Oxygen-donors

Multidentate ligands contain more than two coordinating atoms per molecule, e.g. 1,2-diaminoethanetetra-acetic acid (ethylenediaminetetra-acetic acid, EDTA),f which has two donor nitrogen atoms and four donor oxygen atoms in the molecule, can be hexadentate. 

Those in which solvent molecules are directly involved in formation of the ion association complex. Most of the solvents (ethers, esters, ketones and alcohols) which participate in this way contain donor oxygen atoms and the coordinating ability of the solvent is of vital significance. The coordinated solvent molecules facilitate the solvent extraction of salts such as chlorides and nitrates by contributing both to the size of the cation and the resemblance of the complex to the solvent. 

Discussion. Molybdenum(VI) in acid solution when treated with tin(II) chloride [best in the presence of a little iron(II) ion] is converted largely into molybdenum(V) this forms a complex with thiocyanate ion, probably largely Mo(SCN)5, which is red in colour. The latter may be extracted with solvents possessing donor oxygen atoms (3-methylbutanol is preferred). The colour depends upon the acid concentration (optimum concentration 1M) and the concentration of the thiocyanate ion (1 per cent, but colour intensity is constant in the range 2-10 per cent) it is little influenced by excess of tin(II) chloride. The molybdenum complex has maximum absorption at 465 nm. 

Y, then C-OR bond breaking should be even more dependent on, and thus sensitive to, the orientation of the lone pairs on the single donor oxygen of [91], This conclusion is relevant to the reactions of glycosides, and has important implications for the enzyme-catalysed reactions at their anomeric centres. 

Consequently, the red-complex is extracted with either solvents possessing donor oxygen atoms, such as 3-methyl butanol. However, Mo (VI) may also be extracted with diethyl ether-an oxygenated solvent, because it yields the maximum percentage extractive with 7.0 M NH4 SCN as could be seen from the following Table 27.2. 

Cyanobacteria H2O (donor) oxygenic Ferric oxide and hydroxide precipitation due to high ambient O2. 

Group VI Donors. Oxygen donor ligands. A series of unsymmetrical tris-(P-diketonato)M " complexes (17) has been investigated in order to establish CIS—trans isomer distributions, and relative rates of isomerization. Included in this study was the preparation and separation of the geometric isomers of [Ru(tfac)3] and [Ru(bzac)3] (tfac = trifluoroacetylacetone, bzac = benzoyl-acetylacetone). In weakly polar media, the trans-isomer of [Ru(tfac)3] was found to be more stable, whereas the isomer distribution of similar complexes with R, R = alkyl or Ph, is statistical. ... 

Group VI Donors. Oxygen donor ligands. A new and more successful preparation of CIS- and tra s-K[Rh(ox)2(H20)2] has been reported, via the chromatographic separation of the acid hydrolysis products from Kj[Rh(ox)3],4j-H20. The u.v.-visible spectra of these complexes cast doubts on the purity of the samples previously described. An interesting feature of Rh -oxalate chemistry is the assertion that K3[Rh(ox)3],4 H20 actually exists as the partly unidentate K6[Rh(ox)3][Rh(ox)2(C204H)(OH)],8H20. This has now... 

Group VI Donors. Oxygen and sulphur donor ligands. Oxidative addition of tetrachloro-l,2-benzoquinone to rrans-[Ir(CO)Cl(PR3)2] (R3 — Ph3 or Ph2Me) has been shown to give the Ir ° products [Ir(02CgCl4)(C0)Cl(PR3)2], whose structures (45) were confirmed from far-i.r. and H n.m.r. data. Comparison... 

Group VI Donors. Oxygen and mixed oxygen-nitrogen donor ligands. A more convenient synthesis has been reported for the chiral complex [Pd(tfacCam)2] (52), involving the reaction of Ba(tfacCam)2 with PdCl2- ... 

Manganese(II) has been commonly employed as a templating metal ion for the synthesis of a wide range of other mixed donor (oxygen/nitrogen) Schiff base macrocycles (and/or their imine-reduced derivatives). 

The oxidative deamination mediated by 3,5-di-t-butyl-o-quinone [257] could very well involve aC- 0 1,5-sigmatropic hydrogen shift within the Schiff base network. This process in essence accomplishes oxidation of the amine and reduction of the quinone. The interesting point is the strong donor oxygen forces the nitrogen atom into an acceptor role during the reaction. 

Although the methyl groups in acetylacetonate complexes retard some reactions by steric hindrance, they provide some electronic enhancement in reactions with electrophiles and furthermore protect the donor oxygen atoms from electrophilic attack. These properties have been discerned by a comparison of the numerous reactions of acetylacetone complexes with the relatively few successful reactions of complexes of formylacetone and malondialdehyde. 

The tendency to combine more strongly with sulfur than with oxygen (as instanced by the precipitation of many sulfides from aqueous solutions) is characteristic of many metals and can be explained theoretically.17 It could therefore be expected that chelate complexes of familiar ligands with a donor oxygen atom replaced by a donor sulfur would be more stable and more selective. 

It is interesting to note that condensed phosphate ligands such as tripolyphosphate (TPP), ATP, and ADP contain negative donor oxygens that are harder bases than those of the phosphonates, and have characteristically different metal ion affinities. The stabilities of the alkaline earth chelates of these ligands are... 

Triorganyltin halides and pseudohalides form stable five-coordinate adducts with the donor oxygen atom of a strong ligand, such as C=0 (Table 23), P=0 (Table 24), S=0 (Table 25), N=0 (Table 26) and As=0 (Table 27), which have almost TBP geometry at tin. 

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