Donor number affinity

Donor numbers are considered as semiquantitative measures of solute/EPD solvent interactions, and are particularly useful in the prediction of other EPD/EPA interactions in coordination chemistry. Numerous examples of the application of donor numbers have been given by Gutmann [26, 27, 30] cf. also [113, 133]. It has been shown that donor number correlations are parallel with correlations based on the highest occupied molecular orbital (HOMO) eigenvalues of EPD solvent molecules [139], For non-HBD solvents, a fair correlation has been obtained between their donor numbers and their gas-phase proton affinities FA, indicating that the DN values do indeed reflect the intrinsic molecular properties of EPD solvents [140]. 

Information about the relative strength of the interaction between terbium and aqueous and non-aqueous solvents was obtained by Batyaev et al. (1975). Terbium perchlorate solutions (0.0036 M) in water, deuterated water, pyridine-water, n-propanol-water, acetonitrile-water, DMF-water, and methanol were studied by relaxation spectroscopy. An affinity series could be established, which is parallel to the donor number of the solvents ... 

Among numerous thermodynamic measurements on the complexes of covalent metal halides, antimony pentachloride was chosen by Gutmann (1966-1968) [78] as the reference Lewis acid for constructing an SbCls affinity scale and developing the donor number concept. This scale is critically presented in Chapter 2. 

The first calorimetric measurements on the reaction of SbCb with Lewis bases in solution seem to have been made in 1963 by Olofsson [1], Later, this author published a series of papers between 1963 and 1973 on the enthalpy of complexation of SbCls with numerous carbonyl bases [2-11], and also a few ethers [11, 12], methanol [12], water [13] and nitrobenzene [11], Gutmann extended this series to a host of different Lewis bases [14,15] and proposed, in 1966, the concept of donor number (DN) [16-18] to express quantitatively the Lewis basicity of soivents. Although the DN scale has been proposed and extensively used [19-21] as a solvent parameter, it relies on measurements made on dilute solutions of bases. It is, therefore, a solute scale and not a solvent scale of Lewis affinity. 

Lewis Basicity and Affinity Scales 2.4 The Donor Number Scale Data... 

A strong affinity of solv for M as compared to that of solv is one of the main driving forces for this process. Such ligand substitution is common when the donor number of solv is higher than that of solv. Thus, synthetic methods... 

The chemistry of Th(IV) has expanded greatly since the mid-1980s (14,28,29). Being a hard metal ion, Th(IV) has the greatest affinity for hard donors such as N, O, and light haUdes such as F and CF. Coordination complexes that are common for the t7-block elements have been studied for thorium. These complexes exhibit coordination numbers ranging from 4 to 11. 

Since the energy of the transfer band is determined by the difference between the donor ionization potential and the acceptor electron affinity, this fact points to the increase of the PCS ionization potential with decreasing conjugation efficiency. Therefore, the location of the transfer band of the molecular complexes of an acceptor and various PCSs can serve as a criterion for the conjugation efficiency in the latter. In Refs.267 - 272) the data for a number of molecular complexes are given, and the comparison with the electrical properties of the complexes is made. 

Ahrland et al. (1958) classified a number of Lewis acids as of (a) or (b) type based on the relative affinities for various ions of the ligand atoms. The sequence of stability of complexes is different for classes (a) and (b). With acceptor metal ions of class (a), the affinities of the halide ions lie in the sequence F > Cl > Br > I , whereas with class (b), the sequence is F < Cl" < Br < I . Pearson (1963, 1968) classified acids and bases as hard (class (a)), soft (class (b)) and borderline (Table 1.23). Class (a) acids prefer to link with hard bases, whereas class (b) acids prefer soft bases. Yamada and Tanaka (1975) proposed a softness parameter of metal ions, on the basis of the parameters En (electron donor constant) and H (basicity constant) given by Edwards (1954) (Table 1.24). The softness parameter a is given by a/ a - - P), where a and p are constants characteristic of metal ions. 

One way to reduce the number of independent variables in the FRET-adjusted spectral equation is to use samples with a fixed donor-to-acceptor ratio. Under these conditions, the values of d and a are no longer independent, but rather the concentration of d is now a function of a and vice-versa. This approach is typical for the situation of FRET-based biosensor constructs. These sensors normally are designed to have a donor fluorophore attached to an acceptor by a domain whose structure is altered either as a result of a biological activity (such as proteolysis or phosphorylation), or by its interaction with a specific ligand with which it has high affinity. In general, FRET based biosensors have a stoichiometry of one... 

N-heterocycles are a class of neutral ligands with strong coordination affinity to many metal ions. Since a number of neutral N-donors ligands are available, a wide range of oxo-centered triruthenium complexes with various N-heterocyclic ligands have been prepared through axial ligand substitution. By judicious selection of the N-heterocyclic type and modification of the substituents with different electronic and steric effects, the electronic, redox, and spectroscopic properties in these oxo-centered triruthenium derivatives are controllable. 

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