Copper tellurium cluster

Tab. 13.2. High nuclearity copper tellurium clusters synthesized using silylated chalcogen reagents.

In all the copper tellurium cluster molecules, the tellurium atoms form poly-hedra with triangular faces. In the larger molecules, some of the tellurium atoms are located inside the polyhedral, whereas for the smaller cluster molecules the tellurium polyhedra can usually be derived from classical polyhedra (Figure 3.65). Those of the larger molecules often show unusual cage structures. The distances between the tellurium atoms are usually nonbonding, except for the Te—Te units in 59-62. 

Table 11 Copper tellurium clusters synthesized using sUylated chalcogen reagents.

Both alkyl and aryl tellurosilanes act as a good source of Rib and Te2 ligands, forming transition metal-tellurium clusters with cobalt(II) and copper(I) salts. The nuclearity of the cluster is determined primarily by the phosphine present, but also by... 

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. 

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. 

Those tellurium atoms that are located in the center of the cluster molecules tend to bond to a large number of copper atoms. In some compounds, the copper atoms themselves form polyhedra, described as Frank-Kasper polyhedra [62]. In these cases, the clusters consist of interpenetrating Frank-Kasper polyhedra, which are [34b, 63] well known from a number of intermetallic phases (e.g.. Laves phases). 

The ionic cluster compound 63 contains six TePh ligands, the tellurium atoms of which define an octahedron. In contrast to 64 (see below), all tellurolato ligands act as m2-bridges. There are two distinct coordination geometries around the copper, and two of the metal centers are located inside the cluster below Tc3 faces. The others are coordinated by three tellurium atoms above Te3 faces and are also each ligated by one phosphine ligand each. 

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

The crystals that are obtained from the cluster formation reactions are intensely colored. In fact, the intensity of the color increases when going from sulfur- to selenium- to tellurium-bridged compounds (see below), as might be expected for an increase in the covalent or (semi-) metallic binding properties. Small copper sulfide and selenide clusters form light red, orange, or purple crystals, but with increasing cluster size the color varies from dark red to reddish-black to (finally) black with a metallic sheen. The optical spectra of some copper selenide cluster compounds have been studied by means of solid-state UV-visible spectroscopy. 

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