N- and O-donors

Mixed N- and O-donors. The N4.03-type ligand (7) has been used to prepare complexes with a number of first row transition metal(m) ions including Cr . The ligand is 

Tsuchiya, T. Ohki, A. Uehara, and E, Kyuno, Thermochim. Acta, 1975,12,413. 

Bator-Sawicka, G. Blotny, and J. Dobrowdski, Rocznik Chem., 1975,49, 829. 

The formation of chromium(iii) complexes of ethanolamine-NN-diacetic acid in aqueous solution has been investigated by potentiometric and colorimetric methods. A1 1 complex is found to be formed in the pH range 3—6. At pH 6 hydrolysis takes place. Isolation of mono-, di-, and hetero-nuclear Cr chelates of ttha (ttha = triethylaminetetra-aminehexa-acetic acid) has been accomplished. No evidence for exchange coupling was found for either the dinuclear complex or for the heteronuclear Cr, Cu complex, CrCu(Httha)2,7H20.  

A complex of formula [Cr(AEP)0H]2,4H20 (AEP = 2-aminoethyl phosphinic acid) has been prepared and characterized by spectroscopic and magnetic studies. A dimeric stereochemistry with two OH bridges is confirmed, with /i = 3.37 BM per Cr atom supporting this stereochemical assignment. The reaction of Cr(CO) with pyridine-2-carboxylic acid (picH) in boiling MeOH affords Cr(pic)3.  

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Glucose isomerase catalyzes the conversion of D-glucose to D-fructose and has also been used extensively on an industrial scale.1184 Some, but not all, enzymes of this family require Co specifically, while others can function with other divalent ions. Environmental and health issues limit the concentrations of Co in culture media during D-fructose production and other metal ions are being sought as substitutes. Although the active site structure remains unknown, EXAFS, optical and EPR spectroscopy has suggest a low-spin divalent Co ion, bound by N and O-donors only (no S-donors). 

As for V(III), trigonal prismatic complexes, and trigonally distorted octahedral complexes are not uncommon for V(IV) [56]. The ligand set exerts a stronger influence on the redox potentials, whether the coordination geometry is octahedral or trigonal prismatic, at least to a first approximation. A series of compounds made with tridentate and tetradentate ligands with N- and O-donor atoms such as the azophenol derivative shown in Fig. 8 has both reversible oxidations and reductions. 

The halogenoboranes, unlike BH3, form more stable complexes with N and O donors than with P and S donors (see Section 24.2.1 and Table 5). Especially stable complexes are formed with N donors pyridine-trifluoroborane for instance can be distilled at 300 °C without decomposition.64... 

Besides the complexes with the various Schiff bases discussed in Sections 50.5.8.1.i-iv and with amino acids (Section 50.5.8.4.ii), nickel(II) complexes containing N,0 chelates amount to hundreds. It is possible that molecules containing every conceivable bridging chain between the N and O donor atoms have been investigated as ligands towards nickel(II). Almost all of these complexes exhibit either square planar or octahedral coordination. 

H. Bidentate Anionic Ligands with C-, N- and O-Donor Groups. 243... 

Generally, H", the heavier halides, and ligands which can be described as C-, P- or S-donors tend to be soft N- and O-donors, and F, are characteristically hard bases. Small cations of high charge are the hardest acids. The softest acids are cations such as Ag+, Hg2+ and Au3+ lacking a noble gas configuration, they are quite polarisable. The principle which makes this classification useful is that hard acids and hard bases, or soft acids and soft bases, form the strongest complexes like tends to go with like . 

The utility of the concept may be illustrated by comparing the chemistries in the III oxidation state of cobalt, rhodium and iridium. Co3+ is classified as a relatively hard acid, and the very large number of Co(III) complexes mostly involve N- and O-donor ligands. Attempts to prepare Co(III) complexes with P- or 5-donor ligands often lead to reduction to... 

Crown-ethers with different numbers of N- and O-donor centers and cryptandes [ 1,450 452,565,568,571,572,769-772] ... 

Mixed N- and O-Donor Ligands. Spectrophotometric titration methods have been used to establish the existence and stoicheiometry of V111 complexes with alanine, a-aminobutyric acid, lysine, and glycylglycine pH measurements showed that the amino-acid ligand is co-ordinated in the anion form.385... 

Mixed donor ligands. Thermodynamic parameters have been evaluated for the interaction of asparaginate with Fe2+ in aqueous solution at 25°C. On the basis of the results it is calculated that quite a large proportion of asparaginate in blood plasma may be complexed to iron(u) as well as to the expected copper(n).93 1.10-Phenanthro-line /V-oxide (phenNO) forms the complex [Fe(phenN0)3](C104)2 in which the ligands chelate by N- and O-donor atoms.96... 

Although macrocyclic receptors containing N and O donor atoms are suitable for detection of alkali metal cations, the detection of alkali earth cations required application of chelating receptors based on amino acids with EDTA-like spatial arrangement, eg bis(o-amino-phenoxy)-ethane-A, N, N, A -tetraacetic acid (BAPTA) [9,12], The most common calcium PET sensors are shown in Figure 16.6. 

This section is constructed to deal firstly with the group of ligands which possess potential N and O donors which cannot both bind to the one Mn atom. The coverage will then extend, with increasing ligand denticity, to deal with ligands that can potentially bind more than one type of donor atom to the one Mn atom. 

There is even less variety in the known chemistry of the chloro compounds because of their lower redox stability.523 Although MnCl is stable only below — 40°C, apparently decomposing through a disproportionation reaction,623 the oxidation state is stabilized with other ligands. Thus MnCl3 is more robust in donor solvents, undoubtedly as species like [MnCl3L3], and compounds of this type are well established for both N and O donors (Sections 41.4.2 and 41.4.3.6). There is also a series of pyridine-JV-oxide compounds (Section 41.4.3.6) MnCl3L2 which may well be five-coordinate. 

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