Syntheses, Structures, and Electrochemistry of the Defectiveccp[Pt₃₃(CO)₃₈]^2–and thebcc[Pt₄₀(CO)₄₀]^6–Molecular Nanoclusters

Abstract

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 -4, -6 to -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 -4 to -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.

Functionalization, Modification, and Transformation of Platinum Chini Clusters

“…Compared to Chini clusters (CO/Pt = 2), these are CO‐poorer species (CO/Pt = 1.0–1.3) which are usually obtained by means of two general strategies:, (1) thermal decomposition of [Pt 3 n (CO) 6 n ] 2– ( n = 2–10) Chini clusters; (2) oxidation/reduction of preformed platinum carbonyl nanoclusters. The first examples of Pt browns were reported by Chini and Longoni in the seventies of last century,, but the number of species structurally characterized has considerably increased only in the recent years , …”

“…Selectivity usually decreases by increasing the nuclearity of the parent Chini cluster , . Therefore, whilst [Pt 19 (CO) 22 ] 4– may be obtained with high selectivity and yield by thermal treatment of [Pt 9 (CO) 18 ] 2– , larger clusters such as [Pt 24 (CO) 30 ] 2– , [Pt 26 (CO) 32 ] 2– , [Pt 33 (CO) 38 ] 2– , [Pt 38 (CO) 44 ] 2– and [Pt 44 (CO) 45 ] n – are usually obtained with lower yields and often as mixtures , . In addition, Pt browns are difficult to crystallize and, often, their crystals are poorly diffracting.…”

“…Pt browns can be alternatively obtained by the oxidation/reduction of preformed species. For instance, it has been reported that the products of the selective chemical oxidation of [Pt 19 (CO) 22 ] 4– , that is [Pt 19 (CO) 22 ] 3– , [Pt 19 (CO) 22 ] 2– and [Pt 19 (CO) 22 ] – , are not stable and evolve with time into larger clusters (Scheme ), such as [Pt 40 (CO) 40 ] 6– , [Pt 36 (CO) 44 ] 2– and [Pt 38 (CO) 44 ] 2– , . Similarly, [Pt 19 (CO) 22 ] 4– may be reduced to the penta‐anion [Pt 19 (CO) 22 ] 5– which is transformed, after workup, into [Pt 23 (CO) 27 ] 2– …”

“…Conversely, [Pt 36 (CO) 44 ] 2– and [Pt 33 (CO) 38 ] 2– possess defective ccp structures, that can be formally derived from the regular ccp metal cage of [Pt 38 (CO) 44 ] 2– by elimination of 2 and 5 Pt atoms, respectively (Figure ). When defects are introduced, localized deformations of the metal cage occur which tend to eliminate and repair such defects , …”

“…Selected infrared spectra of (a) [Pt 33 (CO) 38 ] n and (b) [Pt 40 (CO) 40 ] n as a function of the cluster charge n , and of the potential E. Adapted with permission from ref . Copyright 2016 American Chemical Society.…”