Clusters copper telluride

Unlike the copper telluride clusters, it has not yet proven possible to generate large silver telluride cluster complexes using a combination of R3P, Ag-X and Te(SiMe3)2. This suggests that the phosphine ligands are unable to kinetically... 

The copper atoms in the vast majority of the clusters can be assigned a formal charge of +1, while the chalcogen ligands are formally viewed as E or RE groups. Some of the selenium-bridged species, however - and nearly all copper telluride clusters - form nonstoichiometric compounds that display mixed valence metal centers in the formal oxidation states 0 and +I or +I and +11. These observations correlate with those made for the binary phases CU2S, Cu2 xSe, and Cu2- Te [38-40]. 

According to the general reaction pathway shown in Schemes 3.8 and 3.9, the syntheses of ligand-stabilized copper telluride clusters have mainly been achieved in one of three different ways [11, 16, 19, 20, 24, 25, 31, 61]. 

In the case of copper telluride clusters, the turning point in size has not yet been reached where the whole core structures display bulk structure characteristics, as seen for the copper selenide species. Nevertheless, the tellurium frameworks in the largest cluster compounds, 85-87 display hexagonal structure properties. Powder... 

Table 3.1 Classification of copper telluride clusters into stoichiometric or mixed valence, according to the types of tellurium ligand. 

Figure 3.66 Molecular structures of stoichiometric copper telluride clusters [CufiTejlPCyPhzls] (54), [CugTe4(PPh3)7] (55), [Cun2Te6(PPh3)s] (56). [Cui6Teg(PPhnPr2)io]...

In the following section, all cluster structures will be briefly described and discussed according to the division into four groups indicated in Table 3.1. The molecular structures of the stoichiometric copper telluride clusters 54-58 are shown in Figure 3.66. 

Some reactions of copper(I) chloride or copper(I) acetate lead to the formation of copper telluride clusters that contain Te-Te bridges (59-62 see Figure 3.67). 

Figure 5.15 The UV-visible solid-state absorption spectra (mull in nujol) of the mixed-valence copper telluride clusters [Cui6Te9(PPh3)g] (7), [Cu23Tei3(PPh3)io] (8), and [Cu44Te23(PPhnPr2)i5] (9).

Scheme 3-27. Formation of copper telluride clusters from CuQ.

This cluster represents the only example of a copper-telluride-tellurolate cluster yet isolated with a distinct structural relationship with its silver analog. 

Ten /13-TePh ligands adopt an unsymmetrical pattern of one shorter , one longer and one intermediate Cu-Te bonding distances. These distances (2.552(3)-2.708(3) A) are, expectedly, shorter than their Ag-Te counterparts, and reflect the difference between the ionic radii of the two metals.This contraction of the metal-tellurium bonding distances is reflected in the overall size of the cluster frame. Thus, for comparison, the Te4 - Te7 distance is 12.29 A in 5 and 12.95 A in 3a similarly the telluride ligands Tel5-- Tel6 are 7.72 A apart in the copper complex whereas they are separated by 8.81 A in the silver cluster 3a. 

Scheme 3.9 Reaction pathways for the formation of larger telluride-tellurolato-bridged copper clusters, starting from cluster precursors.

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