The molecular [Pt-33(CO)(38)](2-) nanocluster was obtained from the thermal decomposition of Na-2[Pt-15(CO)(30)] in methanol. The reaction of [Pt-19(CO)(22)](4-) with acids (1-2 equiv) affords the unstable [Pt-19(CO)(22)](3-) trianion, which evolves with time leading eventually to the [Pt-40(CO)(40)](8-) hexa-anion. The total structures of both nanoclusters were determined via single-crystal X-ray diffraction. [Pt-33(CO)(38)](2-) displays a defective ccp Pt-33 core and shows that localized deformations occur in correspondence of atomic defects to "repair" them. In contrast, [Pt-40(CO)(40)](6-) shows a bcc Pt-40 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 [Pt-33(CO)(30)](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 [Pt-33(CO)(38)](n) (n = 0 to -4, -6 to -9) are reported. Almost all the redox processes exhibited by [Pt-40(CO)(40)](6-) are chemically and electrochemically reversible, and the eight oxidation states of [Pt-40(CO)(40)] from -4 to -11 were spectroscopically characterized. The effect of the more regular bcc Pt-carbonyl cluster structure of [Pt-40(CO)(40)](8-) with respect to that of the defective ccp Pt-33 core on the redox behavior is discussed.