Hydrides and halides

Carbonyl Halides and Hydrides. Fe2(CO) reacts with HBr or HI and Fe(CO)j with HBr under u.v. light to yield the halogeno-complexes [Fe(CO)3.X]2. Structure (16) is postulated, on the basis of the close similarity in i.r. spectra with those of [Fe(CO)3SR]2 complexes. 

The structure of the cluster compound [H2FeRu3(CO)j3] is based on a tetrahedron of metal atoms. There are three terminal CO groups bonded to each Ru, two terminal CO groups bonded to Fe, two asymmetric bridging CO groups bonded between Fe and Ru atoms, and it is suggested that the two 

The catenated hydrides of sulfur are known as the polysulfanes, of general formula H2S , n = 2—8. These consist of unbranched chains of sulfur atoms with hydrogen atoms at both ends. Some of these reactive yellow liquids can be prepared by heating sulfides with sulfur and then acidifying as shown in Equation (17.15), but a variety of more sophisticated methods was devised starting in the 1950s and include the treatment of the S Cl2 with HjS, as shown in Equation (17.16)  

Some Representative Catenated Oxoacids and Corresponding Anions 

The alkali metal halides are all high-melting, colourless crystalline solids which can be conveniently prepared by reaction of the appropriate hydroxide (MOH) or carbonate (M2CO3) with aqueous hydrohalic acid (HX), followed by recryslallization. Vast quantities of NaCl and KCl are available in nature and can be purihed if necessary by simple crystallization. The hydrides have already been discussed (p. 65). 

The Bom-Haber cycle is also useful in examining the possibility of forming alkali-metal halides of stoichiometry MX2- The dominant term will clearly be the very large second-stage 

M +(g)-(-e this is 7297kJ mol for Li but drops to 2255kJmol for Cs. The largest possible lattice energy to compensate for this would be obtained with the smallest halogen F and (making plausible assumptions on lattice structure and ionic radius) calculations indicate that CsF2 could indeed be formed exothermically from its elements  

However, the compound cannot be prepared because of the much greater enthalpy of formation of CsF which makes CSF2 unstable with respect to decomposition  

There is some evidence that Cs + can be formed by cyclic voltammetry of Cs+[OTeF5] in pure MeCN at the extremely high oxidizing potential of 3 V, and that Cs + might be stabilized by 18-crown-6 and cryptand (see pp. 96 and 97 for nomenclature). However, the isolation of pure compounds containing Cs + has so far not been reported. 

18-crown-6 and cryptand (see pp. 96 and 97 for nomenclature). However, the isolation of pure compounds containing Cs has so far not been reported. 

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Figure 4,4 Standard enthalpies of formation (A// and lattice energies (plotted as —t/O for alkali metal halides and hydrides.

Complexes with halide and hydride donor ligands 979... 

Both the halide and hydride etherate products of Eqs. (5) and (6) can be easily desolvated by heating to ca 90-120°C under reduced pressure [Eq. (7)]. The halide and hydride... 

TABLE 44. Diastereomeric ratios of the chelate tin halides and hydrides with a stereogenic tin atom containing a chiral tin atom and N-donor substituent... 

Perovskites — are a very large family of compounds with the crystal structure similar to that of (Ca, Sr) TiC>3 mineral, named after the Russian mineralogist T. A. Per-ovski (1792-1856). This structure is often called an inorganic chameleon due to the diversity of chemical compositions, structural modifications, and properties. Although most members of this family are oxidic compounds, some nitrides, carbides, halides, and hydrides also have this structure. 

Several of the trialkylaluminum and alkylaluminum halides and hydrides mentioned above are commercially available. Alkynyl, alkenyl, cyclopentadienyl, and aryl derivatives are, in general, not commercially available and must be synthesized for laboratory use. Alkynyl derivatives can be prepared by salt metathesis, as in the reaction of Et2AlCl with NaC=CEt to give Et2AlC=CEt. The acidity of terminal alkynes is sufficient for preparation of alkynyl aluminum compounds by alkane or hydrogen elimination upon reaction with a trialkylaluminum or an aluminum hydride (equation 17), respectively. TriaUcynyl aluminum compounds are typically isolated as Lewis base adducts to stabilize them against otherwise facile polymerization. Alkenyl compounds of aluminnm have similarly been prepared. 

Many phosphine-borane complexes Y3P BZ3 have been characterized. They include compouuds where Y = alkoxy, aUcyl, amino, halide, and hydride groups, and Z = alkyl, halide, and hydride. The stabilities of these complexes vary widely depending on the Lewis acidity and basicity of the boron and phosphorus moieties, respectively. The relative stabilities of Lewis acid-base complexes with BH3 are R3P > R3N > R3AS > R3Sb, but with BF3 the order is R3N > R3P > R3AS > RsSb. The stabihties of the borou halide complexes of phosphines follow the same order as the amine complexes BI3 > BBrs > BCI3 > BF3. 

Compounds with the sodium chloride structure range from the essentially ionic halides and hydrides of the alkali metals and the monoxides and monosulphides of Mg and the alkaline-earths, through ionic-covalent compounds such as transition-metal monoxides to the semi-metallic compounds of B subgroup metals such as PbTe, InSb, and SnAs, and the interstitial carbides and nitrides (Table 6.1). Unique and different distorted forms of the structure are adopted by the Group IIIB... 

These compounds are used as the precursors for MOCVD processes. Compared with halides and hydrides, the metal-organic compounds have much more complex structures because they contain large functional groups (e.g. allyl, butyl, methyl etc) and ligands (such as carbonyl, acetylacetonate, hexafluoroacetyl acetonate and so forth). Some representative examples are listed below [19,22] ... 

Table 1 Observed and calculated bond angles in some halides and hydrides of oxygen...

Similar addition reactions of molecular hydrogen have been shown for the iridium hydride complex, IrHCO(PPh3)2 (210a), and a detailed study of the reactions of this complex with acids and carbon monoxide allows a comparison between the halide- and hydride-carbonyl complexes (see Fig. 7b). 

A study of the complexes formed by alkali halides and hydrides with trialkyl alanes (317) has shown that the ease of formation increases with... 

Mixed complexes of PR3 with CO, alkenes, halides and hydride ligands in at least one oxidation state are common for all of the elements. 

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