Oxyhalides and complexes

Chromium(vi) Complexes.—These studies have been virtually confined to oxyhalide and oxide systems. 

Boric acid forms complexes with a number of inorganic ions and organic molecules. Ammonia, hydrazine, hydroxides and oxyhalides from complexes with boric acid. The organics include diols, thiols, dioxane, pyridine and many other solvents in which boric acid dissolves. 

Compounds of the formulas Re(CH3)6, ReO(CH3)4, Li e CH ] [60975-25-9], Re02(CH3)3 [56090-011-8], and Re03CH3 [70197-13-6] have been prepared. The first two compounds were obtained from reaction of rhenium halides or oxyhalides and methyllithium the last three were formed from the species by oxidation or reduction reactions. The use of these hydride and alkyl complexes as catalysts is under investigation. 

Monomeric complexes of W1 1 such as the halides, the oxyhalides and their derivatives have been known for quite some time. In most cases these are six-coordinate, but higher coordination numbers are also known. During the last two decades, new structural types have been reported. Of these, the most interesting are the dinuclear complexes containing W=W double bonds and the trinuclear dusters containing W—W single bonds. 

Hala, J. Halides, Oxyhalides and Salts of Halogen Complexes of Titanium, Zirconium, Hafnium, Vanadium, Niobium and Tantalum, Vol, 40, Elsevier Science, New York, NY, 1989. 

Thorium forms one series of halides, another one of oxyhalides, and also a series of double or complex halides. In general, stability of these compounds toward heat decreases as die atomic weight of die halogen increases. These compounds are often isostructural with the corresponding compounds of other actinide elements in the (IV) oxidation state. 

Numerous 1 1, 1 2, and 1 3 neutral adducts are known for NbOCb. While complexes with N-donors such as amines, nitriles, or with phosphines derive mostly from direct reaction between oxyhalides and the ligands, many MOX3L2 complexes have been obtained by oxygen abstraction from O-donors by pentahalides. This reactivity can be exploited for an easy entry into oxychloride chemistry via the Labile NbOCl3(MeCN)2 complex (1) (equation 3). ... 

Finite ions and neutral molecules containing 0 directly bonded to a metal atom are formed by many transition metals. They include molecular oxyhalides and oxyhalide ions, which are included in Chapter 10, vanadyl and uranyl compounds, and numerous oxo-molecules and ions of metals such as Mo, Re, Os, etc. We give here a few examples of complexes of which the structures have been determined. The octahedral ion in K2 [0s 02(0H)4] has the same (trans) configuration as the anion in K2(0s02Cl4). Rhenium forms many octahedral ions (Re X40L) where X is halogen and L is H2O, CH3CN, etc. 

In this section we shall summarize what is known of the structures of the trioxides, complex oxides, and oxyhalides of these elements. In the trioxides and in the one complex oxide of Sb which has been studied the stereochemistry of the Group VB atoms is simple they form three pyramidal bonds like in P4O6. The behaviour of Sb in its oxyhalides and SbaO OH is less simple, and moreover different from that of Bi. For this reason the oxyhalides of Sb and Bi are considered separately. Structurally related to the oxyhalides of bismuth are a number of complex oxides which will also be mentioned. 

In the two more complex oxyhalides the characteristic structural feature is apparently a double chain, in which all the Sb atoms are 4-coordinated, which is joined through OH groups to form infinite layers [Sb808(0H)4] in the first compound and complex cylindrical chain ions [Sb40s(0H)] in the second. 

Molybdenumfvi) and Tungsten(vi).—Halide, Oxyhalide, and Related Complexes. The MF6-XeF2 (M = Mo or AV) binary systems have been studied by... 

A number of unique difficulties pertain to oxidation states of metal ions encountered in molten salt solutions. For example, for first-row transition metals, the highest oxidation state prevailing is often +3, as in the case of Fe and Cr. Frequently, for chlorides in particular, the +3 state compounds are volatile at suitable operating temperatures and, hence, their solutions are thermally unstable.Other problems encountered include rapidly dispropor-tionating states, the formation of oxyhalides, and precipitation of complexes by reaction with the melt. While redox reactions per se involve very fast charge transfer steps, these may occur at the extremes of the range of electrochemical stability, thus leading to concomitant solvent melt decomposition. Nevertheless, suitable processes such as Fe /Fe on vitreous carbon in chloride melts can be employed to determine the effective electrochemical areas of electrodes where diffusion coefficients are accurately known. ... 

IV - 10 Oxyhalides and hydroxyhalides IV - 11 Halide complexes alumino-fluorides IV - 12 Compound halides... 

Hala J (1989) Halides, oxyhalides and salts of halogen complexes of titanium, zirconium, hafnium, vanadium, niobium and tantalum. lUPAC, Blackwell, London... 

The only significant difference between halide melts and oxyhalide melts is that oxyfluoride complexes have a tendency to dissociate at relatively high concentrations yielding polyanion groups. This phenomenon is related with the need to achieve coordination saturation. 

No complexes have at present been authenticated in oxidation states greater than +6, whereas oxyhalide complexes exist where the +8 state is known this parallels trends in the halides and oxyhalides. 

Halide and oxyhalide complexes of elements of the titanium, vanadium and chromium sub-groups. 

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