Tellurium-Bridged Copper Clusters

All of the Cu—Te cluster compounds that have been synthesized and stmcturally characterized to date, using single-crystal XRD analysis, are summarized in Table 3.1. 

The species can be subdivided into four main groups, three of which consist of stoichiometric compositions [Cu2 Te (TeR)2x(PR2R )m] that differ in the nature of their tellurium ligands, while the fourth group represents the mixed-valence clusters. 

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 

CuOAc + nBuTe(SiMe3)2 CuCl + nBuTe(SlMe3)2 

Only with Te ligands With additional Te-Te bridges With additional TeR ligands  

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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. 

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. 

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