Counter-anion

Table 11.17 Relative Selectivity of Various Counter Cations Table 11.18 Relative Selectivity of Various Counter Anions...

TABLE 11.18 Relative Selectivity of Various Counter Anions... 

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stabiHty. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkaH metals such as cesium, mbidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

Figure 28.3 (a) Silver(III) ethylenedibiguanide complex ion the counter anion can be HSO4, C104 , NOs" or OH . (b) Gold(III) (dimethylamino)phenyl complex ion the counter anion can be Bp4 or C104 . 

Effects of solvent polarity, counter-anion nucleophilidty, temperature, and monomer concentration on the carbenium ion polymerization chemistry have been extensively studied29,36 38,49. Based on previous knowledge26"29 Me3Al was chosen because with this coinitiator undesired chain transfer to monomer processes are absent. Preliminary experiments showed that Et3Al coinitiator did not yield PaMeSt, possibly because the nuc-leophilicity of the counter-anion Et3AlQe is too high and thus termination by hydrida-tion is faster than propagation36. ... 

These effects, however, are not unexpected. Previous authors have also found a reduction in M and conversion with decreasing medium polarity. Conceivably, reduced Mn s at reduced polarity are due to relatively faster termination, i.e., the nucleophilieity of the Me3AlCl counter-anion increases in relatively nonpolar media which results in... 

The x-ray crystal structures of the hexaethyl- and hexabutenylbenzene complexes show noteworthy conformational effects [78] (Fig. 6). The hexaethylbenzene complex has four distal chains [76] contrary to all the previous conformations of C6Et6 and (M)C6Et6 of C3 symmetry. This conformation also depends on the counter-anion as the three conformations with four, five, and six distal ET groups have close energies and can be observed by low-temperature 1H NMR. The hexabutenyl benzene complex has five distal chains [77]. 

Indeed, with the BPhT counter-anion, there are also five distal ET groups in FeCp(C5Et6) + BPh4 [79]. On the other hand, the five Et groups of FeCp (C5Et II)+ PF6 are all distal (the latter complex was specifically obtained from FeCp (CO)2Br and C6Et6, which may open the route to penta-alkylbenzenes from hexa-alkyl benzenes [80]). 

Figure 4. (A) Cyclic voltammograms over a range of scan rates for a redox polymer (poly-[Fe 5-amino-1,10-phenanthrotme)3]3+/>)91 and (B) p-doping and undoping of a conducting polymer (polypyrrole) (B). [(A) Reprinted from X. Ren and P. O. Pickup, Strong dependence of the election hopping rate in poly-tris(5-amino-1,10-phenan-throline)iron(HI/II) on the nature of the counter-anion J. Electroanal. Chem. 365, 289-292,1994, with kind permission from Elsevier Sciences S.A.]...

Where the second axial ligand or counter-anion is not known (e.g., in solution), this is indicated by . Dinuclear complexes are indicated by the addition of two Co atoms to the formula of the ligand, e.g., Co—CH=CH—Co. 

Fig. 1 Relative energy comparison between neutral and solvent coordinated cationic species, associated with counter anion CF [A], Br [B], and I [C].

Apparently, no bottles of aqueous ammonia are present in the laboratory, so the components of the buffer solution must come from the salts. The technician needs an ammonium salt with a counter anion that has no acid-base properties. Ammonium chloride (NH4 Cl) would be an appropriate choice. This salt contains the conjugate acid, NH4, and the technician can generate NH3 by adding strong base to the ammonium chloride solution NH4 ((2 q) + OH ((2 q) NH3((3 q) + H2 0(/)... 

Fig.1. Structures of porphyrin 1, chlorophyll 2, and phthalocyanine 3. In the presence of metal salts M"+X (M=metal, X=counter anion, n=oxidation state or number of counter anions), porphyrins produce chelate complexes. Some metal chelates of the porphyrins, such as ZnPor, form further coordination bonds with other ligands such as pyridines...

Fig. 6. Chemical reactions used for CPO formation reactions R, P porphyrin moieties, X halogen, A counter anion, and I ligand)...

In the opposite case to that considered above, Cs >ic2 and the difference in concentration Cs of the mobile electrolyte inside and outside the gel may be comparable in magnitude to the concentration C2/ of counter-anions. Hence the ion osmotic pressure is greatly reduced. Calculation of Cs — Cs for this case (see Appendix B) gives for the osmotic pressure due to the mobile ions... 

It is not clear whether the X anion remains ligated to the palladium(II) center. For example, for acetic acid, the palladium hydride was initially postulated as being HPd(OAc)L ,377,378 but more recently as HPdL +.367 To date, none of these complexes has been characterized.367 Oxidative addition of acetic acid or formic acid to a palladium(O) complex in DMF affords a cationic palladium hydride /ruw.v-I IPd(PPh3)2(DMF)+, with an acetate or a formate counter-anion. Both reactions are reversible and involve an unfavorable equilibrium so that a large excess of acid is required for the quantitative formation of the palladium hydride complex.379 This allows us to conclude that the catalytic reactions initiated by reaction of palladium(O) and acetic acid (or formic acid) proceed via a cationic palladium hydride trans-HPdfPPtHWDMF)"1", when they are performed in DMF.379... 

Open chain polyamine ligands have been widely studied. Often the coordination of zinc is compared with other first row transition metals and factors, such as behavior across a pH range, studied. The protonation patterns and stability constants are of particular interest. Octahedral zinc tris(ethylenediamine) structures have been characterized by X-ray diffraction with a number of different counter anions.94 The X-ray structure of zinc tris(ethylenediamine) with fluoride counter ions reveals extensive hydrogen bonding.95... 

In contrast to the nonmetals of the main group, elements the transition metals form only a relatively few compounds that are composed of simple isolated molecules, although they form many complex ions that exist as crystalline solids with an appropriate counter anion. 

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