Metals interactions between

Thus, in simple metals, interactions between dislocations rather than interactions between atoms, are most important. The hardnesses of metals depend on deformation hardening (dislocation interactions) rather than individual mobilities. The elastic resistance to shear plays a dominant role because it is directly involved with dislocation mobility. 

A metal can be considered as a fixed lattice of positive ions permeated by a gas of free electrons. Positive ions are the atomic cores, while the electrons are the valence electrons. For example, copper has a configuration (electronic structure) ls22s22p63s23p63dl04sl (superscripts designate number of electrons in the orbit) with one valence electron (4s). The atomic core of Cu+ is the configuration given above, less the one valence electron 4s1. The free electrons form an electron gas in the metal and move nearly freely through the volume of the metal. Each metal atom contributes its valence electrons to the electron gas in the metal. Interactions between the free electrons and the metal ions makes a large contribution to the metallic bond. 

Grey selenium (mp 494 K, metallic) is the stable form. It may be obtained crystalline from hot solutions of Se in aniline or from the melt. The structure, which has no sulfur analogue, contains infinite, spiral chains of selenium atoms. Although there are fairly strong single bonds between adjacent atoms in each chain, there is evidently weak metallic interaction between the neighboring atoms of different chains. Selenium is not comparable with most true metals in its electrical conductivity in... 

Fig. 6.35. Schematic energy-level diagram for the 3d orbitals in C09S8 showing a conduction band formed through metal-metal interactions between tetrahedral-site cobalt atoms [ct M(T)] and metal-sulfur-metal interactions to octahedral-site cobalt atoms [ct M(0)] (after Prewitt and Rajamani, 1974 reproduced with the publisher s permission).

Class la. We can envisage systems of bonded metal atoms which are then cross-linked by ligands X, there being no metal-metal interactions between the different sub-units. Examples include Gd2Cl3, Ta2S, and Ta S further examples are likely to emerge from studies of sub-halides, sub-chalconides, etc. 

The model potential is a function of the deviation (x-Aq) from the reference distance Xq, which is the equilibrium value when a is zero. The quadratic and cubic force constants /2 (positive) and (negative) are taken as the same for all molecules in a related series, whereas a is a perturbation expressing steric and electronic differences in ligand-metal interactions between related molecules (dotted line in Figure 5.16). The perturbation a affects AE 2md shifts the equilibrium distance to Xe = Xo + Aaq. In linear approximation the relationship is... 

Scheme 10.9 Discrete stacking of two planar metal complexes 26 within the pillared cage 27 causing metal-metal interactions between the guests...

There are numerous types of short-range interactions between adsorbed ions such as exchange-correlation effects, an overlap of their electronic cores, mutual polari2ation, interaction via the electrons of the metal, interaction between their solvation shells (which may partially be retained in the adsorbed state), changing of the local structure of the compact layer, and so on. All these forces decay rapidly with ion-ion distances exceeding the molecular scale, and the electrostatic contribution becomes dominant. A crucially important feature of this long-range contribution is a surprisin y slow decay as a function of R,... 

Ionic and covalent materials can combine in any group of valence compounds forming a class centered on simple or complex phases with four electrons per atom. Valence compounds with three and five electrons per atom are the nearest nel bors. In each of these subgroups we find that an increase in the atomic weight tends to increase the metallic interaction between the atoms and to alter the structure, However, most of the valence compounds are substances with mixed (ionic-covalent) bonds and with a gap in the electron energy spectrum, i.e., they are semiconductors. 

Figure 1. Ring-metal interaction between the HOMO e tt-MOs of two cyclopentadienyl anions and an e g d-orbital of the central metal.

Analogous ring-metal interaction between the e2uH0M0s of two... 

The widely applied Nieboer and Richardson (1980) tabulation of these metal ions classes is summarized in Table 1.1. The general trend in bond stability of the class (a) metal ions with various ligand donor atoms is O > N > S and that for class (b) metal ions is S>N>0 (Nieboer and Richardson 1980). Borderline metal ions are more complex, having binding tendencies intermediate between class (a) and (b) metals. Interactions between the hard class (a) metal ions and ligands tend to be ionic in... 

In a p-TcClj chain, two orientations of the Tc=Tc bonds in the [Tc Clg] unit are observed the Tc=Tc bonds of two adjacent [Tc Clg] units are either parallel or perpendicular (Figure 7.31), and the orientation of the Tc=Tc bonds changes every two [Tc Clg] units. The distances between Tc=Tc bonds of parallel (3.425(2) A) and perpendicular [Tc Clg] units (3.744(2) A) preclude any metal-metal interaction between adjacent units. In a-TcClj, only one orientation of the Tc=Tc bonds is observed, and the Tc=Tc vectors of adjacent units are parallel. The distances between Tc atoms of the adjacent units (3.417(2) A) also preclude any metal-metal interaction. 

Interestingly, the intermediate that results from the concerted transmetalation (CT-2) features a relatively short Pd-Zn distance (2.710 A), which suggests the existence of a metal-metal interaction between the electron rich Pd center and the fairly positive... 

A Pd6 L2 3 caging ligand 552 encapsulates planar platinum, palladium, and coppeifll) acety-lacetonates by Scheme 4.48 to give host-guest 1 2 cage complexes in quantitative yields [47]. The metal-metal interactions between their efficiently stacked guest molecules have been studied in solution using UV-vis and Pt NMR spectroscopies and in sohd state by X-ray difiiaction. 

The oligomerisation of dicyanoargentate(I) [and also dicyanoaurate(I)] ions in aqueous and methanolic solutions has lately been probed by UV-visible spectroscopy with results pointing to generation of metal-metal interactions between ions. Formation constants of 1.50 + 0.05 and 17.9 + 2.0 M have been obtained for [Ag(CN)2 ]2 and [Au(CN)2 ]2, respectively, at room temperature. ... 

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