Partial coordination numbers

Hap corresponds to the partial coordination number obtained by integrating the corresponding PCF first peak up to the first minimum. Results for previous simulations at from [26] and experiment from [88] compared to new simulation at and at the relaxed structure p ... 

All the grains of A that cannot be placed on the surface of C will be put into interstitial positions. The number Nac takes a hmiting value,. The partial coordination number z is estimated simply by the ratio of the area of grain C and the area of a large circle of grain A and thus ... 

The colors obtained depend primarily on the oxidation state and coordination number of the coloring ion (3). Table 1 Hsts the solution colors of several ions in glass. AH of these ions are transition metals some rare-earth ions show similar effects. The electronic transitions within the partially filled d andy shells of these ions are of such frequency that they fall in that narrow band of frequencies from 400 to 700 nm, which constitutes the visible spectmm (4). Hence, they are suitable for producing color (qv). 

The structure leads to a general formula for the micas namely, KXMY.1Oio(OH,r )2, with 2 < < 3, in which X represents cations of coordination number 6 (Al+3, Mg+, Fe++, Fe+3, Mn++, Mn+3, Ti+ Li+, etc.) and Y cations of coordination number 4 (Si+4, A1+3, etc.). The subscript n can have any value between 2 (hydrargillite layer) and 3 (complete octahedral layer). K+ can be partially replaced by Na+ and possibly to some extent by Ca++. This formula represents satisfactorily the.numerous recently published mica analyses almost without exception.6 The distribution of the various ions X and Y must be such as to give general agreement with the electrostatic valence rule. 

Instead, we believe the electronic structure changes are a collective effect of several distinct processes. For example, at surfaces the loss of the bulk symmetry will induce electronic states with different DOS compared to bulk. As the particle sizes are decreased, the contribution of these surface related states becomes more prominent. On the other hand, the decrease of the coordination number is expected to diminish the d-d and s-d hybridization and the crystal field splitting, therefore leading to narrowing of the valence d-band. At the same time, bond length contraction (i.e. a kind of reconstruction ), which was observed in small particles [89-92], should increase the overlap of the d-orbitals of the neighboring atoms, partially restoring the width of the d-band. 

The Li centers of the Lii2 unit are located on the edges of the P8 framework, whereas the Li centers of the Li60 core are each located over a face. This situation led to different coordination numbers (2 vs 4) for the two types of Li centers, implying much shorter Li-P bonds for the external ones (A ca. 0.2 A). That some of the 12 As centers of the anionic icosahedral partial structure in 6a can be replaced by other anions has only recently been demonstrated (32). Thus, 7a crystallizes in the monoclinic space group P2i/n and possesses a slightly distorted anionic icosahedral framework, which is identical to that observed for 6a, but two of the (AsR)2- units are replaced by iodide centers (Fig. 9). 

The coordination numbers of the Ln3+ ions in water are now well established from different experimental techniques (214-221). The lighter La3+-Nd3+ ions are predominantly nine-coordinate, Pm3+ Eu3+ exist in equilibria between nine- and eight-coordinate states and the heavier Gd3+-Lu3+ are predominantly eight-coordinate. The change in coordination number is also reflected in the absolute partial molar volumes, U°bs, of several Ln3+ ions determined in aqueous solutions (222,223). 

A distinctive feature of Ti4+ ions in tetrahedral coordination is the intense XANES peak at 4969 eV (39,97). The position and intensity of the pre-Ti K edge peaks can throw significant light on the coordination number and corresponding concentrations of surface Ti ions. The pre-edge intensity arising from the transition between the core level (in this case Is) to an unoccupied or a partially occupied level (3d, which is unoccupied, because Ti4+ is a d° system) is known... 

Tab. 2.4-1. Summary of alkali metal (M) amalgams containing anionic" mercury clusters, extended mercury partial structures and/or high coordination number polyhedra.

KyHg3i, which is not too far from K2Hg7 in chemical composition, is better characterized by an interpenetrating complex arrangement of K-centered high coordination number polyhedra [d(Hg-Hg) > 300 pm, Figure 2.4-8(c)] than by its mercury partial structure alone [4], thus leading into the essential aspects of Section 2.4.2.5. 

As a consequence the coordination number (or ligancy) of a central atom which is easily obtained by enumerating the neighbours (and which, of course, has an important role in the description of the crystal structure and of its geometrical characteristics), very often is not clearly and immediately related to the bonding mechanism of the intermetallic phase. In other words, there are many cases in which the enumeration procedure alone gives only a very partial representation of the bonding. Moreover, there are numerous cases where the criteria for the enumeration... 

The tetraallylic complexes of thorium and uranium can be isolated as red sohds and are stable to 0° and — 20°C, respectively, whereas the uranium homoalkyls defy isolation at temperatures as low as — 80°C. The greater stability of the thorium complex has been attributed partially to the great instability of Th(III) as compared with U(III) (96). The tc mode of bonding and the resultant increase in coordination number to eight of the allyl complexes significantly increases their thermal stability relative to the uranium homoalkyls. 

There have been many attempts to describe the process of mixing and solubility of polymer molecules in thermodynamic terms. By assuming that the sizes of polymer segments are similar to those of solvent molecules, Flory and Huggins derived an expression for the partial molar Gibbs free energy of dilution that included the dimensionless Flory Higgins interaction parameter X = ZAH/RT, where Z is the lattice coordination number. It is now... 

---