Selenium copper clusters

Zeolite channels have provided sites for silver [555, 556], silicon [557], and selenium [558, 559] clusters copper clusters have been generated between the layers of montmorillonite [560] and copper, platinum, and palladium clusters were formed in silicon dioxide matrices [561]. 

Selenium-Bridged Copper Clusters The reactions yielding all PR2R -coated selenium-bridged copper clusters that have been isolated and structurally characterized to date, in order of increasing cluster size, are summarized in Scheme 3.4. 

Scheme 3.4 Survey of the synthesis of selenium-bridged copper clusters protected by terminal phosphine ligands.

In the case of selenium-bridged copper clusters, it was found that there is a structural transition from molecular spherical structures towards cutouts of the bulk structure when the clusters reach 70 copper atoms. An analogous structural transformation has not yet been found in the case of sulfur-bridged silver clusters. For etample, the dication [Ag7oS2o(SPh)28(dppm)2o] in 94 shows a sheD-like sulfur substructure that consists of an inner Sg and an outer S40 polyhedron (Figure 3.73). 

Optical Spectra of Selenium-Bridged and Tellurium-Bridged Copper Clusters... 

Fig. 13.10. A projection of the copper-selenium core in the cluster [Cu52Se26(PPh3)i6] 13 [41].

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]. 

The largest copper selenide clusters isolated to date possess 140 or 146 copper atoms with 70 or 73 selenium ligands, respectively. The molecular stmctures of 34, 36 [23], and 37 are shown in Figure 3.52. 

---