Redox Behavior of [H(6)(-)(n)()Ni(38)Pt(6)(CO)(48)](n)()(-) (n = 4-6) Anions: A Series of Metal Carbonyl Clusters Displaying Electron-Sink Features.

An investigation of the chemical and electrochemical redox behavior of the bimetallic [H(6)(-)(n)()Ni(38)Pt(6) (CO)(48)](n)()(-) (n = 4-6) clusters shows that they display electron-sink features encompassing up to six different oxidation states. As a corollary, these studies provide an indirect proof of the presence of hydride atoms where n = 4 and 5. The difference in the formal electrode potentials of consecutive redox couples of both [HNi(38)Pt(6) (CO)(48)](5)(-) and [Ni(38)Pt(6) (CO)(48)](6)(-) is almost constant and amounts on the average to ca. 0.33 and 0.28 V, respectively. Such constancy of DeltaE within each species points out the absence of a well-defined HOMO-LUMO gap in both clusters. Besides, its value is an indication of their semiconductor rather than metallic nature. A plot of the average DeltaE exhibited by the known carbonyl clusters displaying electrochemically reversible multiple redox changes versus their nuclearity suggests that the transition from semiconductor to metallic behavior might occur upon a ca. 50% increase of the today available cluster nuclearities.