Metal halogen bonds

The complexing of zirconium and hafnium ions by fluoride ions is quite extensive compared to chloro complexing, while complex ion formation w ith bromide and iodide ions is negligible. Formation constants for fluoride complexing with zirconium(IV) and hafnium(IV) calculated from the data of Connick (126), Buslaev (94), and Hume (574), have been summarized graphically by Goldstein (213). Slightly different values have been published by Bukhsh (92). Noren (15a, 401-403) has redetermined the equilibrium constants for the reaction. 

In agreement with other workers, the constants for the first two species are larger for zirconium than for hafnium. Noren s data yields values for Ks Kq which are smaller than the values reported by earlier workers, and which are essentially the same for both zirconium and hafnium. The heptafluoro ion is known to be unstable with respect to dissociation in aqueous solution (307). 

Equilibrium data for the formation of the chloro complexes MCI MCI3+, and MCI4 have been determined using ion exchange tec niques at hydrogen ion concentrations of 2 and 4 M and at metal i( concentrations of 5 x 10 or less 353, 465). The values for the cumul tive formation constants are given in Table XXII. The strong absorptic 

Formation Constants or Chloro Complexes with Zirconium and Hafnium 

Additional properties of chloride solutions have been studied, namel the characteristics of constant boiling hydrochloric acid solutions zirconyl chloride 206) and activity coefficients of zirconium oxychlorii solutions 319). The ultraviolet spectra of hydrochloric acid solutions zirconium and hafnium have been recorded by a variety of investigatoi but no assignments of the spectra have been made to specific species solution 312, 353, 465, 537). 

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CFaSn bond is stable to reaction conditions that cleave the metal-halogen bond. 

Table 12a. Standard enthalpy of formation, A/ff(g), enthalpy of disruption, AHjy, and metal-halogen bond enthalpy contribution, (M-X), in metal carbonyl halides (kJ mol-1)...

A good fuel will react with oxygen (or a halogen like fluorine or chlorine) to form a stable compound, and substantial heat will be evolved. The considerable strength of the metal-oxygen and metal-halogen bonds in the reaction products accounts for the excellent fuel properties of many of the metallic elements. 

Metal-halogen bonds are more labile than meial-mirogen bonds. Use this informal ion and ihe Lrans effect to devise syntheses for the following geometric isomers from [PtCUl2-... 

Trimethylsilylated, mono- and disubstituted hydrazines react with complexes containing a metal-halogen bond (84, 85, 121). 

Some applications of the use of substituted disilyl mercury compounds, Hg(SiXa)2 (X = Me,Cl), are shown in Table III there is an early review article (421). In most cases, the mercury compound reacts with a metal-halogen bond to give a silicon halide and mercury as byproduct, e.g. (entry 1),... 

The reaction of metal-14 anions with the metal-halogen bond gave heterocyclization,... 

Insertion of plumbylenes into a metal halogen bond. 1309... 

The reducing power of the Sn—H bond can interfere with oxidative additions when metal-halogen bonds are present. For example, the reaction of cis- or trans-CpRe(CO)2Br2 with HSnPh3 yielded the dihydride CpRe(CO)2H2 and BrSnPh3. 

We have shown, however, that a significant number of monohalogen-oalkyl transition metal compounds have now been prepared, many of them in the last decade. A variety of routes have been used to synthesize these compounds, but the most common ones are (1) the reaction of an alkoxyalkyl compound with anhydrous HX (X = Cl, Br, or I), (2) the reaction of a nucleophilic transition metal compound with a dihaloalkane, and (3) the insertion of a methylene group into a metal-halogen bond. The most common route to the co-halogenoalkyl complexes is by reaction of an anionic metal species with the a,co-dihaloalkane. These monohalo-... 

Fig. 3. Dependence of the metal-halogen bond ionic character on the difference in the metal and halogen electronegativities (values of the electronegativities were obtained from references (65), (66) and (67))...

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