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Coordination spheres ionic radii

The formulated principals correlating crystal structure features with the X Nb(Ta) ratio do not take into account the impact of the second cation. Nevertheless, substitution of a second cation in compounds of similar types can change the character of the bonds within complex ions. Specifically, the decrease in the ionic radius of the second (outer-sphere) cation leads not only to a decrease in its coordination number but also to a decrease in the ionic bond component of the complex [277]. [Pg.116]

Most cations are strongly solvated, since their radii are small, and the free energy of solvation is approximately proportional to z2/r +, where ze0 is the cation charge in coulombs and r+ its ionic radius. The result of this is that even if the charge on the electrode is negative, there is usually little tendency for these cations to shed their water molecules and adsorb directly on the metal surface. Thus, the distance of closest approach of cations is determined by the radius of the inner solvent coordination sphere, and if the metal surface itself constitutes a plane, then the cation nuclei, at the distance of closest approach, will also constitute a plane termed the outer Helmholtz plane (OH P). [Pg.14]

Unlike the other alkaline earth and transition metal ions, essentially on account of its small ionic radius and consequent high electron density, Mg2+ tends to bind the smaller water molecules rather than bulkier ligands in the inner coordination sphere. Many Mg2+-binding sites in proteins have only 3, 4 or even less direct binding contacts to the protein, leaving several sites in the inner coordination sphere occupied by water, or in the phosphoryl transferases, by nucleoside di- or triphosphates. [Pg.166]

Type I spectra are associated with hydrated ionic compounds such as the MnCl2 4H2O and with many other compounds having a single octahedral coordination sphere. These spectra are sensitive to ionic charge and to radius of coordination sphere. [Pg.157]

Dissolution of alkali metal cations such as Cs+ results in short-range liquid order in water as a primary solvation shell of about eight water molecules is established about the metal cation. Lithium, however, exerts a much greater polarising power and is capable of organising a first- and second-coordination sphere of about 12 water molecules about itself, resulting in a much larger hydrated radius for the ion and hence decreased ionic mobility. [Pg.861]

With ethylenediamine complexes of the formula Ln(en)3X3 and Ln(en)4X3, where X = C1 , Br , NO, CIOJ have been characterized. IR data indicate that the tris and tetrakis complexes of the fighter lanthanides La-Sm, contain both ionic and coordinated nitrate groups. By contrast tetrakis complexes of heavier lanthanides, Eu-Yb contain ionic nitrate. This is possibly due to steric factors resulting from decreasing cationic radius that force the nitrate out of the coordination sphere of the lanthanides. A coordination number of 8 for tris complexes and a number of 9 for fighter lanthanide tetrakis complexes appears reasonable [234]. The thermodynamic parameters obtained show enthalpy stabilization for... [Pg.297]

AF Compounds. The stmctures of the dkali fluorides are all of the NaCl type however, the sensitivity to moisture for the K, Rb, and Cs compounds and their high-pressure phase transitions to the CsCl type show an increasing tendency to adopt the higher coordination number 8 with increasing ionic radius. In ternary compounds, it is mostly easier to adopt a more suitable coordination sphere of fluoride ligands Li+ may have tetrahedral coordination such as in scheelites LiMp4 and a few other compounds (see Section 3.2.13) but has normally CN 6. Na+ shows CN 6-8 with a certain favoring of CN 7. K+ clearly prefers CN 8, and Rb+ and Cs+ CN 10 to 12, in some cases up to 18. [Pg.1316]

Ion Ionic radius Coordination munber Typical geometry of inner-sphere complex First pA a of [M(H20) ] + , 2 22... [Pg.3162]

During recent years the application of the methods of x-ray and electron diffraction to the determination of the structure of molecules has permitted interatomic distances of a large number of bonds to be obtained and attempts have been made to find simple additive laws which will describe the observed data. In the case of ionic crystals the suggestion was made that each ion could be regarded as a small sphere, which just touch each other in the crystal. To each ion, therefore, there may be ascribed an ionic radius which is maintained by the ion in 1 crystals of a particular type, for example, in which the coordination number of the ion remains the same. For different coordination numbers of a particular ion, it is necessary to give different ionic radii. [Pg.189]


See other pages where Coordination spheres ionic radii is mentioned: [Pg.217]    [Pg.15]    [Pg.24]    [Pg.533]    [Pg.41]    [Pg.49]    [Pg.356]    [Pg.348]    [Pg.297]    [Pg.320]    [Pg.15]    [Pg.192]    [Pg.1014]    [Pg.34]    [Pg.71]    [Pg.95]    [Pg.346]    [Pg.247]    [Pg.360]    [Pg.186]    [Pg.433]    [Pg.110]    [Pg.11]    [Pg.70]    [Pg.357]    [Pg.71]    [Pg.95]    [Pg.66]    [Pg.4222]    [Pg.5325]    [Pg.6273]    [Pg.355]    [Pg.696]    [Pg.696]    [Pg.207]    [Pg.252]    [Pg.252]    [Pg.257]    [Pg.63]    [Pg.198]   
See also in sourсe #XX -- [ Pg.47 , Pg.53 ]




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Coordinate Sphere

Coordination sphere

Ionic coordinates

Ionic coordination

Ionic radius

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