Ionization of the metal

The model of metal-ammonia solutions that has emerged is based on ionization of the metal atoms to produce metal ions and electrons that are both solvated. The solvated electron is believed to reside in a cavity in ammonia, and thus it may behave as a particle in a three-dimensional box with quantized energy levels. Transitions between the energy levels may give rise to absorption of light and thereby cause the solutions to be colored. The dissolution process can be represented as... 

The importance of ionization of the metal-sulfur bond in the electron-transfer process accounts for inhibitory properties being observed only for compounds of types I and II. Support for this mechanism was also obtained by the isolation of the disulfide (IV) from a reaction between peroxy radicals and zinc diisopropyl dithiophosphate. 

The first two bands in the UPS of Ni(PF3)4 (Fig. 26) are remarkably similar to those of Ni(CO)4 and hence can be assigned to the 2 7 2 and 2 E ionic states, which are produced by electron elimination from the t2 and e MOs of predominantly Ni(3d) character (20). The UPS of Pd(PF3)4 and Pt(PF3)4 can be assigned analogously (Table XXVII and Fig. 26) (20). The heavy atom effect (172) is clearly operative in this triad in the sense that the relative intensities of the spectral peaks are in the order Pt > Pd > Ni. The next two bands in the UPS of Ni(PF3)4 correspond to the ionization of the metal-phosphorus a bonds of symmetries t2 and a,. The latter ionization is not detectable in the UPS of the heavier metal compounds and, presumably, is obscured by peaks of higher intensity. [Note that there are some differences between the preliminary reports (152, 182) and a subsequent full paper (20) regarding the spectra and assignments. For example, the weak 14.7 eV band of Ni(PF3)4 was not detected in one report (152). This band was detected in... 

As in the case ofFe(CO)s the metal d orbitals ofFe(PF3)s and Ru(PF3)5 split into a[, e, and e" levels in D3h symmetry, and both doubly degenerate MOs are fully occupied (Table XXVII). The first two UPS peaks of these compounds therefore correspond to the production of the 2E and 2E" Fe 3cMike ionic states. Group theoretical considerations indicate that 2E, 2 A (2), and 2A 2 ionic states should arise from ionization of the metal-phosphorus o-bonding MOs. These ionizations are evidently degenerate in Fe(PF3)s, and only three of the four ionizations are detectable in Ru(PF3)s (169). The assignments in Table XXVIII should therefore be viewed with caution. 

It is evident from the trends pertaining to the ionization of the metal-carbon o bonds of r2 symmetry that the IEs are less for the Me3XCH2-substituted compounds than for the methylated compounds. On the basis of Koopmans theorem this would imply that the metal-carbon bonding is weaker in the Me3XCH2 derivatives. 

UPS studies of some dithiocarbamates (50) and acetylacetoneiminato (64, 130a) complexes have also been reported. Precise assignments have not been made however, the ionization of the metal-localized MOs appears at higher energy than those of the ligand-type MOs. Comparable studies of diethyldithio-phosphate (212) and difluorodithiophosphate (6) complexes of several metal ions have also been reported. 

Jensen and Padley (1 ) determined an equilibrium constant for the reaction Cs(g) + H20(g) CsOH(g) + H(g) at 2475 K by atomic absorption spectroscopy in a hydrogen-oxygen-nitrogen flame. These workers pointed out that interference from ionization of the metal had introduced some uncertainty in their equilibrium data. Using all JANAF functions (2), 3rd law analysis of the equilibrium constant gives A H (298.15 K) = 27.4 kcal mol". This leads to an enthalpy of formation,... 

Deviations from linearity at low concentrations are often the result of significant ionization of the analyte. When a high concentration of an easily ionized metal salt is added, the ionization of the analyte is suppressed because of the electrons produced by ionization of the metal. 

Similar solution behavior was reported(9-11) for sulfonate ionomers. Rochas eit al. (9) observed a polyelectrolyte effect for acrylonitrile-methallylsulfonate copolymers in DMF. Lundberg and Phillips(10) studied the effect of solvents, with dielectric constants ranging from c 2.2 to e 46.7, on the dilute solution viscosity of the sulfonic acid and Na-salt derivatives of sul-fonated polystyrene (SPS). For highly polar solvents such as DMF and dlmethylsulfoxide (DMSO, e 46.7) they observed a polyelectrolyte effect, but for relatively non-polar solvents such as THF and dioxane (c = 2.2) no polyelectrolyte effect was observed. Like Schade and Gartner, these authors concluded that polar solvents favor ionization of the metal sulfonate group while non-polar solvents favor ion-pair interactions. 

Hittorf (1900) ascribed passivity to an induced change in the nature of the metallic surface (Zwangzustand). According to Finkelstein (1902) the metal in the passive state is transformed into a nobler modification, whereas LeBlanc (1903) ascribed the state to a change in the velocity of ionization of the metal. 

Part of the ionization of the metallic neutral species X may occur during ablation, but most of the ions are probably produced by photoionization... 

The pKa values [taken from Sillen and Martell (14) and references cited therein] for the ionization of the metal ion aquo-complex [Eq. (6)]... 

The role of the metal ion in ester hydrolysis catalysed by CPA has been examined with both Zn +- and Co +-substituted enzymes. When the terminal carboxyl of the substrate is electrostatically linked to argenine-145 and the aromatic side-chain lies in a hydrophobic pocket, the only residues close enough to the substrate to enter catalysis are glutamate-270, tyrosine-248, the metal ion, and its associated water. Low-temperature studies aid the elucidation of the mechanism. Between - 25 and - 45 °C in ethylene glycol-water mixtures two kinetically discrete processes are detected, the slower of which corresponds to the catalytic rate constant. The faster reaction is interpreted as deacylation of a mixed anhydride acyl-enzyme intermediate formed by nucleophilic attack by glutamate-270 on the substrate (Scheme 6). Differences in the acidity dependences of the catalytic rate constant with the metal ions Zn + (p STa 6.1) and Co +-(pATa 4.9) suggest that ionization of the metal-bound water molecule occurs and is involved in the decay of the anhydride. The catalytic rate constant shows an isotope effect in DgO. 

The metal ions arise from the ionization of the metal salt whose (monovalent) anion is represented by The hydroxyl ions OH originate... 

The difference of potential between a metal electrode and a solution of one of its salts may be regarded as due to the passage into solution and ionization of the metal (in which case the electrode becomes negative to the solution), or to the discharge of the metal ions in the solution at the electrode (in which case the electrode becomes positive to the solution). 

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