As O -Donor Ligands

P(0)- and As(0)- Donor Ligands. By comparison of the electronic spectral data for [Co(diars-02)2] 2( 104)4 [diars-02 = o-phenylenebis(dimethylarsineoxide)] with those for [Co(Me-Sal)2]2 the former was shown to be dimeric with each cobalt(ii) 

Ziegler, and I. Haiduc, Inorg. Chim. Acta, 1976,17, 13. 

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It is important to distinguish between outer-sphere and inner-sphere complexes. In inner-sphere complexes the surface hydroxyl groups act as o-donor ligands which increase the electron density of the coordinated metal ion. Cu(II) bound inner-... 

In this family of compounds, the N-donors come from unsaturated nitrogens in histidine amino acid residues, the S-donors come from methionine and cysteine residues, and the O-donors come from a carboxylic acid in the protein chain. Water, hydroxide and alkoxide oxygens are also employed as O-donor ligands. 

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... 

Palladium forms clusters of these types far less readily than nickel and platinum, unless they are stabilized by o-donor ligands such as phosphines. This may be due to the lower energy of Pd-Pd bonds as reflected in the sublimation energies, 427, 354 and 565 kJ mol for Ni, Pd and Pt. 

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). 

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 ligands. The pyroxene NaTiSi206, synthesized at high pressure (65 kbar) and temperature (1550 °C), is obtained as light-green crystals when quenched to room temperature. A-Ray studies showed that the crystals are of the NaM SijOg structural type, and the diffuse reflectance electronic spectrum confirmed that this is one of the few oxides known to contain Ti . ... 

Complexes with O-Donor Ligands. Zr0(N03)2,2Bu3P04, and HfOXj,-2BU3PO4 (X = NO, or Cl) have been identified as the species extracted by BU3PO4 from aqueous solutions acidified with The heats of forma-... 

The coordination chemistry of silver has historically been centred on the reaction of silver(I) ions with N-donor ligands and halides. However, an extensive chemistry now exists for P- and S-donor ligands, whilst for O-donor ligands only weak complexes are generally formed and they have been studied in much less detail. Based on the reactivity and stability of its coordination complexes, the silver(I) ion has been characterized as a class B or soft acid, for which the following stability order is observed N P>As>Sb 0 S Se Te FComparative studies between ligands with these donor atoms allowed the relative stability of silver bonds to be determined as P > S > N > O. 

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... 

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