Redox behavior of [H6-nNi38Pt6(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 [H6-nNi38Pt6 (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 [HNi38Pt6 (CO)(48)](5-) and [Ni38Pt6 (CO)(48)](6-) is almost constant and amounts on the average to ca. 0.33 and 0.28 V, respectively. Such constancy of Delta E 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 Delta E 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