Mixed donor number

Thioether ligand complexes are not very common, however, studies since the mid 1990s have dramatically increased the number of structurally characterized examples. Almost all of these compounds are with chelate or macrocyclic ligands that will stabilize thioether coordination. Mixed donor multidentate ligands containing thioether donors will be discussed in Section 6.8.11. 

The zinc bis(tetraseleno) anion, [Zn(Se4)2]2-, has been crystallized with a number of cations, synthesized by a variety of methods, and its reactivity studied.581-584 The compound (hexaseleno) (tetraseleno)zinc (64) was synthesized from zinc acetate in the presence of lithium polyselenide and structurally characterized, demonstrating seven-membered and flve-membered ZnSen rings.585 Mixed donor neutral monomers have also been formed with imidazole A-donor ligands, ZnSe4 (A-methylimidazole)2.553... 

There are a number of mixed-donor tripodal ligand systems which have been characterized with... 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

A vast number of derivatives of these general types have been prepared by similar routes for catalytic applications, and at this point we can do no more than provide a series of recent references some have P-donor ligands [24], some have N-heterocyclic carbenes [25], and others have mixed donors [26]. 

Mixed donor macrocycles have been employed in a number of applications involving the separation or analysis of manganesetll). These include examples of use of such a ligand as the extractant in solvent extraction processes " and as the ionophore in membrane transport studies. 

The acid-base properties of a mixed solvent is also an important factor influencing the behavior of solutes. Thus, the parameters of the acidity and basicity of mixed solvents have been studied to some extent [35], Figure 2.10 shows the donor numbers of mixtures of nitromethane and other organic solvents. Because ni-tromethane has very weak basicity (DN= 2.7), the addition of small amounts of basic solvents (HMPA, DMSO, pyridine) increase the donor number remarkably. 

The number of nickel(U) complexes with mono-, bi- and poly-dentate ligands containing tertiary phosphines as a donor group is very large and increases day by day while complexes with tertiary arsines are less numerous and those with stibines are rarer still. The number of nickel(II) complexes with mixed donor ligands containing N, O and S donor atoms besides P or As is also very large. 

A large number of nickel(II) complexes with bidentate tertiary phosphines and arsines have been prepared and characterized since the initial reports on o-phenylenebisdimethylarsine and 1,2-bisdiphenylphosphinoethane (Table 64 XVIII, III) by Chatt and Mann,1267 and Wymore and Bailar126 respectively. The most common diphosphines, diarsines, distibines and mixed donor ligands are collected in Table 64 and selected nickel(II) complexes are reported in Table 65. 

The template synthesis has also been successfully employed for the preparation of macrocycles containing mixed donor atoms. Examples which refer to tetra- and bexa-dentate ligands are given in Schemes 42, 47 and 50.2649,2653 2654,2658 Apart from the template synthesis a number of nickel macrocycles have been prepared by direct combination of the appropriate nickel(II) salt with the preformed macrocyclic ligand in alcoholic medium, often MeOH (see also Tables 103, 106-108). 

The unsymmetrical, mixed donor DMET has produced a number of superconducting salts [10]. DMET can be prepared in acceptable yield by way of a mixed coupling reaction [72]. Preparation of 30 and 10 has been discussed previously. 

Examples of the use of synthetic mixed donor macrocycles in heavy metal ion separations are found in the discrimination of silver from lead. A number of studies indicate that the inclusion of sulfur in macrocyclic sequestering agents shifts the discrimination to silver. An example of this is seen with (57) and (58). For the aza-oxa macrocycle (57) the log K is 5.9 for both silver and lead ions, while the thia-incorporated ligand (58) complexes silver more efficiently (log K = 9.9) compared to lead (log K = 5.7). ... 

A key reason for the predominance of mixed donor systems is that the common donor atoms are met in a number of... 

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