Platinum clusters and colloids

In a typical experiment, a solution of Pt4(OAc)g and phen monohydrate (2 1 initial Pt/phen mole ratio) in glacial AcOH was stirred successively under Ha and O2 (1 atm) at 20 °C  

Contrary to expectation, the reaction product 8, a black amorphous powder soluble in water and acetic acid, was found to have composition and properties quite different from those expected for the platinum analog of the Pdsgi giant clus-ter.157] According to elemental analysis, substance 8 has the reproducible elemental composition Pt8phen3(0Ac)4(0H)4(H20)6, which is quite different from the expected minimum formula Pt9(phen)o.96(OAc)2.89 for the Pt analog of palladium giant cluster 6. On the basis of the elemental composition, the formal oxidation state of platinum in substance 8 is close to (+1). This value was confirmed by the EXAFS data.  

Because of difficulties in determining the molecular mass of complex 8, the size of its molecule was estimated on the basis of SAXS data, from which particles 8 were found to be nearly spherical in shape with a mean diameter of 30 + 5 A. 

Transmission electron microscopy (TEM, HREM), on the other hand, revealed the metal cores of 8 to be particles also close to spherical in shape but with the mean diameter 14-18 A fringes typical of regular metal packing within the observed particles were also faintly visible on the micrographs (Fig. 5a). 

In accordance with this, the electron diffraction pattern of sample 8 contains nothing but barely perceptible, poorly reproducible diffraction rings without reasonable regularity in their arrangement.  

---