Palladium ion

It was found that sorbed palladium might catalyse reaction of Mn(III) reduction by Cf not only after it s removing from coal, but AC with palladium, Pd/AC, has also his own catalytic effect. On the base of dependence between characteristics of AC, chemical state of palladium on AC surface and catalytic action of Pd/AC in indicator reaction it might establish, that catalytic action concerns only to non-reduced or partly reduced palladium ions connected with chloride ions on coal surface. The presence or absence of catalytic action of Pd/AC in above-mentioned reaction may be proposed for determination of chemical state of palladium on AC surface. Catalytic effect was also used for palladium micro-amounts determination by soi ption-catalytic method. 

Other one-pot preparations of bimetallic nanoparticles include NOct4(BHEt3) reduction of platinum and ruthenium chlorides to provide Pto.sRuo.s nanoparticles by Bonnemann et al. [65-67] sonochemical reduction of gold and palladium ions to provide AuPd nanoparticles by Mizukoshi et al. [68,69] and NaBH4 reduction of dend-rimer—PtCl4 and -PtCl " complexes to provide dend-rimer-stabilized PdPt nanoparticles by Crooks et al. [70]. 

Octaethylbilindione (H3OEB) is a convenient model for the bile pigment biliverdin IXa. Key redox states of this ligand as observed in its complexes are shown in Figure 14. The redox behavior of the palladium complex of octaethylbilindione was examined in order to determine the generality of the redox behavior of this group of transition metal complexes.202 A preliminary report on the novel tetrameric Pd4(OEB)2, which contains palladium) ) ions 7r-bonded to C=C bonds of the tetrapyrrole ligand, and of Pdn(OEB ) has appeared.203... 

Huang, K.C. and Ehrman, S.H. (2007) Synthesis of iron nanopartides via chemical reduction with palladium ion seeds. Langmuir, 23 (3), 1419—1426. 

Olefins and palladium ions PdCI42 form the following two types of complexes in an aqueous solution [247],... 

The reaction is highly exothermic as one might expect for an oxidation reaction. The mechanism is shown in Figure 15.1. Palladium chloride is the catalyst, which occurs as the tetrachloropalladate in solution, the resting state of the catalyst. Two chloride ions are replaced by water and ethene. Then the key-step occurs, the attack of a second water molecule (or hydroxide) to the ethene molecule activated towards a nucleophilic attack by co-ordination to the electrophilic palladium ion. The nucleophilic attack of a nucleophile on an alkene coordinated to palladium is typical of Wacker type reactions. 

The polymer resulting from oxidation of 3,5-dimethyl aniline with palladium was also studied by transmission electron microscopy (Mallick et al. 2005). As it turned out, the polymer was formed in nanofibers. During oxidative polymerization, palladium ions were reduced and formed palladium metal. The generated metal was uniformly dispersed between the polymer nanofibers as nanoparticles of 2 mm size. So, Mallick et al. (2005) achieved a polymer- metal intimate composite material. This work should be juxtaposed to an observation by Newman and Blanchard (2006) that reaction between 4-aminophenol and hydrogen tetrachloroaurate leads to polyaniline (bearing hydroxyl groups) and metallic gold as nanoparticles. Such metal nanoparticles can well be of importance in the field of sensors, catalysis, and electronics with improved performance. 

The details of the organic chemistry of the reaction of ethylene with PdCl2 (equation (1) above) are also known and are shown in Fig. 9.2. The palladium ion complexes with ethylene and water molecules and the water adds across the bond while still complexed to palladium. The palladium then serves as a hydrogen acceptor while the double bond reforms. Keto-enol tautomerism takes place, followed by release of an acetaldehyde molecule from the palladium. 

The reduction of Cu to Cu in the zeolite lattice is more difficult than reduction of platinum and palladium ions but easier than that of other transition metal ions.25 The resulting Cu" " ion in the zeolite is fairly stable both in a reductive atmosphere and imder degassing treatment at elevated temperatures, wh eas the precious metal ions are easily reduced to the respective metals and collect to yield metal particles. Die easy reducibility of Cu and the stability of Cu" " lead to a reversible redox behaivor betweoi Cu and Cu and result in the iqipearance of the specific catalytic activity. 

Another p-n junction-based hydrogen sensor has been produced by implanting palladium ions into 6H n-type SiC material [67]. Gold-plated copper contacted the p-n junction device. The gas response was measured as (small) changes in current as the gas ambient was varied between air and 4% in argon in the temperature range 23-240°C. For an absolute voltage above 1.2V, the p-n junction broke down. 

When palladium ions are bound to poly(ethyleneimine), a soluble polychelatogen, selective conversion of 2-pentyne to ds-2-pentene is achieved under mild conditions (20°C, 1 atm H2, 98% stereoselectivity).170 A dramatic reversal of stereoselectivity (selective formation of frans-2-pentene) is observed, however, if a spacious ligand such as benzonitrile is bound to palladium. 

For sample A, the electron density appearing on SI sites (6) at x = y = z = 0.045 was attributed without any ambiguity to palladium ions because of the short SI -0(3) distance (2.0 A) and the large amount of scattering matter corresponding to about 10 Pd2+. Sites SI and SI1 were assigned to palladium and sodium ions, respectively, although some Na+ may be mixed with Pd2+ in the former. 

Pd2+ tend to be the most dispersed among the eight sodalite cages, and bridged palladium ions are unlikely to occur. In conclusion, palladium ions exhibit behavior similar to that of Cu2+ (3) whereas Ni2+ ions mainly occupy SI sites in Y zeolites (7-8). 

Nature of Palladium in Hydrogen-Reduced Samples. In the above discussion, palladium ions were assumed to be reduced from Pd2+ to Pd(0). This assumption needs further discussion. First, the pattern of our results is well explained by assuming that isolated palladium atoms may exist in the sodalite cages after reduction by H2 up to about 200° C under our experimental conditions. Moreover, this assumption is in good agreement with infrared results obtained for similar samples. Some Pd+ ions may be also formed during the reduction, but quantitative measurements show that the amount of Pd+ does not exceed 10% of the reduced palladium (11). 

In connection with the structure of carbonyl metal complexes, these bands seem to be the result of the symmetric and the antisymmetric stretching vibrations of two CO molecules bonded linearly with the same Pd(II) ion. Imelik et al. (23) have shown that palladium ions are trigonally coordinated in Si, sites (d Om-Pd = 2 A). Because of chemisorbed CO, the palladium ions acquire a trigonal bypyramidal coordination. 

Loaded palladium is usually found as Pd(II) ions in zeolites. However, oxygen treatment leaves few palladium ions in the unusual Pd(III) form while in vacuo calcination forms Pd(I) ions. 

Palladium ions were reduced by hydrogen at room temperature. The zeolite thus formed has hydroxyl groups identical to those found in de-cationated Y zeolites and probably has a Bronsted acid character. Furthermore, hydrogen reduction produces metallic palladium almost atomically, dispersed within the zeolite framework as demonstrated by our IR, volumetric, and x-ray (23) results. Palladium atoms are located near Lewis acid sites which have a strong electron affinity. Electron transfer between palladium atoms and Lewis acid sites occurs, leaving some palladium atoms as Pd(I). Reduction by hydrogen at higher temperatures leads to a solid in which metal palladium particles are present. The behavior of these particles for CO adsorption seems to be identical to that of palladium on other supports. 

Many 1,2,4-triazines form complexes with metal ions and can be used for their determination. Thus, 3- and/or 5-(2-pyridyl)-substituted 1,2,4-triazines (e.g. 820) can be used for the determination of iron (II), cobalt(II), nickel(II), zinc(II) and copper(I) ions, thallium and palladium ions can be analyzed by 6-phenyl- (821a) and 5,6-diphenyl-l,2,4-triazine-3-thione (821b), while osmium can be determined by 3-thioxo-l,2,4-triazin-5-one (822), 3-thioxo-dihydro-l,2,4-triazin-5-one (823), 6-mercapto-l,2,4-triazine-3,5-dione (824a), 6-mercapto-5-thioxo-l,2,4-triazin-3-one (824b) and 3,5-dithioxo-l,2,4-triazine-6-carboxyl-ates (825) <78HC(33)189, p. 1004). 

Nucleation is performed by immersion of a sensitized nonconductor into the nucleating solution for 0.5-2 mins. The surface reaction between the stannous ions, Sn2+, adsorbed on the surface of the substrate and the palladium ions, Pd2+, in the nucleator solution is... 

Coordination of flexible amidic structures to the palladium ion resulted in the formation of a rigid hydrophobic cavity of 61 [82]. This self-assembly takes place in water, and aromatic carboxylates are recognized in it. It was found using NMR titration in D20 (pD=8.5, borate buffer). The structure of the complex formed is shown schematically in Fig. 4. It is apparent that cooperative binding of both carboxylates is essential for the stability of the complex formed nevertheless, the enantioselection of carboxylates is only very weak (Table 5). 

Bidleman et al. (2JD) used a palladium chloride-calcein chelate spray for organothiophosphorus compounds and detected 10 ng per spot. The mechanism is based on the release of the ligand because of the affinity of palladium ions for sulfur atoms. The technique does not necessitate bromine vapours and is therefore an improvement in terms of selectivity. Unfortunately, the reaction is slow and the fluorescence increases with time. 

In this section we shall try to review available data on catalytic properties of electron-deficient palladium on supported catalysts. The term electron deficient we shall consider to mean very small clusters of Pd on various supports, and/or palladium ions stabilized by virtue of their presence in an appropriate chemical environment. 

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