PtNi

PtNi Reduction Aromatic nitro compound - Higher than mono-NP - [109]... 

In addition to surfactant-stabilized colloids, there has been work on forming metal colloids without stabilizers. Lee et al. have shown that direct reduction of mefal chloride salts in tetrahydrofuran with LiBH4 gives small nanoparticles that can be impregnated onto carbon. No further treatment is required after the removal of the solvent. This route was applied to the preparation of PfRu, PtNi, PtMo, and PtW particles. 

Another route that has been used recently to prepare Ft bimetal-lies (FtRu, i PtNi, and PtCr ) is via metal carbonyl chemistry. In this method, metal carbonyl complexes (either preformed or formed in situ)... 

The reduction of platinum(IV) complexes involves two one-equivalent changes PtIV- Ptni— Ptn the first step is rate-determining. Second-order rate constants with vanadium(II) (kv) and with hexaammineruthenium(II) (A Ru) show linear correlation (equation 6).171... 

As for the hydrolysis of the axial aqua ligand, pKa values were determined for the 1-methyluracilate-bridged /TT-02N(9-[Ptra]2-(9H2 by means of potentiometric titration (Xhi,OH2 = 3.2 x 10-4 m, h2,OH2 = 2.0 x 10-7 m) [60]. In addition, it was also suggested that the first ligation in Eqn. 5 selectively occurs at one of the two chemically nonequivalent Pt atoms of HH-[Ptni]2, as a clear isosbestic point was observed when the first ligation was dominating [54][56][59]. 

Bocarsly, Pfennig and co workers reported interesting multi electron photoreac tions for the trimeric M" Ptlv M" complexes 25a-c.212 215 In this system, a single photon excitation into the intervalence charge transfer band results dissociation of the trimer into [Pt(NH3)4]2+ and two equivalents of a M111. The initial photoexcited complex is though to dissociate first to a Mm complex and Ptni-Mn intermediate. The latter dimer subsequently undergoes a thermal electron transfer reaction to yield the final products. 

The first mixed-metal complex with a quadruply bridged structure, [PtNi(4-mpyt)4(MeCN)], was prepared by the reaction of [Pt(4-mpytH)4] CI2 with nickel acetate in the presence of potassium bicarbonate in naphthalene as a solvent at 120 C (102). 

Structural analysis disclosed that the PtNi complex takes a 4S geometry with the Pt atom coordinated by four sulfur atoms (Fig. 17). Acetonitrile is coordinated to the Ni site at the axial position to make the nickel ion hexacoordinated, including the neighboring platinum ion. The mean Pt - Ni distance (2.539 A Table I) is considerably shorter than the Pt Pt distance of [Pt2(4-mpyt)4]. 

Fig. 7. Evolution of surface and subsurface composition of a sputtered PtNi alloy during annealing. Top schematic view bottom STM images of a Pt25Ni75(lll) sample (100x90 nm each) corresponding to these states. The misfit dislocations between the altered layer and the bulk are visible as a network of dark lines in the middle STM image (cf. Refs. 45,46).

Turning to fcc(lll) surfaces, let us first compare the bulk properties of the alloys under consideration (Table 2). Stoichiometric PtFe, PtCo and PtNi form LIq phases in the bulk, characterised by an increase of the number of unlike nearest neighbours (8) with respect to an fee random alloy with 50% Pt (6 unlike NN). PtCu forms the peculiar LI, ordered phase, where the number... 

This shows us that the ordering tendency decreases in the sequence PtFe, PtNi and PtCo. 

Fig. 10. STM images of fcc(l 11) alloy surfaces. The bright atoms are Pt in PtCo and PtCu, but Fe in PtFe and Ni in PtNi. Compositions given are bulk compositions, except for PtFe, which is a surface alloy with =8 PtFe layers obtained by annealing a4 ML Fe film on Pt(111). The ordering of the PtFe alloy depends on the preparation frame (a) corresponds to an annealing tem-peramre of 470 °C, frame (b) to 530 C.

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