Vanadium complexes fluoride

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 cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

In general, Group 5 fluorides tend to adopt a preference for higher oxidation states, and as a consequence, over the past few years, there have been virtually no reported examples of low valent fluoro complexes of vanadium, niobium or tantalum. 

Tungsten, molybdenum, and vanadium interfere in the determination of niobium. In contrast to the corresponding tungsten complex, the niobium-thiocyanate complex is decomposed by oxalic acid. Fe(ni), U, Ti, and Ta do not interfere if they are present in no greater than hundred-fold amounts relative to niobium. Phosphate and fluoride interfere, but the latter can be masked with aluminium ions [37]. 

The chief interference is from Fe(lll), which forms a green complex with chromotropic acid. Before the determination of Ti, larger quantities of iron should be separated or smaller ones reduced with ascorbic acid or sulphite. Vanadium in quantities not exceeding those of titanium has no appreciable effect on the determination of Ti. Molybdenum at concentrations below 50 pg/ml does not interfere. Fluoride interferes by masking titanium, but can be removed by fuming with H2SO4. Oxidants (e.g. HNO3) must be absent because chromotropic acid is fairly easily oxidized. 

Vanadium (V, at. mass 50.94) occurs in the V, IV, III, and II oxidation states, vanadium(V) compounds being the most stable. In alkaline medium, the colourless vanadate VOs ions exist, whereas in strongly aeidic media, the yellow V02 cations are present. Within the intermediate pH range polymerized orange-yellow anionic forms occur. Vanadium(V) forms heteropoly acids with P(V), Mo(VI), and W(VI), and also peroxide complexes. Vanadium(IV) occurs as the blue vanadyl ion V02", stable in acid solutions and readily oxidized to vanadium(V) in alkaline solution. The VO cation is amphoteric. At pH 4, V0(0H)2 precipitates and at pH 9 it dissolves. Vanadium(IV) forms fluoride-, oxalate-, and... 

The IV state. This is the most important oxidation state of Ti where the main chemistry is that of Ti02 and TiCl4 and its derivatives. This is also an important state for vanadium which forms the vanadyl ion V02+ and many derivatives, cationic, anionic, and neutral containing the VO group. For the remaining elements, Cr-Ni, the IV state is found mainly in fluorides, fluoro complex anions, and cation complexes however, an important class of compounds are the salts of the oxo ions and other oxo species. 

As usually prepared, uranium hexafluoride may he contaminated with other volatile fluorides, and hydrogen fluoride, molybdenum hexafluoride, vanadium oxyfluoride are among the common and objectionable impurities that may be present. Purification is usually achieved by distillation procedures and a considerable amount of useful and practical information on purification procedures has recently become available (24, 62, 81). A procedure for the purification of UFe that has been recently introduced by Gathers el al. (16) involves the formation of a complex compound between uranium hexafluoride and an alkali metal fluoride. Ruff and Heinzelmann (68) first observed complex formation between uranium hexafluoride and sodium or potassium fluoride, and this was confirmed by Martin et al. (69). These reports were received with a certain reserve, because efforts made during World War II to prepare addition compounds of uranium hexafluoride were singularly unsuccessful (41). Nevertheless, complex compounds are indeed formed, according to the reaction... 

With the metals of the first transition series, the maximum coordination number of higher oxidation states is six, and this is so firmly fixed that in their fluoride complexes the oxidation state of the metal in question can be fixed by controlling the mol fraction of alkali metal present 26). Thus, the fluorination of a vanadium salt in the presence of a one, two, or three mol ratio of potassium ion, yields KV F6, KgWVFe, or KsV Fe. The same tendency is shown, but to a lesser degree, by metals of the second transition series, as exemplified by KRuFe and KgRuFe. For an unusual example in the third series, note that OsFe is known, OsFt is not stable, but heptavalent osmium is found as six-coordinated OsOFs (27). 

The effectiveness of Ziegler-Natta catalysts of the triethylaluminum-titanium tetrachloride type seems to be the subject of some controversy. One patent describes the formation of poly(vinyl fluoride) with such a catalytic system in THF in a bottle polymerization at 30 C and autogenous pressure for 6 hr [57]. A complex of triisobutylaluminum, vanadium oxytrichloride, and THF is said to be particularly effective at 30°C both for the homo- and copolymerizations of vinyl fluoride [58, 59]. The processes are said to resemble typical Ziegler-Natta systems and are independent of the THF concentration when the mole ratio of THF to VOCI3 was greater than 2.3 1. The use of triisobutylaluminum with tetraisopropoxytitanium at 30°C for 15 min is said to lead to a process with an ionic-coordination mechanism [60]. 

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