Platinum oligomers

Similarly, when PtClg ions are irradiated in the presence of PA, which prevents coalescence, most of the Pt atoms are found via STM imaging in the form of very small platinum oligomers of 3-7 atoms only [92]. In the presence of PP, PtCle irradiated solutions present a UV band with a maximum at 215 nm [93]. About 20% of the initial signal is lost by oxidation when the sample is exposed to air, the rest being stable. This result again confirms that the redox potential of the smallest clusters is markedly shifted to the negative values. 

Newer silicone adhesives having solids levels up to 97% are also commercially available [109]. Instead of using silanol condensation reactions, they rely on addition chemistry between vinyl functional silicone oligomers and silicon hydride terminated silicones. This addition reaction is typically facilitated with platinum derived catalysts. This hydrosilation process can be run at reduced oven temperatures, but the finished products typically do not yield the same balance of properties as seen for condensation cure materials. 

There is significant metal-metal bonding in the platinum compound, whose geometry involves a square of platinum atoms another important difference is that the coordination geometry is square planar in palladium acetate but octahedral in the platinum analogue. Different oligomers exist in solution, broken down by adduct formation. Palladium(II) acetate may be obtained as brown crystals from the following reaction [65] ... 

The existence of materials now included among the conducting polymers has long been known. The first electrochemical syntheses and their characterization as insoluble systems took place well over a century ago. In 1862 Letheby reported the anodic oxidation of aniline in a solution of diluted sulphuric acid, and that the blue-black, shiny powder deposited on a platinum electrode was insoluble in HjO, alcohol, and other organic solvents. Further experiments, including analytical studies, led Goppelsroeder to postulate in 1876 that oligomers were formed by the oxidation of aniline. 

The nitrogen cleaning loop consists of a filter to remove any dust, a platinum catalyst bed to remove ethylene glycol, acetaldehyde and oligomers by combustion at quasi-stoichiometric oxygen ratios, and a gas dryer for the removal of moisture down to dew points below —40 °C. The oxygen content of the nitrogen is typically <10 ppm. 

Figure 2.9 Inductively coupled plasma detection of diaminodichloroplatinum(n). Conditions column, Shodex OH, 25 cm x 4.1 mm i.d. eluent, 0.01 m phosphoric acid flow rate, 1 ml min-1 detector, emission at platinum line 265.9 nm. Samples cis and trans diaminodichloroplatinums. The second peaks are considered to be their oligomers.

Oligomers, condensation, in formation of hy-droxo-bridged complexes, 32 91 Oligonucleotides, platinum binding, 37 185-187... 

Another example has been found in the author s laboratory. In the course of studies on the synthesis of metal-olefin complexes by means of cathodic reduction in dry organic mediums, a variety of linear oligomers were prepared on the nickel atom formed at the platinum cathode in electrolytic solution (32). The solution contained tetracispyridine nickel perchlorate or nickel dichloride and butadiene in ethanol or dimethoxye-thane, using tetrabutylammonium perchlorate as an electrolyte. 

Oxidative addition of the Si-aryl carbon bond in the silacyclobutene ring to Pt gives the optically active intermediate Pt-complex. Further coordination of (+)-l-methyl-l-(l-naphthyl)-2,3-benzosilacyclobut-2-ene to the complex and cr-bond metathesis will provide the cyclic dimer Pt-complex. Reductive elimination from the intermediate platinum complex gives cyclic polymers and oligomers. Preference of cr-bond metathesis over reductive elimination gives polymers of higher molecular weight. The presence of EtsSiH in the system results in the formation of linear products via cr-bond metathesis. 

Neckers and coworkers reported a similar polymerization using (chloromethyl)dichloro-methylsilane as a starting material (equation 15)162. Oligomers were obtained in addition to cyclic trimers and tetramers. In the presence of a platinum catalyst and tetravinylsilane, the oligomer crosslinked when irradiated to form a hard, porous material that could be pyrolyzed to a silicon carbide char containing excess carbon. A later report described other platinum photo- and thermal catalysts that could be used in this crosslinking reaction163. 

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