Binary metal fluorides

Li H, Balaya P, Maier J. Li-storage via heterogeneous reaction in selected binary metal fluorides and oxides. J Electrochem Soc. 2004 151(ll) A1878-85. 

The most common methods of preparing anhydrous binary metal fluorides in the laboratory are based on reactions of gaseous HF or F2 with suitable solid substrates. With HF, the oxidation state of the starting material is preserved, whereas with F2, the fluoride with the highest stable oxidation state is obtained. The reactions are mostly carried out in tubes of Monel (a Cu/Ni alloy) at temperatures up to about 400-600 °C. As starting materials, hydrated fluorides (obtained from aqueous HF solutions), chlorides, carbonates, or easy decomposable ternary compounds like NH4Mnp3 may be used, as shown by the following examples (2-4) ... 

Rhenium combines with Fg under a little pressure to produce a pale yellow solid, ReF, which is the highest binary metal fluoride known. At... 

Only quasi-binary metal fluoride systems containing one alkali fluoride component have been investigated since about the year 1980 (see Table 19). Some of the investigations were carried out by the study of ion molecule equilibria (see Sect. 5.5). 

Difluorine combines directly with all elements except O2, N2 and the lighter noble gases reactions tend to be very violent. Combustion in compressed F2 (fluorine bomb calorimetry) is a suitable method for determining values of Af77° for many binary metal fluorides. However, many metals are passivated by the formation of a layer of nonvolatile metal fluoride. Silica is thermodynamically unstable with respect to reaction 16.5, but, unless the Si02 is powdered, the reaction is slow provided that HF is absent the latter sets up the chain reaction 16.6. 

The fluorolytic sol-gel synthesis of metal fluorides was originally developed and explored for aluminium fluoride, which was a piece of luck since both the stepwise synthesis and the properties of HS-AIF3 showed the influence of the new synthesis process. Thus, almost immediately after exploration of HS-AIF3 other binary metal fluorides have been similarly prepared and attempted syntheses of more complex systems started. 

Binary metal fluorides Many binary metal fluorides have been prepared via sol-gel fluorolysis [4, 7]. The applicability of the synthesis process is primarily limited by the ready availability of soluble metal alkoxides. However, the synthesis of metal fluorides, of which the metal ions are very weak Lewis acids, typically does not result in sol formation but finely dispersed solid fluorides, the XRD of which reflect the aimed-for compounds. 

The atomic and ionic properties of an element, particularly IE, ionic radius and electronegativity, underly its chemical behaviour and determine the types of compound it can form. The simplest type of compound an element can form is a binary compound, one in which it is combined with only one other element. The transition elements form binary compounds with a wide variety of non-metals, and the stoichiometries of these compounds will depend upon the thermodynamics of the compound-forming process. Binary oxides, fluorides and chlorides of the transition elements reveal the oxidation states available to them and, to some extent, reflect trends in IE values. However, the lEs of the transition elements are by no means the only contributors to the thermodynamics of compound formation. Other factors such as lattice enthalpy and the extent of covalency in bonding are important. In this chapter some examples of binary transition element compounds will be used to reveal the factors which determine the stoichiometry of compounds. 

Table 3.2 Simple binary transition metal fluorides ...

It was soon apparent that for the binary platinum metal fluorides the metal atom was always in an octahedral or pseudooctahedral environment. In the trifluorides each F ligand was shared between two metal atoms, whereas in the molecular hexafluoride each F ligand belonged uniquely to the metal. Each metal atom in the... 

Other fluorofullerenes are obtained by reaction with metal fluorides. These may be less reactive than elemental fluorine, but consequently enable a much better selectivity in product generation. Depending on the metal chosen (either transition or rare earth metals might be considered), the composition of the fluorine compound ranges from C )F2 to about C60F36. Not only binary, but also ternary metal fluorides can be employed (Table 2.10). 

The only binary halide of Mn(lV) is MnF4, prepared from the elements. It is an unstable blue solid which decomposes at ambient temperatures (equation 21.50). Crystalline MnF4 is dimorphic. The building blocks in ot-MnF4 are tetramers like those in VF4 and p-CrF4 (21.14). However, in these three metal fluorides, the assembly of the tetramers differs and in ot-MnF4, they are linked to give a three-dimensional network. 

For M(V) and M(VI), no binary compounds with the heavier halogens and no oxides are known. Iridium(VI) fluoride is the precursor to [Ir(CO)g] +, the only example to date of a tripositive, binary metal carbonyl cation. Compare reaction... 

The full reduction of the metal oxide enables one to prepare composite materials consisting of nanometer-sized metallic particles dispersed in a Li20 matrix. The nanodimensional size of the metal particles is instrumental in making the reactions highly reversible. Conversion reactions are not limited to metal oxides, as it is now clear that there are a number of other systems that can be used, including sulfides, nitrides, phosphides, and fluorides. For a binary metal compound (MX ), with X = F, O, S, N, these reactions proceed as follows ... 

G. A. Bukhalova, 1. V. Mardirosova, Izv. An. SSR Neorg. Mater. 1966,2,2015-2019. Complex formation in binary systems of alkali metal fluorides and metaphosphates. 

A few classes of materials, such as binary copper compounds (copper sulfide CuS and copper oxide CuO) and metal fluorides undergo a conversion reaction... 

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