Metal cluster compounds colors

M = Ir, yellow). A similar effect is often observed in the colors of other types of tremsition metal derivatives, particularly organometallic compounds (237), but this effect is rarely as large as it is with metal cluster compounds. 

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. 

Polyatomic anions of tin can be prepared in solution, using alloys of tin with alkali metals which are remarkably soluble in liquid ammonia. The obtained colored solutions contain the cluster anion [Sng]4, 68a106. Upon treatment with a crown ether in ethylenediamine, crystalline compounds [Na(crypt)+]4[Sn9]4 could be prepared where crypt = N(CH2CH20CH2CH20CH2CH2)3N ... 

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