventional and solid-state ion-exchange methods and pretreated in vacuum, in oxidative and in reductive atmosphere. The conventional ion-exchanged samples are more active in NO decomposition than the solid-state exchanged ones. Over the reduced catalysts the first step consists in N2O formation and the oxidation of Cu Cu (Fe Fe ) followed by N2O reduction to N2 (in these conditions O2... 

ESR spectroscopy is a powerfiil tool to monitor the valence state and coordination of cupric and iron ions in zeolites. After different pretreatment procedures (listed in Table 2) and/or NO adsorption spectra were recorded on a Brttker BER-420 spectrometer with a TE102 rectangular cavity - at both ambient temperatirre and 77 K. 

The Stabilization of Unusual Valence States and Coordination Numbers by Bulky Ligands... 

MUlet, J.M.M., Baca, M., Pigamo, A., Vilry, D., Ueda, W., and Dubois, J.L. Study of the valence state and coordination of antimony in MoVSbO catalysts determined by XANES and EXAFS. Appl Catal A Gen. 2003, 244, 359-370. 

ESR spectroscopic examination may be helpful to understand valence states and coordination of metal cations microscopically. 

K+ is generally used as the reversibly intercalating ion since it leads to insoluble compounds for all the forms. In the mixed-valence Prussian Blue compound, Fe is in the high-spin state and coordinated octahedrally with the N ends of the cyaiudes, whereas Fe is low-spin and octahedrally coordinated with the C ends of the... 

K EDGE ABSORPTION SPEGTRA. The absorption of x-rays in the vicinity of the K absorption edge of transition metals gives information on both oxidation state and coordination geometry of the central absorbing atom. The energy positions of various absorption features have been demonstrated to be correlated to the formal valence of V in an extensive series of oxides, vanadates and intermetallics (13"). 

In the mathematical theory of networks valence is defined as the number of links terminating at a node, and it was in this sense that the term was introduced into chemistry. However, chemists were later forced to distinguish between a chemical valence (bonding power) and a coordinative valence (number of bonds). They chose to keep the term valence for the chemical valence and introduced the term coordination number for the coordinative valence. This book follows the chemical convention. The term valence is always used in the sense of bonding power unless otherwise stated, and coordination number is used to indicate the number of bonds. 

Werner s terminology ami symbolism differed in small, relatively unimportant ways from that used today. For example. Wcroer referred lo oxidation -state as primary valence Waiipiviilcnc) and coordination number as secondary valence (Nehemulenz) Also, he wrote formulas as Co J A C1 . instead of [CoiNHjljCllClj... 

The size of an arsenic atom depends on its valence state and the number of surrounding atoms (its coordination number). When valence electrons are removed from an atom, the radius of the atom not only decreases because of the removal of the electrons, but also from the protons attracting the remaining electrons closer to the nucleus (Nebergall, Schmidt and Holtzclaw, 1976), 141. An increase in the number of surrounding atoms (coordination number) will deform the electron cloud of an ion and change its ionic radius (Faure, 1998), 91. Table 2.2 lists the radii in angstroms (A) for arsenic and its ions with their most common coordination numbers. 

Next, imagine that the promoted atom is one of many, all similarly activated by a static field of applied pressure. All atoms are in the same valence state and interact non-locally through quantum torque and the quantum-potential field, which becomes a function of all particle coordinates. This... 

Dimeric associations (75) are typical of some low oxidation state and coordinatively unsaturated complexes that spontaneously exhibit a tendency to completely fill the valence electronic shell around the metal. Dinuclear dihydride [(C5H4Me)2ZrH(/x-H)]2, for which the two metallocene-H units are joined by two Zr-H-Zr (two-electron-three-center bonds) are examples of this family. ... 

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