Iron complexes fluorides

The validity of this approach can be demonstrated by the example of several complex fluoride compounds that exhibit ferroelectric properties, such as compounds that belong to the SrAlF5 family [402, 403]. The crystal structure of the compounds is made up of chains of fluoroaluminate octahedrons that are separated by another type of chains - ramified chains. Other examples are the compounds Sr3Fe2Fi2 and PbsWjOgFio. In this case, the chains of iron- or tungsten-containing octahedrons are separated from one another by isolated complexes with an octahedral configuration [423,424]. 

The values of AH for the thallium (III) halide systems becomes less exothermic as complex formation proceeds. There are no steps with about the same value of AH , in marked contrast to e.g. Hg2+ and Pd2+. The trend of AH is in fact opposite to that found for several t)q)ical hard-hard interactions, e.g. iron (III) fluoride, lanthanum sulphate and yttrium acetate (Table 1). An even more striking feature of the thallium (III) halides is that AS°n is approximately constant for all steps. This is indeed different not only from ions such as In +, Cd2+ and Zn +, where reversals of the decreasing trend of AS°n occur for certain steps, but also from Hg2+ and Pd + where the higher steps have a much lower value of ASn than the earlier ones. 

The previously reported susceptibility of the iron complex 35 toward fluoride ion to give the anionic compound 30 (see Section III,D) suggested that nucleophiles might react similarly with 64 to give anionic derivatives. Indeed, reaction of 64 with the soft nucleophile PMe3 yields the 1 1 adduct 68 (145). 

The potassium promoter is usually added as the carbonate but it was shown that the hydroxide, nitrate, fluoride, and the like, gave simQar results [15]. Highly-dispersed catalysts are formed when potassium/iron complex salts such as K Fe(C0)4 are supported on AljOj orSiOj [58]. After reduction,... 

Iridium(V) complexes, 1158 fluorides, 1158 Iridium(VI) complexes, 1158 Iron complexes acetonitrile, 1210 analysis, 1180, biological systems, 1180 coordination geometries, 1183 coordination numbers, 1182-1187 dinitrosyldicarbonyl, 1188 Mdssbauer spectroscopy, 1181 nitric oxide, 1187-1195 nitrosyls binary, 1188 bis(dithiolene), 1193 carbonyl, 1188 dithiocarbamates, 1192 halides, 1193 iodide, 1193... 

Methylbromoarsines, synthesis 26 Vanadium(III) fluoride, synthesis 27 Sulfur(IV) fluoride, synthesis 33 Peroxydisulfuryl difluoride, synthesis 34 Trichloro(tripyridine)chromium(III), synthesis 36 Tris(3-bromoacetylacetonato)chromium(III), synthesis 37 Trichloro(tripyridine)molybdenum(III), synthesis 39 Uranyl chloride 1-hydrate, synthesis 41 Rhenium(III) iodide, synthesis 50 Potassium hexachlororhenate(IV) and potassium hexa-bromorhenate(IV), synthesis 51 Iron-labeled cyclopentadienyl iron complexes, synthesis 54 Inner complexes of cobalt(III) with diethylenetriamine, synthesis 56... 

The value of the pH for optimum stability of silicic acid depends on what impurities are present in the solution. Traces of aluminum ions and to a lesser extent, iron, thorium, and beryllium ions tend to offset the effect of fluoride ion by forming complex fluorides and thus retard polymerization in this pH range. Depending on the purity of the solution, the pH of optimum stability may range from 1 to as high as 3-3.5. In silicic acid. solutions free from aluminum impurity, as little as 1 ppm of fluorine has a marked effect on the rate of polymerization in acid solution. 

The familiar thiocyanate test (see page 271) is not applicable to the detection of small amounts of iron in fluorides, because the tervalent iron is present as the complex [FeF ]- anion. The Fe+ ion concentration delivered by this complex is insufiicient for the formation of the red ferri-thiocyanate color. 

The methyl group of 56a is abstracted after addition of Ph3CBAr 4 (Ar = 3,5-(CF3)2C6H3) to produce the salt 58 after abstraction of the benzyl group of 56e with BfCeFsls, the arene adduct 61 is formed. 56e forms also a stable, tetrahedral 14-electron compound with pyridine. This adduct formation with the Lewis base causes a noticeable elongation of the Fe-C bond length compared to that of parent compound 56e [210.7(2) vs. 204.14(18) pm]. Furthermore, alkyl complexes 56 serve as precursors for discrete iron(n) fluorides by reaction with trimethyltin fluoride. " ... 

Stability constants of their iron complexes as presented in Table 7.1 [30,45-47]. The stability constants with one anion are given, which refers to the reaction order one that has usually been found for the dissolution of passive layers under the influence of the aggressive anions. The reaction of Fe + with HP to form FeF " and F1+ yields the more realistic value of log Kj = 2.28 due to the small dissociation constant of FIF (pFC = -log = 2.98). Table 7.1 also contains the constants K- for Ni +- and Cr3+-halide complexes. Their falling values from fluoride to iodide and Fe + to Ni + support the decreasing tendency for enhanced dissolution of the passive layer and localized corrosion. These data can be referred to the situation at the oxide surface. The fluoro complexes are very stable and form in high concentrations at all surface sites. Therefore their much faster transfer to the electrolyte yields enhanced general dissolution, whereas the attack of the other halides is locally restricted and much less pronounced. Besides the thermod5mamically based values, i.e., the stability constants, the kinetics of complex formation and of the complex transfer to the electrolyte are another decisive factor for the attack of the passive layer. In this sense, the situation of Cr is very special and will be discussed separately. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

Rubidium metal alloys with the other alkaU metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double haUde salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and 2iac. These complexes are generally water iasoluble and not hygroscopic. The soluble mbidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide. 

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