Solvents donor number

The complexes [Ru(NH3)5(26)] and [Ru(NH3)5(27)] + have been prepared and isolated as PFg salts. Oxidation by ferrocenium ion occurs with the redox change being centered on Ru. The solvent has a significant effect on the difference between Pi/2°(Fe3+/Fe2+) and Pi/2°(Ru +/Ru2+) and there is a linear relationship between this A and the Gutmarm solvent donor number. ... 

FIGURE 1. Dependence of the log of conductivity of 0.1 M solutions of le measured at 20 °C on the solvent donor number DN. The correlation coefficient is given... 

Owing to the presence of the amine and cyanide ligands, known to give rise to specific donor-acceptor interaction with solvents [126-130], an interesting solvatochromic behavior is observed for these species. For complex 1 the spectral changes are dominated by amine interactions with the solvents as shown by the linear correlation of the solvent donor number [131] with the IT band maxima and with the half-wave potential of the ruthenium amine moiety. 

FIGURE 3. 29Si chemical shifts of trimethylsilanol vs. solvent donor numbers, DN. Reproduced by permission of The Chemical Society of Japan from Reference 44... 

In asymmetric complexes of the type [(bpy)2RuCl(pi-pyz)Ru-(NH3)4L]4+, studies (94) revealed that there is a solvent donor-number (DN)-dependent contribution to the Frank-Condon barrier of approximately 0.006 eV/DN, which completely overwhelms the dielectric-continuum-theory-derived (l/Dop-l/Ds) solvent dependence typically observed in symmetrical dimers. In this case, variations in MMCT Eop with solvent give linear correlations when plotted against solvent dependent AEm, the difference in potential between the two ruthenium(III/II) couples, as shown in Fig. 10. The microscopic origin of this solvent effect was described by Curtis, Sullivan, and Meyer (122) in their study of solvatochromism in the charge transfer transitions of mononuclear Ru(II) and Ru(III) ammine complexes. The dependence... 

The solvent-induced change in rate is, however, much larger than expected from the relatively small difference in polarity between nitromethane and hexamethylphos-phoric triamide. This, together with the correlation between rate decrease and increase in the solvent donor number DN cf. Table 2-3 in Section 2.2.6), suggests that specific solvation and stabilization of the diazonium ion by EPD solvents play a dominant role in the reaction (5-27). Very likely, formation of an EPD/EPA complex between the reactants in a rapid preequilibrium step precedes the rate-controlHng first step [504, 792],... 

DN solvent donor number (Gutmann) [= -AiT(D—SbCls)] kcal mol ... 

Many groups have investigated the suitability of various solvents for use in LM systems and have attempted to describe the relationship between solvent characteristics and transport properties [93-96]. Of all solvent properties, dielectric constant seems to be most predictable in its effect on transport [92]. For solvents, such as the halocarbons, transport usually decreases with increasing dielectric constants [93]. Figure 2.10 shows this trend for alkali metals binding by dicyclohexano-18-crown-6 in a number of alcohols. This trend holds true for many simple systems, but it breaks down under more complex conditions. Solvent donor number, molecule size, solvent viscosity, carrier solubility in the solvent, permanent and induced dipole moments, and heats of vaporization are important [94]. 

Figure 4.15 Expansion along the perpendicular laminating direction of Nafion (Li+ form) versus donor number (DN) of mixed solvents. (Donor number is defined as AHosbCh with D + SbCl5 D.SbCls in 1,2-dichloroethane where D is the solvent.62) (A) water-2-propanol ( ) water-ethanol ( ) water-forma-mide (X) cyclohexanone-2-propanol.

The solvent donor number, first defined by Gutman [4] and abbreviated to DN, is a system specific, but quantitative measure of the ability of a substance to act as an electron pair donor. In its original form it is defined as the negative of the heat of reaction for the formation of the 1 1 adduct between the test substance and antimony pentachloride, measured in 1,2-dichloroethane as solvent (equation 12.2). 

The redox reactions of (TPP)CrCl04, (TPP)CrCl04(L) and [(TPP)Cr(L)2]+ were also investigated and correlations between Ei/2 for reduction of (TPP)CrCl04 and the Gutman solvent donor number [154], as well as between 1/2 for reduction of (TPP)CrCl04 or (TPP)Cr and the solvent dielectric constant, were also examined [98]. 

The half-wave potentials for the Fe(III)/ Fe(II) reaction of (TPP)FeX varied little as a function of the counteranion in DMSO or Py, and this was accounted for by a displacement of the halide axial ligand by a bound solvent molecule leading to [(TPP)Fe" (S)2]+ and (TPP)Fe"(S)2 in solution, where S = DMSO or Py. The effect of solvation on the Fe(III)/Fe(II) reaction of (TPP)FeX was quantitated by Bottom-ley and Radish who correlated E1/2 values for reduction with the Gutmann solvent donor number [187]. Half-wave potentials... 

The standard, heterogenous rate constants, ks, of the Ni(II)/Ni(III) redox couple in complexes 1 and 2 were determinated in such solvents as ACN, H2O, AC, DMF, and DMSO, by Nicholson s method for the quasi-reversible processes. For complex 1 the values of ks were nearly independent on the NaC104 concentration (0.1-lM). This independence is extremly important because the measured ks values can be discussed as "true" values. We suppose that the same is valid for complex 2. For both.complexes the linear relation between the Inks and the solvent donor number (DN) has been found (Fig.6) what can be explained by the inner solvation shell effect. 

The CV/potential step analysis was carried out in a series of other solvents. The variation in the reduction potential (measured against a ferrocene standard in each solvent) was shown to be best correlated with the solvent donor number (rather than the dielectric constant), indicating a specific interaction of the solvent with the nitronium ion. The kinetics of the electrode process were much... 

Solvent properties at 25"C Solvent Donor number Dielectric constant... 

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