Platinum complexes, comparison with

SAXS data showed that the molecules of the palladium complex [Pd2(PPh2)H c]n are nearly spherical in shape with a diameter of 15.6 A. EXAFS data showed that both the platinum, [(PPh2)Pt]8 -io, and palladium, [Pd2(PPh2)Hx] , complexes contained only phosphorus and metal atoms in the first coordination sphere. The interatomic distance between Pt(Pd) and the phosphorus atoms is 2.26 A, which is typical of the Pt(Pd)-P distances in platinum and palladium complexes. Comparison with the spectral data of the reference compound, Pd(PPh3)4, showed that each platinum atom is surrounded by four phosphorus atoms (the coordination number, u(P/Pt), is four). The corresponding value for palladium atoms, (P/Pd), is three. 

The shift in the C=C frequency, vi, for adsorbed ethylene relative to that in the gas phase is 23 cm-1. This is much greater than the 2 cm-1 shift that is observed on liquefaction (42) but is less than that found for complexes of silver salts (44) (about 40 cm-1) or platinum complexes (48) (105 cm-1). Often there is a correlation of the enthalpy of formation of complexes of ethylene to this frequency shift (44, 45). If we use the curve showing this correlation for heat of adsorption of ethylene on various molecular sieves (45), we find that a shift of 23 cm-1 should correspond to a heat of adsorption of 13.8 kcal. This value is in excellent agreement with the value of 14 kcal obtained for isosteric heats at low coverage. Thus, this comparison reinforces the conclusion that ethylene adsorbed on zinc oxide is best characterized as an olefin w-bonded to the surface, i.e., a surface w-complex. 

Palladium(IV) is a relatively rare oxidation state. The paucity of isolated complexes in comparison with PtIV has been ascribed to the much higher ionization potential required to produce Pd4+ (109.5 us. 97.16 eV for PtIV).303 Binary complexes with oxide and the chal-cogenides have been well characterized as have PdF4 and [PdXe]2- (X = F, Cl, Br). The chemistry of platinum group metals in higher oxidation states has been the subject of a recent review.304... 

Fig. 8 Absorption (left) and emission (right) spectra of the bis-(pyrenylacetylide) platinum complex 13 (solid lines) and of Pt(dbbpy)(-C=C-Ph)2 for comparison (dotted lines) in deoxygenated CH2CI2 at room temperature kex = 480 nm. Reprinted with permission from [32]. (2003) American Chemical Society...

The reactions of various platinum derivatives with Ru3(CO)12, Eqs. (15)—(18), were explored by Stone and co-workers (28, 30). As seen by comparison of Eqs. (14)—(18), the exact product that resulted was very dependent on the particular platinum complex employed. All of the reactions involved phosphine transfer from platinum to ruthenium during... 

Halogen-bridged platinum(II) complexes of the tertiary phosphines, arsines, etc., were then unknown and they had properties well worth studying for comparison with those of their palladium analogs. Also, they could be oxidized to platinum(IV)-bridged species, and these showed marked instability compared with their platinum(II) analogs. This led me to speculate that the electrons in the [Pg.7]

Optical spectroscopy has been applied with a good deal of success to the identification of chemisorbed species and of the nature of the surface bond. Infrared spectra have been most useful in studies of simple molecules, such as carbon monoxide adsorbed on platinum or nickel, and ultraviolet spectra for the characterisation of more complex interipediates, such as carbonium ions and ion radicals. The frequency of the adsorption band (or bands) often serves to identify the adsorbed species by comparison with spectra of known compounds. Quantitative information may then in principle be obtained by measuring the area under the adsorp-... 

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