Reaction of Ni with

Guided ion beam tandem mass spectrometry has also been employed to study the reaction of Ni+ with CS2 and COS.2410 The ground state ion Ni+ undergoes endothermic reaction to form NiS+ in both cases, as well as NiCS+ and NiCO+, respectively. Threshold values for the reactions and bond dissociation energies for the products have been determined. 

Figure 3. Variation with relative kinetic energy of cross sections for reaction of Ni+ with HD. Data from reference 24.

The relaxation approach has played an important role in our understanding of the mechanisms of complex formation in solution (Chap. 4) 39,i4o -pjjg qj computer programs has now eased the study of multiple equilibria. For example, four separate relaxation effects with t s ranging from 100 xs to 35 ms are observed in a temperature-jump study of the reactions of Ni with flavin adenine dinucleotide (fad) (Eqn. (8.121)). The complex relaxation... 

AK values for reactions of Ni + with neutral ligands range from -1-5 to -l-ll cm rnol" . Ref. 14. 

The reaction of Ni " with produces Ni, which is a strong reductant... 

The reaction of Ni " with [e, ]" produces Ni, which is a strong reductant capable of reacting rapidly with organic and inorganic oxidants. The reaction of Ni" " with Oj occurs via the formation of [NiOj]+. The Ni" " ion reacts with a-hy-droxyalkyl radicals via the formation of a Ni—C bond, e.g. ... 

Systems in which specific solvent structural effects do not seem to affect kinetic patterns include the reactions of Ni + with malonate in aqueous d-ftuc-tose, some substitutions at [Fe(CN)5L] anions, and aquation of the [Cr(NH3)sBr] + cation in several series of alcohol-water mixtures. Deviations from a newly proposed correlation of rates with solvent DN and AN values (c/. above, refs. 24 and 25) have been used as a probe for specific solvent structural effects. - Ethylene carbonate and propylene carbonate have no structure... 

In most of the investigations mentioned so far in this section involving solvent mixtures it is likely that the primary solvation shell does not vary with solvent composition. However, there are occasions when variation of reactivity with solvent mixture composition is attributed to changes in primary solvation shell composition, as in the case of reaction of Ni + with ammonia in aqueous methanol. In the reaction of Be + with sulphate in aqueous DMSO, there is strong n.m.r. evidence for variation in primary solvation shell composition. In the reaction of Co with tetraphenylporphine in acetic acid-water the kinetics also reflect the presence of varying amounts of mixed solvates. By way of contrast, in reactions of copper(ii) with polythiaethers in methanol-water mixtures only Cuaq + reacts mixed solvates are claimed to be of negligible reactivity. In the reaction of chromium(iii) with edta in methanol- and ethanol-water mixtures, variation in pK for the Cr + has an effect on the formation rates, but the individual rate constants for the reactions of Cr + and of CrOH + with the ligand seem to be practically independent of solvent composition. ... 

It is of interest now to consider the kinetics of complex formation (kf) and dissociation (kd) of chelate, macrocyclic, and cryptate complexes and how these are related to the type of ligand stmcture. Table 10 lists kf and kj valnes for chelating ( 1-3), macrocyclic ( 4 and 5), and cryptand ( 6-8) ligands and the appropriate reference compounds. For the chelate effect, the reactions of Ni " with py, bipy, and terpy show very little difference in kf values. On the other hand, the valnes of kj decrease by factors of 2 x 10 and 2 X 10, for bipy and terpy, respectively. A similar effect is seen in a comparison of the reactions of Cn + ion with the thioether macrocycle [14]aneS4 (ane denoting a saturated carbon macrocycle and S4 (he four sulfur donor atoms) and its acyclic... 

The authors are able to show that the same scheme holds for the reaction of Ni + with various simple amino-acids but point out that it is necessary, for a complete... 

The volume of activation for the reaction of Ni + with (6) in water is 12.2 cm mol at 25 °C, a value which is consistent with rate-limiting replacement of the first... 

The relaxation trace of the complexation reaction of Ni with pyridine-2-azo-p-dimethylaniline (PADA), shown in Fig. 2, was achieved by applying the SF mode. The measured time constant is in good agreement with the literature (3). 

In the chlorine poisoning, the reaction of Ni with chlorine is crucial to understand the poisoning mechanism. According to Haga et al. [18] the formation of NiCl2 may be described by reaction (6.1) ... 

The rate constants for the formation of 1 1 complexes of some dialkyl-2,2 -bipyridyl-5,5 -dicarboxylates with Ni in methanol have been corre-lated with the Taft modification of the Hammett equation this result is consistent with there being an inductive effect from the alkyl groups. Comparison of the rate constants and activation parameters for the reaction of Ni " with 2,6,9,13-tetraazatetradecane, 1,4,8,11-tetraazacyclo-tetradecane, and N,N, N",N" -tetTamethyl-1,4,8,11 -tetraazacyclo-... 

Estimates of 8 x°(Fe ) can also be made in a very similar manner from FeCbipy) " stability constants/ 2,2 -bipyridyl solubilities/ and published estimates for 8 x°[Fe(bipy)3 ]/ If we now make the very reasonable assumption that 8 fx (Ni ) = 8 x°(Fe ) we can analyze solvent effects on reactivity into initial state and transition state contributions for formation reactions of Ni ". The result of such an analysis for the reaction of Ni " with 2,2 -bipyridyl in methanol + water mixtures is shown in Figure 5.3. The conclusion reached here, that initial state effects are rather larger than transition state effects, is the same as that reached by Wells for this reaction. The differences between these are somewhat larger in Wells s treatment, owing to his assumption of a D rather than an Id mechanism. One feature of Figure 5.3 which does not emerge from Wells s approach is the dominant role played by the 2,2 -bipyridyl. It is... 

Variations in the formation and dissociation rate constants for nickel(ii) malonate in water-dioxan mixtures seem to be primarily due to changes in the ion-pair formation constant, which is very sensitive to the dielectric of the solvent, and reference has already been made (Table 3) to the stabilization of the outer-sphere complex noted in the reaction of Ni with a series of ligands in DMF. The low values of kt for the reaction of Ni with (1), (5), and (6) in DMSO (Table 4) are interpreted in terms of steric control. 

Rate constants and activation parameters have been reported " for the reactions of Ni + with 4-phenylpyridine, bipy, phen, and terpy in propan-l-ol, propan-2-ol, and isobutyl cyanide as solvents. The donor strength of the solvent appears to be of particular importance in the formation as well as the dissociation reaction (see also ref. 8 and Vol. 4, p. 211). It has been shown by n.m.r. measurements that, in DMF-methanol mixtures, nickel(n) ions are preferentially solvated by two DMFmolecules the remaining solvent molecules in the inner sphere are then distributed on a statistical basis according to the composition of the bulk solvent. The methanol exchange rate at Ni + is enhanced by co-ordinated DMF, logA ex ° being linearly... 

Solvent Structure. There has been some discussion of the importance of solvent structure in kinetics, for example in connection with aquation of cobalt(m) complexes in binary aqueous mixtures. There are difficulties in squaring the kinetic parameters for dimethylformamide and for dimethyl sulphoxide exchange at iron(u) with Bennetto and Caldin s model of solvent structural effects, but this model proved useful in discussion of the aquation of [Co(NH3)s(DMSO)] + in binary aqueous mixtures. Bulky hydrophobic groups in solvent molecules have an effect on solvent structure which is reflected in the kinetics of complex formation. - For dissociative solvent exchange at some M + ions, activation enthalpies appear to be determined by the solvation enthalpy of the metal ion and the solvent structure as manifested in its enthalpy of vaporization. In the reaction of Ni + with malonate, the range of solvent variation of activation parameters is comparable with their likely errors, preventing the authors from discussing their results in terms of Bennetto and Caldin s theories. ... 

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