Cu-0 distance

Figure 7.26 Plot of reduced with in-plane r(Cu-0) distance (From Rao Ganguli, 1995). Inset shows the variation of with AF (after Ohta et al, 1990).

Second, ab initio calculations were carried out to determine the Cu-0 distances, binding energies, and stretching force constants of hexaaquo Cu"+ clusters, Cun+ (H20)6, n = 1,2. The A, B, and C parameters in the last equa-... 

Figure S Variation of Tc with the apical Cu-0 distance in cuprate superconductors.

GHz). The spectral similarity between the type 2 Cu(II) in MCOs and in other mononuclear type 2 Cu(n) proteins is somewhat surprising since the coordination in the former is different than in the latter. While type 2 Cu(n) is most commonly characterized by a four-coordinate, tetragonally distorted square-planar ligand field (with, in some cases, some rhombic distortion also), the MCO type 1 Cu(II) is coordinated by two protein His residues and a solvent H2O only. The ligand field associated with this coordination is not directly obvious that is, among other uncertainties, whether the H2O is an equatorial or an axial ligand has not been estabhshed. In AO, the Cu-0 distance is 2.02-2.03 whereas in... 

An interesting example of at least partial destruction of resonance from Jahn-Teller distortion is given by bipyridinebis(hexafluoroacetylacetonato)copper(ll) (see Fig. 11.51 and accompanying discussion of the Jahn-Teller effect). As a result of this distortion, the two Cu—0 distances are not equivalent (197 vs. 230 pm) and presumably the tt bonding is not equivalent. Therefore one resonance form is favored over the other, and as a result there is an alternation of bond lengths throughout the ring (Fig. 12.48). 

When the Cu-0 bond is in the ionic limit, the Cu2+ ion will of course exhibit the behavior of a localized d9 ion. However, as the covalency increases, the Cu-0 distance decreases, the mixing with oxygen orbitals... 

When Ba, Sr, or Ca are substituted for La in La2Cu04, the Cu-0 distance steadily decreases. This happens despite the fact that Ba is much larger than La and thus causes a significant increase in the unit cell volume. It is apparently the inductive effect of the electropositive alkaline earth cation that causes increased covalency of Cu-0 bonds and therefore shorter Cu-0 bonds. (One could argue that A11 substitution causes decreased population of cr states and thus decreased Cu-0 distances. Although this is true, the net effect is still that all Cu-0 distances decrease.) The shorter Cu-0 bonds in turn results in increased Tc s. 

The reason that Tc s are highest in the Sr system is because Cu-0 distances become shortest in this system through a combination of geometric and inductive effects. The Tc s correlate very well with the Cu-0 distance (12). High pressure can be used to further decrease the Cu-0 distance, and Tc continues to increase (4). 

Table II lists the coordination of oxygen about the central copper atom in each of the high Tc ceramic superconductors and it lists typical Cu-0 distances. In the crystal structures, the coordination polyhedra are arranged so that the square planar configurations are perpendicular to the c-axis of the unit cell and the long axis of the pyramids and octahedra are parallel to it. Within planes of Cu-0 atoms, which are perpendicular to the unit...

Extended X-ray absorption fine structure (EXAFS) studies in aqueous solutions have shown that a water molecule in wild-type bovine S(i)D is 2.5 A (Cu-0 distance) from the metal 203). From H NMR studies the same distance is proposed (see later). Ligand field calculations have shown that the water molecule essentially does not affect the energy levels 89, 204). 

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