Pfeiffer complex

Fig. 19 summarizes the results for the particularly interesting group of the Pfeiffer complexes (N2O2). The range of scatter shown corresponds to the in-... 

Fig. 19. Pfeiffer complexes. Influence of the central atom on the oxygen activity of the Pfeiffer complexes. (Electrolyte Carbonate/bicarbonate buffer solution)...

While e. g. MnPc is completely inactive in both sulfuric acid and buffer solution, the Pfeiffer complex of Mn shows even greater activity than the Fe compound. The activity decreases in the order... 

Influence of the organic skeleton. The example of the Pfeiffer complexes makes it clear that the influence of the organic skeleton is of subordinate importance. Figure 20 shows this influence for a number of Co—N4 complexes. Here too, the differences in activity are much less than those produced by varying the central atom or the coordination. 

Other metal ligands that can bind oxygen have also been tested for oxygen reduction, such as porphyrins, thiospinels, and diamine (Pfeiffer) complexes (284, 285). Porphyrin complexes (Fig. 22) were the most active, even better than phthalocyanines, with activity decreasing in the order Co(II) > Fe(ni) > Ni(II) Cu(II). Figure 23 shows potential-current curves for some phthalocyanine and porphyrin electrocatalysts. The higher the current at a given potential, the more active is the catalyst. 

In contrast, chromium (ITT) and cobalt(III) form 2 1 dye metal complexes that have nonplanar stmctures. Geometrical isomerism exists. The (9,(9 -dihydroxyazo dyes (22) form the Drew-Pfitzner or y rtype (23) (A = C = O) whereas o-hydroxy—o -carboxyazo dyes (24) form the Pfeiffer-Schetty or fac type (25), where A = CO 2 and C = O. 

Pfeiffer (1913) pointed out that [Pt(PR3)X2]2 complexes can potentially exist in three isomeric forms, but only the symmetric frans-isomer has been characterized (Figure 3.40). 

Utilization of the Pfeiffer effect and outer-sphere complexation for the prediction of absolute configurations of optically active metal complexes. S. Kirschner and I. Bakkar, Coord. Chem. Rev., 1982,43, 325-335 (27). 

Stability constants for a series of M2+ cations, including Ca2+, with A23187 and with ionomycin have been determined in methanol-water mixtures (Taylor, R. W. Pfeiffer, D. R. Chapman, C. J. Craig, M. E. Thomas, T. P. Pure Appl. Chem. 1993, 65, 579-584) the estimation of stability constants for complexes of the anti-fungal antibiotic pradimicin (BMY-28864) with alkaline earth cations is complicated by the tendency of this antibiotic to aggregate (Hu, M. Ishizuka, Y. Igarashi, Y. Oki, T. Nakanishi, H. Spectrochim. Acta A 1999, 56, 181-191). 

We have referred to the influence of hydrogen bonding in one-component systems and mentioned the two-component system benzoic acid-pyridine (108). A variety of acid-base systems in addition to the latter are known to give 1 1 complexes. Pfeiffer gives in his book (88) a wealth of information from the older literature on such complexes, as well as on two-component organic-inorganic systems and charge-transfer complexes. 

In 1893 Werner founded his new constitutional formula for inorganic compounds, applied the theory to the systematic classification of the chromi-ammines, and found that all the chromi-ammines which had been investigated could be fitted in to his system of classification. Since then the chemistry of the chromi-ammines has been further developed hv Werner, Pfeiffer, and many others relationships have been traced between chromi-ammines, complex salts, and chromic salt hydrates, and numerous cases of isomerism have been discovered in this series of ammines. 

A series of salts is known of the above type where ethylenediamine and propylenediamine enter the chromic complex, giving rise to mixed salts. This series was described by Pfeiffer in 1908.6... 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

Univalent halides—e.g. NH l.AgCl CsCl.CuCl 2KCl.CuCl etc. The halides of the alkali metals do not often unite together to form stable complexes. Univalent copper, silver, and gold form double chlorides with the alkali halides, while the corresponding double bromides of silver and gold and the double iodide of silver have not been made. The facts can be summarized in the form of a scheme due to P. Pfeiffer (1902), where the hyphens represent compounds which have not yet been prepared ... 

The complex fluorides are in many ways closely analogous with the complex salts of the other halogens, but, owing to the pecul iarity of the alkali fluorideB in uniting in a bimolecular form with the metal fluorides, a new factor comeB into consideration, and this introduces so many c mplications that the likeness appears less than it real.y iB.—P. Pfeiffer (1902). 

The coordination chemistry of chromium(III) was first seriously investigated by Pfeiffer at the turn of the century in many ways his studies parallel the work of Werner on cobalt(III). The complexes of chromium(III) are almost exclusively six-coordinate with an octahedral disposition of the ligands. Many are monomeric ((Jeff 3.6 BM), although hydroxy-bridged and other polynuclear complexes are known in which spins on neighbouring chromiums are coupled. 

The Pfeiffer effect (the shift in a chiral equilibrium on the addition of an optical isomer of a different compound) of racemic [Cr(ox)3]3- has been examined using for the first time optically stable metal complexes cis-[MXY(AA)2]"+ (where M = Cr3+ or Co, AA = en or tmd and X and Y = anionic monodentate ligand). It was found that the chiral equilibrium of [Cr(ox)3]3-was always displaced in favour of its A enantiomer in the presence of A enantiomers of the cis complexes, and it is proposed that the absolute configurations of cis complexes could be inferred from the equilibrium shift induced in [Cr(ox)3], 438 Laser irradiation of an aqueous solution of racemic [Cr(ox)2(phen)] or [Cr(ox)(phen)2]+ in the presence of ( + )- or (- )-cinchonine hydrochloride rapidly shifts the chiral equilibrium in a direction opposite to that induced by the usual Pfeiffer effect in the dark.439... 

The linear trinuclear cation (100) and the tetranuclear cations (101) to (103)448-450 (Table 52) exist with mononuclear complexes in aqueous ethylenediamine buffer solutions in which equilibrium has been established by the catalytic effect of Cr2+ and charcoal under well-specified conditions.358 The cations were separated by ion exchange chromatography and fractional crystallization, and isolated as various salts (Table 52). The tetranuclear (rhodoso) compound (104)4S1 has been reprepared448 by a modification of Pfeiffer s method. 

The Pfeiffer effect is a term used to describe changes in the optical activity of solutions containing a chiral compound (the environmental substance ) on the addition of a racemic dissymmetric complex. The effect is generally attributed to a shift in the position of the equilibrium between d and l isomers for the racemic complex. The exact mechanism involved in mediating the chiral interaction is unknown. Perhaps surprisingly, both environmental substance and complex may simultaneously be cations. Studies of the Pfeiffer effect usually involve a moderately labile racemic complex [Cr(ox)3]3 is a popular choice for such studies, summarized in Table 82. Other studies of the optical activity of tris oxalates include work on photoinduced optical activity,898 photoracemization899 and the solid-state racemization of K3[Cr(ox)3]. 900 901... 

The complexes [Cr(S2CNMe2)3], [Cr S2P(OEt)2 3] and [Cr(S2COEt)3] have Pfeiffer CD activity but this develops only when there is a large ratio of optically active environment compound to the racemate.1021 A normal coordinate analysis of the IR spectra of [Cr(S2CNR2)3] (where R = Me, Et, Pr or Bun) has shown that the alkyl substituent affects the thioureide band at ca. 1550 cm"1 through kinematic as well as electronic effects.1022... 

Even so great an admirer of Werner as Paul Pfeiffer (1875-1951),93 Werner s former student and one-time chief of staff at the University of Zurich and the man who first applied Werner s theory to crystal structures (see Section 1.1.5.4), proposed modifications of the coordination theory. He applied what he called the principle of affinity adjustment of the valencies to overcome certain shortcomings of Werner s theory.94 He considered the ionizable radicals or atoms in the outer sphere to be combined with the complex radical as a whole and not attached definitely to the central atom or to any of its associated molecules. He also applied this idea to complex organic molecular compounds. However, Pfeiffer s modifications should not be interpreted as attacks on Werner s ideas. 

Werner apparently did not realize that the polynuclear complexes which he investigated so extensively95 constituted a transition between the usual mononuclear coordination compounds and the infinite structure of the crystal lattice. It remained for Paul Pfeiffer, Paul Niggli (1888—1953) and others to point out that crystal structures were in beautiful agreement with his coordination theory, as revealed by the then new experimental technique of X-ray diffraction.96... 

It is well over 40 years since Pfeiffer discovered that certain reactions of a-amino acid esters, in particular, ester exchange, racemization and oxygenation, are effected very readily when their Schiff bases with salicylaldehyde are complexed to a transition metal ion (most notably Cu11). The Schiff bases result from a condensation reaction between a reactive carbonyl group and the amino group of the amino acids. Snell and his co-workers43 were also one of the first to point out that similar reactions also occurred if pyridoxal was used instead of salicylaldehyde, and that there is a close analogy with pyridoxal phosphate-promoted enzymic reactions of a-amino acid metabolism. Since then much work has been due on these and other similar systems and their reactivities. 

A number of studies have been carried out on the ligand reactivities of the metal complexes of Schiff bases derived from amino acid esters and carbonyl compounds. Ester exchange reactions were first reported by Pfeiffer et a/.492 and extended by other investigators.493 496... 

In the fac configuration, also called the Pfeiffer-Schetty structure, nine isomers are possible four pairs of enantiomers and a centrosymmetric structure. Since the ligands are arranged parallel to one another, they sometimes are called sandwich complexes. The two mer and the nine fac orientations are depicted in [30],... 

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