Sn complexes

From the obtained trajectories the following structural and electronic properties were extracted (i) structure factors, (ii) stability of Sn complexes, in particular, the Zintl anions, and (iii) the electrical conductivities - which yield answers to the questions mentioned in the first paragraph. 

At room temperature, trans-8 is formed, whereas at -78 °C mixtures of cis-8 and trans-8 are obtained. Pure cis-8, which rearranges to trans-8 at 20°C, is the product when Si2Cl6 is the starting material. Crystalline trans-8 is isomorphous with the respective Ge- and Sn- complexes (d Si-Cl 2.27, d Si-P 2.35 A). 

Quite recently, it was established that the formation of the pentacoordinated germanium and tin compounds EF4(CH2CH=CH2) from EF3(CH2CH=CH2) (E = Ge, Sn) by the addition of F is exothermic148. The nucleophilicity of the allylic y-carbon is much enhanced when the pentacoordinated EF4(CH2CH=CH2) is formed. These results are qualitatively similar to those found for the reaction of the corresponding silicon compound. The pentacoordinated Ge and Sn complexes have a significant Lewis acidity which allows them to form stable hexacoordinated intermediates in the course of the reaction. 

In the case of ethylene hydrogenation, the mechanism proposed by Parshall [61] involves the coordination of an alkene molecule through a five-coordinate intermediate (Eq. (13)) the subsequent alkene insertion into the Pt-H bond (Eq. (14)) and intervention of a second molecule of H2 (Eq. (15)) leads to the elimination of ethane and restoration of the catalytic active species [PtH(SnCl3)]2. However, in 1976 Yasumori and coworkers reported a kinetic analysis conducted on the hydrogenation of ethylene catalyzed by the Pt-Sn complex [(Me)4N]3[Pt(SnCl3)5] [70], under much milder conditions than those... 

Silastannation similarly appears to involve intermediates based on Si-PdL -Sn complexes, the rate-determining step being the insertion of the alkyne into the Sn-Pd bond (Equation (32)). 

The Pt-Sn complexes were studied extensively in the hydrogenation of vegetable oils to remove excessive unsaturation9. 

In the following section, we describe the case of adsorption of a Sn complex onto a palladium oxide suspension. In an alkaline medium (a basic PdO hydrosol), chlorides in the SnCL complex are substituted in the coordination sphere of tin(IV) by hydroxo anions, which are in excess, yielding the stannate Sn(OH)g complex. The Sn Mossbauer spectroscopy spectrum of a bimetallic sol (frozen in liquid nitrogen) is compared with a true stannic solution. At the same tin concentration, it shows the changes in the Sn environment due to adsorption onto the PdO surface (Fig. 13.27). The isomer shift S is found to be close to zero for the stannate solution and increases when contacted with the PdO suspension, indicating a modification of the coordination sphere of tin. The increase in 5 can be correlated to an increase in the core level electronic density of tin. The quadrupole splitting A, is related to a modification of the symmetry of the close environment of tin, due to adsorption of Sn(OH)g complexes onto the PdO colloidal nanoparticles. 

As judged by NMR investigation, hexacoordinate Sn complexes are not formed by the addition of excess chloride, aryloxide or HMPA to the pentacoordinate complexes 30a-32a, 33 -38226. 

Pt-Sn Pt-Sn complex in acetone impregnated on A1203 / - / Reduced in situ at 375 °C at elevated H2 pressure. XPS... 

As noted in the Introduction, the Pt-Sn system has been studied extensively, both from the standpoint of the structure of the catalyst as well as the reason for the superior catalytic properties. Davis utilized Pt-Sn complexes, including Pt3Sn8Cl22, in an organic solvent to prepare supported catalysts (42). It was proposed that the reason for the superior activity of catalysts prepared in this manner was the formation of a PtSn alloy (48,49). 

The analogous red EuCpj has been prepared by the sublimation of the THF solvated complex. The Eu complex is isostructural with the Sn complex [139]. The bent structure... 

It appears probable that the 2XeFs MF4 (M = Ge, Sn) complexes reported by Pullen and Cady will prove to be structurally related to [XeFs ]2[PdF6 ]. The ability of XeFe to donate F to a tetrafluoride to form [XeFj ]2-[PdF "] indicates that it is a moderately good base. It remains, however, to be seen if [XeFs JalMFg "] salts can be derived from the metal trifluorides. 

To remove the Oj requires pumping at 200-300°C, and at this temperature the bare Nil ions disproportionate to Ni i and Ni°. The [OjNiii— Sn)] complex is evidently more stable than Nii(Sn) itself. 

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