Halo complexes

Addition of halide ions to aqueous copper(II) solutions can give a variety of halo-complexes for example [CuCl4] (yellow square-planar, but in crystals with large cations becomes a flattened tetrahedron) [CuClj] (red, units linked together in crystals to give tetrahedral or distorted octahedral coordination around each copper). 

The complex anion [ScFe] " has already been mentioned and, while there is a fairly extensive series of halo complexes with a... 

In addition to the aqua ion, a range of mixed aquo-halo complexes are known [38], including all 10 isomers of Rh(H20)6 VC1(X3 x)+. Synthetic entry into the series is possible from either end, the determining factor being the labilizing effect of chloride ... 

Although Pb(IV) is sufficiently strong an oxidant to oxidise halides, no kinetic data are available. Complexes of Pt(IV) and Au(III) oxidise iodide and thiocyanate ions but the other oxidants are weaker and form stable halo-complexes. However, some simple molecules such as hypophosphorous acid, carbon monoxide and molecular hydrogen are oxidised by the weaker members. 

A relationship between the intramolecular metal-metal separation and metal-metal force constants (estimated from the metal-metal stretching frequencies) was also determined for the halo complexes as ... 

The technique of performing halide abstraction via interaction of a metal halo complex with a silverd), thallium(I), or nitrosonium salt (see ref. 142, for discussion) has proved useful in the isolation of many novel sulfoxide complexes. Thus, [Pd(S-Me2S0)2(0-Me2S0)2]-... 

Solvato complexes of platinum(II) of the type fraws-[PtY(solvent)L2]+ (Y = hydride, alkyl, or aryl solvent = alcohol or ketone L = tertiary phosphine or arsine) have been known since 1961.1 They are obtained by halogen abstraction from the corresponding halo complexes tran.s-[PtXYL2] in the presence of the desired solvent.2 The methanol complex is also rapidly and quantitatively formed when trans-[PtH(N03)(PEt3)2] is dissolved in this solvent.2... 

These compounds, together with the halo complexes described in the next section (39.2.7.5), form the bulk of the known complexes of tetrapositive lanthanides. 

With the exception of the neutral halo complexes, which are prepared by direct reaction of the halogen with the metal, and a number of complexes generated by the direct reaction of the metal with a strong acid, coordination complexes of Os are prepared directly or indirectly from [0s04] (2). The latter is a toxic, volatile solid, normally purchased in 1-g ampuls and opened within the reaction mixture contained in a fume hood to prevent escape of the toxic vapor (3) and loss of the reactant. It is also available as an aqueous solution of osmic acid, which is suitable for some reactions. 

Most halo complexes have been discussed in previous sections (Table XI). Table XII (239,268,323,400,403,476-499) summarizes studies on complexes that contain only halo ligands or halo/oxo complexes. 

Table 96 Bond Distances and Angles in some Halo Complexes of Nickel(II) ...

Since these substitution reactions follow a two-term rate law, it is clear that solvent effects are very significant. Poorly coordinating solvents are benzene, carbon tetrachloride and sterically hindered alcohols and strongly coordinating solvents are water, lower alcohols, DMF, DMSO, acetonitrile and nitromethane. The first-order rate constants are greater in DMSO than in water. Since the majority of precursor platinum complexes used in synthetic and mechanistic studies are halo complexes, the replacement of halide ligands by solvent and the reversibility of this reaction are important features of platinum halide chemistry. 

Oxygen-containing solvents such as water, alcohols or ethers are such poor donors that few complexes with palladium(II) have been isolated. The most important class of complexes of this type consists of those containing water, which are formed as intermediates in the substitution reactions of palladium(II) when carried out in aqueous solution. In these reactions their formation is in competition with the second order reaction of the complex with the incoming ligand. The aqua complexes can also be formed by reaction of halo complexes with silver salts (e.g. N03, C104, BF4) in water. These complexes are acidic, being in equilibrium with hydroxo complexes in neutral or basic media. 

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