Platinum compounds parameters

Fig. 26. Tan 3 of a crosslinking PBD (Mw = 18 000) as a function of reaction time [31]. Parameter is the frequency co. The polymer is vulcanized at the pendant vinyl units with a bifunctional silane crosslinker using a platinum compound as catalyst. The curves intersect at the gel point resulting in...

CARBAMAZEPINE PLATINUM COMPOUNDS 1 plasma concentrations of antiepileptic, which t risk of seizures Due to impaired absorption of antiepileptic Monitor closely for seizure activity, and warn patient and carers. Need to adjust dosage using parameters such as blood levels to ensure therapeutic levels... 

An important parameter for electrochemical solutions is the range of the electrical potential within which they are electroinactive. In other words, the anodic or cathodic windows they have available in which investigations on the redox properties of various compounds can be performed. We have already reported in Table 1 Figure 9 shows graphically the potential ranges of the most common solutions at a platinum electrode. 

Hubbard (13) elucidated a mathematical description of the change from one situation to another for the simplest case of a half-filled s band of a solid. His result is shown in Figure 11. For ratios of W/U greater than the critical value of 2/ /3 then a Fermi surface should be found and the system can be a metal. This critical point is associated with the Mott transition from metal to insulator. At smaller values than this parameter, then, a correlation, or Hubbard, gap exists and the system is an antiferromagnetic insulator. Both the undoped 2-1 -4 compound and the nickel analog of the one dimensional platinum chain are systems of this type. At the far left-hand side of Figure 11 we show pictorially the orbital occupancy of the upper and lower Hubbard bands. 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

The benzyl and phenyl groups were removed by hydro-genolysis over palladium and platinum catalysts, respectively, and the acetyl groups by treatment with ammonia in methanol. In this case too, the monoammonium salt of the phosphorylated disaccharide 2 was isolated physical and chemical parameters of the compounds obtained by both methods were identical. 

Unfortunately, the redox potential of the Pt4 + /3+ couple is not known in literature. Although some stable Ptm compounds have been isolated and characterized (37), the oxidation state III is reached usually only in unstable intermediates of photoaquation reactions (38-40) and on titania surfaces as detected by time resolved diffuse reflectance spectroscopy (41). To estimate the potential of the reductive surface center one has to recall that the injection of an electron into the conduction band of titania (TH) occurs at pH = 7, as confirmed by photocurrent measurements. Therefore, the redox potential of the surface Pt4 + /3+ couple should be equal or more negative than —0.28 V, i.e., the flatband potential of 4.0% H2[PtClal/ TH at pH = 7. From these results a potential energy diagram can be constructed as summarized in Scheme 2 for 4.0% H2[PtCl6]/TH at pH = 7. It includes the experimentally obtained positions of valence and conduction band edges, estimated redox potentials of the excited state of the surface platinum complex and other relevant potentials taken from literature. An important remark which should be made here is concerned with the error of the estimated potentials. Usually they are measured in simplified systems - for instance in the absence of titania - while adsorption at the surface, presence of various redox couples and other parameters can influence their values. Therefore the presented data may be connected with a rather large error. 

Aromatic compounds are reduced over the six platinum metal group catalysts at widely different rates, as expected, but additionally the products of reduction frequently vary with the metal used. Many of these results may be correlated in terms of two parameters not obviously connected to aromatic properties the relative tendencies of these catalysts to promote double bond migration in olefins and to promote hydro-genolysis of vinylic and allylic functions. 

The extended Hiickel method, which is a semiempirical quantum chemistry method, is often used as a preliminary step in the DFT study of molecular orbital analysis. The acetylide-bridged organometallic dinuclear complexes 5.2 were studied by Halet et al. using the extended Hiickel method for qualitative analysis and DFT for additional electronic properties [97], The extended Hiickel analysis concluded that the main contribution of the Pt-C bond arises from ct type interactions while the n back-donation is very weak. The DFT/BP86 calculation gives a 2.371 eV HOMO-LUMO gap. The electronic communication parameter Hdb between the bis-ferrocene compound linked with platinum acetylide (5.3) was calculated to be 0.022 eV, compared with 0.025 eV obtained experimentally by Rapenne and coworkers using DFT and the extended Hiickel method [98],... 

Most of the reported results are given as evidence for structures in solution of compounds whose crystal structures are known from X-ray data. Some of them are completed by and P NMR spectra. We will give only the NMR parameters of these compounds using the chemical formulae. For more structural details, the reader can refer to the original publications. Platinum chemical shifts are referred to S = 21.4 MHz. In [Pt2Fe(dppm)2(CO)4], 5( Pt) = + 790 for the platinum atom bound to one phosphorus atom, and (i95pt)=+497 for the platinum bound to two phosphorus atoms, V(i 5pt,i95pt)= 1730 Hz [100]. Other results are presented in Table 20. 

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