Metal-oxygen nearest distance

It seems that many workers would tend to equate die distanee (d) eorrespond-ing to the first RDF peak with the average distance between the center of the ion and the centers of the nearest water molecules, d=Tion + Twater Actually, Marcus presented a nice relationship between d, averaged over diffraction and simulation data, and the Pauling crystal radius in the form d=1.38 +1.102 rp. Notwithstanding this success, it is preferable to implicate not the water radius but instead the oxygen radius. This follows from the close correspondence between d and the metal-oxygen bond lengths in crystalline metal hydrates. ... 

Other Covalent Radii. In Cu20 and Ag20 each metal atom is equidistant from two nearest oxygen atoms, the interatomic distances corresponding to the radius values 1.18 and 1.39 A for Cu1 and Agl with coordination number two. In KAg(GN)2, in which each silver atom is similarly attached to two cyanide groups1), the effective radius of Agl is 1.36 A. It has been pointed out to us by Dr. Hoard that the work of Braekken2) indicates the presence of strings —Ag—G=N—Ag—G... 

Figure 9.5 EXAFS of Rh/AKO, catalysts after reduction at 200 °C (left) and 400 °C (right) top the magnitude of the Fourier transform of the measured EXAFS signal, bottom the back transformed EXAFS corresponding to distances from Rh atoms of between 0.8 and 3.2 nm. The lower Fourier transform contains a dominant contribution from Rh nearest neighbors at 0.27 nm and a minor contribution from oxygen neighbors in the metal-support interface. After correction for the Rh-O phase shift, the oxygen ions are at a distance of 0.27 nm (from Koningsberger et at. 119]).

Coordinative unsaturation arises from the fact that because of steric and electronic reasons, only a limited number of ligands or nearest neighbors can be within bonding distance of a metal atom or ion. In most transition metal oxides, the oxygen anions in the bulk form closed-packed layers and the metal cations occupy holes among the anions as schematically depicted in Fig. 2.1. In this picture, the oxide ion ligands appear to have saturated the coordination sphere of the bulk cation. 

Bidentate /3-diketonates usually have symmetric structure, and many crystal structures show sets of equal M—O, C—C and C—O bonds. Alkali metal enolate structures are symmetric as well as those for the Pd, Rh and A1 enolates. Few structures show unequal M—O distances these enolate complexes (M = Ge, Sn and Sb) are asymmetric as the metal atom is not located at equal distances from the nearest oxygen atoms . 

The oxides of iron are of broad interest because of their importance in such diverse fields as corrosion, catalysis, geochemistry and magnetism. Despite their different structures and metal oxidation states, the oxides of iron — FeO, Fe304, and a- and y-Fe203 - have in common a close-packed plane of oxygen anions in the (111) orientation in which the nearest-neighbor distances are rather similar (within 5%). The various phases differ in the distribution of Fe within the cation planes that lay between the oxygen planes. FeO is rocksalt, whereas... 

Average of various measurements and calculations [120]. internuclear distance between the metal ion and the next nearest oxygen atoms belonging to water molecules. 

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