Step-cubane tetramer

In contrast to S, Se and Te form stable tetrachlorides, made by direct combination of the elements. At 298 K, both tetrachlorides are solids (SeC, colourless, subl. 469 K TeCl4, yellow, mp 497 K, bp 653 K) which contain tetrameric units, depicted in Figure 16.14c for SeCl4. The E—Cl (E = Se or Te) bonds within the cubane core are significantly longer than the terminal E-Cl bonds e.g. Te—Cl = 293 (core) and 231 (terminal) pm. Thus, the structure may also be described in terms of [ECls] and Cl ions. Stepwise removal of [ECls] from the tetramers E4CI16 (E = Se, Te) occurs in the presence of chloride ion in non-polar solvents, e.g. for the first step ... 

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