O-donor complexes

A series of oxovanadium(iv) carboxylates V0(RC02)2 (RCO2 = acetate, propionate, butyrate, isobutyrate, valerate, pivalate, phenylacetate, benzoate, or w-chlorobenzoate) have been prepared by the reaction of freshly prepared hydrated V2O4 with a mixture of the corresponding acid and anhydride in toluene or DMF solution, and/or by the reaction of VOCI2 and the corresponding carboxylic acid in aqueous solution. I.r., electronic, and e.s.r. spectra 

The stepwise stability constants for V complexes with glutamic, aspartic, W -ethylenediaminedisuccinic, and W -ethylenediamine-bis-(a-glutaric acid) have been reported.The 1 1 oxovanadium(iv) complex of 5-nitrosalicylic acid has been characterized = 710 nm), and the mixed species formed between vanadium(iv) with protocatechuic acid (H3L ) or gallic acid (H L ) and 4-aminoantipyrine (aant) have been identified spectroscopically as the 1 1 1 and 1 2 2 HL (HL ) aant complexes. The species present in solutions of and tartaric acid below pH 2 have been identified as [VO- 

Sala-Pala and J. E. Guerchais, Bull. Soc. chim. France, 1971, 2444. 

A new class of crystalline vanadium(iv) compounds, salts which contain the golden-yellow [V(OR)Cl5] ion, have been prepared by addition of one mole of R OH (R = Me, Et, Pr, or Bu) to a slurry of (NR ) or (pyH )[VClg] in MeCN-Et20. Similar attempts to prepare [V(OR)2Cl4] , however, were unsuccessful. Magnetic moments and e.s.r., electronic, and i.r. spectra of these pentachloroalkoxovanadates are consistent with their proposed formulation. 

VOXj (X = Cl, Br, or I) react with (Pr 0)2MePO to form [V0 0(0)PMe-(OPr ) 2], which appears to be polymeric. The low steric interactions of pyridine 1-oxide and 4-methylpyridine 1-oxide (L ), combined with the weak nucleophilicity of the tetrafluoroborate anion, allow the formation of the 

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The O-donor complexes of Tc(V) exhibit moderate and differential stability in aqueous solution. In the presence of reducing agents, such as stannous chloride, they are reduced to mainly undefined products of Tc in a lower oxidation state. However, at the low technetium concentration of "mTc that is used in nuclear medicine, the rate of the reduction process is very low. This makes it possible to prepare Tc(V) radiopharmaceuticals with O-donor ligands by the usual procedure, in which an excess of reducing agent over technetium is unavoidably used. The Tc(V) complexes also tend either to be easily oxidized or to disproportionate [23],... 

O-donor complexes that are currently used as Tc(V) precursors in the chemical and radiopharmaceutical synthesis are listed in Table 1. 

Hathaway and Hodgson708 have discussed the results of structural studies on a wide range of N- or O-donor complexes in terms of the various distorted geometries possible and have shown that the degree of tetragonality (equal to mean in-plane Cu—L bond length divided by mean out-of-plane Cu—L) varies from ca. 0.6 to 0.9. A correlation also exists between the band maxima of the electronic spectra and the square of the frequency of the asymmetric v(Cu—N) in Cu(NH3)4X2 and Cu(NH3)5X2, and possibly also with the Cu—N bond lengths.709... 

However, in contrast to arsenic, antimony compounds remain of medicinal importance, particularly in the treatment of various parasitic infections including leishmaniasis, schistosomiasis, and trypanosomasis. Coordination compounds used include the sodium or potassium antimony tartrates and substituted catecholate complexes, which are O-donor complexes, whilst S-donors are utilized in 2,3-dithiosuccinate derivatives.While the mode of action is unclear in many cases, the attraction of these compounds, in addition to their clinical effectiveness, is their simplicity of manufacture and low cost. 

Complexes of cobalt(III) with O-donor ligands are generally less stable than those with Af-donors although the dark-green [Co(acac)3] and M iCo-( 204)3] complexes, formed from the chelating ligands acetylacetonate and oxalate, are stable. Other carboxylato complexes such as those of... 

Complexes of and The effect of complexation on the splitting of d orbitals is much greater in the case of second- and third-than for first-row transition elements, and the associated effects already noted for Ni are even more marked for Pd and Pi as a result, their complexes are, with rare exceptions, diamagnetic and the vast majority are planar also. Not many complexes are formed with O-donor ligands but, of the few that arc, [M(H20)4] ions, and the polymeric anhydrous acetates [Pd(02CMe)2l3 and [Pt(02CMc)2]4 (Fig. 27.10), are the most... 

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Copper(II) also forms stable complexes with O-donor ligands. In addition to the hexaaquo ion, the square planar /3-diketonates such as [Cu(acac)2l (which can be precipitated from aqueous solution and recrystallized from non-aqueous solvents) are well known, and tartrate complexes are used in Fehling s test (p. 1181). 

A wide variety of complexes are formed by both metals in the +2 oxidation state indeed, it is the most important one for palladium. The complexes can be cationic, neutral or anionic. Both Pd2+ and Pt2+ are soft acids so that many stable complexes are formed with S or P as donor atoms but few with O-donors, though there are important ammines. There are pronounced similarities between corresponding palladium and platinum complexes the latter are more studied (and less labile). 

Complexes of O-donors are relatively rare, explicable by the soft nature of the divalent ions. A telling indication is that sulphoxide ligands will only bind through O if steric effects make S-bonding impractical. The most important complexes are diketonates and carboxylates (for the aqua ions see section 3.5). 

Apart from Au(N03)4, relatively few complexes of gold(III), and only those with O-donors, have been examined. Two that demonstrate the preference of gold(III) for square planar coordination are SrAu2(MeCOO)8 and SrAu2(OH)8 in the latter Au(OH)4 has Au-O 1.98 A [117]. 

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