Metallic diiodides

Lead Iodide. Lead diiodide, Pbl2, forms a powder of yellow hexagonal crystals some physical properties are given in Table 1. Lead diiodide is soluble in alkaUes and potassium iodide, and insoluble in alcohol. It is made by treating a water-soluble lead compound with hydroiodic acid or a soluble metal iodide. It is readily purified by recrystaUization in water. 

Compound 9 has been prepared by the latter authors using triethylene glycol diiodide and triethylene glycol diamine (see Eq. 4.11) and an alkali metal carbonate in acetonitrile solution. ... 

Of the anhydrous dihalides of iron the iodide is easily prepared from the elements but the others are best obtained by passing HX over heated iron. The white (or pale-green) difluoride has the rutile structure the pale-yellow dichloride the CdCl2 structure (based on cep anions, p. 1212) and the yellow-green dibromide and grey diiodide the Cdl2 structure (based on hep anions, p. 1212), in all of which the metal occupies octahedral sites. All these iron dihalides dissolve in water and form crystalline hydrates which may alternatively be obtained by dissolving metallic iron in the aqueous acid. 

The isomorphous diiodides of Ce, Pr and Gd stand apart from all the other, salt-like, dihalides. These three, like LaH, are notable for their metallic lustre and very high conductivities and are best formulated as (Ln ,2I",e", the electron being in a delocalized conduction band. Besides the dihalides, other reduced species have been obtained such as LnsCln (Ln = Sm, Gd, Ho). They have fluorite-related structures (p. 118) in which the anionic sublattice is partially rearranged to accommodate additional anions. 

Samarium and ytterbium metals dissolve in tetrahydrofuran (THF) solutions of diiodoethane to yield solutions of their diiodides, (JL) as... 

The direct reaction of zinc metal with organic iodides dates back to the work of Frankland(67). Several modifications have been suggested since that time to increase the reactivity of the metal. The majority of these modifications have employed zinc-copper couples(68-72), sodium-zinc alloys(73), or zinc-silver couples(77). Some recent work has indicated that certain zinc-copper couples will react with alkyl bromides to give modest yields of dialkylzinc compounds(74,73). However, all attempts to react zinc with aryl iodides or bromides have met with failure. The primary use of zinc couples has been in the Simmons-Smith reaction. This reaction has been primarily used with diiodomethane as 1,1-dibromides or longer chain diiodides have proven to be too unneactive even with the most reactive zinc couples. 

After several years of effort it has been possible to reproduce Schmidbaur fs addition of methyliodide W The problem appears to be that the methyliodide product is extremely photosensitive in solution. It decomposes with the production of methyl radicals and the ultimate formation of a mixture of the Au(I), and Au(II) diiodide products. The X-ray crystal structure of the methyliodide product is presented in Figure 5. Two features are to be noted. Firstly, the metal-metal distance lengthens only a small amount, 0.04A, but the Au iodide distance lengthens by approximately 0.20. The structural trans effect caused by the methyl group is not attenuated by the Au-Au bond. 

The effect of metal promoter species on the rate of carbonylation of [Ir(CO)2l3Me] was tested. Neutral ruthenium iodocarbonyl complexes such as [Ru(CO)3l2]2> [Ru(CO)4l2] or [Ru(CO)2l2]n were found to give substantial rate enhancements (by factors of 15-20 for a Ru Ir ratio of 1 13 at 93 °C, PhCl). Indium and gallium triiodides and zinc diiodide had comparable promotional effects. By contrast, addition of anionic ruthenium(II) species [Ru(CO)3I3] or [Ru(CO)2I4]2 did not lead to any appreciable promotion or inhibition. This behaviour indicates that the ability to accept an iodide ligand is a key property of the promoter. Indeed, it has been demonstrated that an iodide ligand can be transferred from [ Ir(C0)2l3Me] to neutral ruthenium or indium species [73,74],... 

The tetraiodide is slightly soluble in acetone and in ethanol (about 1 gm PoI4/liter) but is insoluble in dilute mineral acids and in ethers, aliphatic acids and hydrocarbons. It is slowly hydrolyzed by water and by concentrated alkali, the white product presumably being a basic iodide, and is decomposed by chlorine, hypochlorite, nitrite, and hot concentrated nitric acid. It does not react with ammonia gas but is reduced to the metal on heating in hydrogen sulfide. Suspensions of the tetraiodide in 0.1 N hydriodic acid are unaffected by hydrazine or sulfur dioxide, even on boiling, and there is no evidence for a diiodide. 

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