Syntheses, Structures, and Electrochemistry of the Defective ccp [Pt33(CO)38]2- and the bcc [Pt40(CO)40]6- Molecular Nanoclusters

The molecular [Pt33(CO)38]2- nanocluster was obtained from the thermal decomposition of Na2[Pt15(CO)30] in methanol. The reaction of [Pt19(CO)22]4- with acids (1-2 equiv) affords the unstable [Pt19(CO)22]3- trianion, which evolves with time leading eventually to the [Pt40(CO)40]6- hexa-Anion. The total structures of both nanoclusters were determined via single-crystal X-ray diffraction. [Pt33(CO)38]2- displays a defective ccp Pt33 core and shows that localized deformations occur in correspondence of atomic defects to "repair" them. In contrast, [Pt40(CO)40]6- shows a bcc Pt40 core and represents the largest Pt cluster with a body-centered structure. The rich electrochemistry of the two high-nuclearity platinum carbonyl clusters was studied by cyclic voltammetry and electrochemical in situ Fourier transform infrared spectroscopy. The redox changes of [Pt33(CO)38]2- show features of chemical reversibility and electrochemical quasi-reversibility, and the vibrational spectra in the CO stretching region of the nine redox forms of the cluster [Pt33(CO)38]n (n = 0 to \ue2'4, \ue2'6 to \ue2'9) are reported. Almost all the redox processes exhibited by [Pt40(CO)40]6- are chemically and electrochemically reversible, and the eight oxidation states of [Pt40(CO)40] from \ue2'4 to \ue2'11 were spectroscopically characterized. The effect of the more regular bcc Pt-carbonyl cluster structure of [Pt40(CO)40]6- with respect to that of the defective ccp Pt33 core on the redox behavior is discussed