Copper interatomic distance

The copper-copper interatomic distance in rhodium-copper clusters is substantially longer than in metallic copper (2.62-2.63A vs. 2.556A) and closer to the value (2.64A) obtained for the rhodium-... 

From Figure 4.15 we obtain for the osmium-copper interatomic distance in the catalyst a value of 2.675 A, which is about 0.05 A larger than the sum of the metallic radii of osmium and copper (36). The values for the osmium-osmium and copper-copper nearest neighbor distances in the catalyst, which are not shown in the figure, are 2.680 A and 2.550 A, respectively. The uncertainty is estimated to be 0.01-0.02 A in the determination of these interatomic distances (19,32). 

There are 2.56 d orbitals available for bond formation. To form 5.78 bonds these would hybridize with the s orbital and 2.22 of the less stable p orbitals. In copper, with one electron more than nickel, there is available an additional 0.39 electron after the hole in the atomic d orbitals is filled. This might take part in bond formation, with use of additional Ap orbital. However, the increase in interatomic distance from nickel to copper suggests that it forms part of an unshared pair with part of the bonding electrons, thus decreasing the effective number of bonds. 

The interatomic distances found are V—S = 2.186 0.040 A and Cu—S — 2.285 i 0.014 A. The Cu—S distance is somewhat smaller than the sum of the tetrahedral radii2) for sulfur and univalent copper, 2.39 A. As in the case of chalcopyrite, this probably indicates that the valence states are not well defined as CuIiVvSi, but fluctuate, the copper resonating between cuprous and cupric states and the vanadium between quinquivalent and lower states. 

Because of- the similarity in the backscattering properties of platinum and iridium, we were not able to distinguish between neighboring platinum and iridium atoms in the analysis of the EXAFS associated with either component of platinum-iridium alloys or clusters. In this respect, the situation is very different from that for systems like ruthenium-copper, osmium-copper, or rhodium-copper. Therefore, we concentrated on the determination of interatomic distances. To obtain accurate values of interatomic distances, it is necessary to have precise information on phase shifts. For the platinum-iridium system, there is no problem in this regard, since the phase shifts of platinum and iridium are not very different. Hence the uncertainty in the phase shift of a platinum-iridium atom pair is very small. 

Bipositive copper often forms four strong bonds directed toward the comers of a square. The observed interatomic distances correspond to the radius 1.28 A, about 0.08 A larger than for square-ligated nickel (II) the increase is to be attributed to the presence of the extra elec-... 

The Jahn-Teller effect enhances the structural diversity of Cu(II) compounds [68], Most of the octahedral complexes of Cu2+, for example, show elongated tetragonally distorted geometry. Crystalline cupric fluoride and cupric chloride both have four shorter and two longer copper-halogen interatomic distances, 1.93 vs. 2.27 A and 2.30 vs. 2.95 A, respectively [69],... 

Table 17-H-2 Interatomic Distances in Some Copper(II) Coordination Polyhedra...

Structure type ErsCuPbaSen (Gulay et al., 2006i) (Figure 98, Table 48). SG Cmcm, Z = 4, fl = 0.40710, h = 1.3480, c = 3.8092 run. The erbium and copper atoms are located in distorted octabedra and tetrahedra, respectively. The shortest interatomic distances among these coordination spheres are d(Er-Se) = 0.2795 nm and d(Cu-Se) = 0.240 nm. The selenium atoms create mono- and bicapped trigonal prismatic arrangements around the Pbl and Pb2 atoms, respectively, and the shortest Pb-Se distance is 0.2877 nm. The Sel and Se6 atoms are located in octahedra... 

The amplitude function A,(Af) is derived from the values of the maxima and minima of the function K x,(/0. For values of K other than those corresponding to maxima and minima, values of A, (/0 are obtained by interpolation. The values of the interatomic distance for metallic osmium and copper are 2.705 and 2.556 A, respectively. The value of 2.705 A for metallic osmium, which has the hexagonal close-packed structure, is the average of the interatomic distance (2.735 A) in a hexagonal layer and the distance of... 

Plots of the function K xUO vs. K at 100°K for the extended fine structure beyond the osmium edge for pure metallic osmium, and for the osmium-copper clusters in the catalyst containing 2 wt% Os and 0.66 wt% Cu, are shown in the left-hand sections of Figure 4.13. The associated Fourier transforms of the functions are shown in the right-hand sections of the figure. As previously noted, the Fourier transform yields the function n(R), the peaks of which are displaced from the true interatomic distances because of the phase shifts. Similar plots for the extended fine structure beyond the copper K edge for pure metallic copper and for the osmium-copper catalyst are given in our 1981 paper (32). 

When temperature is lowered, the band gaps usually increase [15]. There again, a few materials like lead sulphides or some copper halides are exceptions with a band gap increasing with temperature [96]. A quantitative analysis of the temperature dependence of the energy gaps must consider the electron-phonon interaction, which is the predominant contribution, and the thermal expansion effect. The effect of thermal expansion can be understood intuitively on the basis of the decrease of the interatomic distances when the temperature is decreased. A quantitative analysis of the electron-phonon contributions is more difficult, and most calculations have been performed for direct band-gap structures [75], Multi-parameter calculations of the temperature dependence of band gaps in semiconductors can be found in [81],... 

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