Metals difluoride

The other important crystal structure for MX2 compounds is rutile (Ti02). Rutile [Section 5.4.1, 2 2P01/2(t), Figure 5.30] has an hep sequence of P layers filled by oxide ions, with Ti4+ ions in one-half of each O layer. Because all O sites are at C positions for an hep structure, partial filling of O layers avoids having Ti4+ ions in adjacent O sites. Compounds with the rutile structure are listed in Table 5.8. The structure is favored for transition metal difluorides and dioxides. 

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

The bond distance is taken from Brewer et al. (3 ). The bond distances for all of the transition metal difluorides from chromium through copper were estimated to be the same with the assessment that an error of 0.5 A would lead to an error of less than 1 cal K" mol" in the entropy. The bond angle and vibrational frequencies are those derived by Hastie et al. ( ) from infrared studies of matrix-isolated isotopic species. The electronic states and levels are assumed the same as those assigned to... 

The electronic levels are assumed to be the same as TiCl Cg). mts to the inverted states of NiClgCg) (2). The linear configuration is assumed because experimental evidence (3) indicates that other transition metal difluorides, viz those of Mn, Co, Ni, Cu, and Zn, are linear. 

A metal difluoride, MF2, adopts the tetragonal rutile structure, with lattice parameters a = 0.4621 nm, c = 0.3052 nm and density 3148 kg m-3. The molar mass of fluorine, F, is 18.998 gmoE1. Estimate the... 

CHA/KAR] Chattopadhyay, G., Karkhanavala, M. D., Chandrasekharaiah, M. S., Standard free energies of formation of metal fluorides by solid electrolytic galvanic cell method. I. Metal difluorides, J. Electrochem. Soc., 122, (1975), 325-327. Cited on page 120. 

Phases of the composition ARF4 are reported for A = Li, Na, Ag, K, Rb, and Cs. From a structural view-point, they can all be considered as metal difluorides with a disordered or partially/fully ordered cation sublattice. Disordered phases can be expected mainly if A and have similar radii and in fact, cubic fluorite-related (Na, R)F2 phases are observed at high temperatures as well as a few (K, R)F2 phases. In most cases, they are part of solid solutions (A, R)F2-j, which are structurally related to yttrofluorites as far as the anion-excess phases... 

While the 20 Group 1 metal halides all adopt either a face-centered or a body-centered crystal structure, crystals of the 32 dihalides of the Group 2 and 12 metals form a bewildering array of at least 15 different structure types. Both the crystal and the gas-phase structures have recently been described and correlated in comprehensive reviews by Hoffman and coworkers [16, 17]. In this section we shall be particularly concerned with the crystal stractures of the eight metal difluorides and the four mercury dihalides. 

No information is available about the conductivities of the Group 2 and 12 metal difluorides, presumably because of their high melting points and corrosive properties. The conductivities of the dichlorides are listed in Table 1. Like the conductivities of the alkali metal chlorides, the conductivities of the Mg, Ca, Sr, Ba, and Cd dichlorides lie in the range from 1.0 to 10 S cm . These compounds are good conductors and the melts presumably contain high concentrations of ions. 

Also, in anhydrous conditions, silver reacts with fluorine and forms silver difluoride AgFj and cobalt gives cobalt(III) fluoride, C0F3, these metals showing higher oxidation states than is usual in their simple salts. 

Significant vapor pressure of aluminum monofluoride [13595-82-9], AIF, has been observed when aluminum trifluoride [7784-18-1] is heated in the presence of reducing agents such as aluminum or magnesium metal, or is in contact with the cathode in the electrolysis of fused salt mixtures. AIF disproportionates into AIF. and aluminum at lower temperatures. The heat of formation at 25°C is —264 kJ/mol(—63.1 kcal/mol) and the free energy of formation is —290 kJ/mol(—69.3 kcal/mol) (1). Aluminum difluoride [13569-23-8] h.3.s been detected in the high temperature equihbrium between aluminum and its fluorides (2). 

Cobalt difluoride, used primarily for the manufacture of cobalt trifluoride, CoF, is available from Advance Research Chemicals, Inc., Aldrich Chemicals, and PCR in the United States, Fluorochem in the UK, and Schuhardt in Germany. The 1993 price varied from 60 to 200/kg depending on the quantity and the price of cobalt metal. C0F2 is shipped as a corrosive and toxic material in DOT-approved containers. 

Germanium difluoride can be prepared by reduction (2,4) of GeF by metallic germanium, by reaction (1) of stoichiometric amounts of Ge and HF in a sealed vessel at 225°C, by Ge powder and HgF2 (5), and by GeS and PbF2 (6). Gep2 has been used in plasma chemical vapor deposition of amorphous film (see Plasma TECHNOLOGY Thin films) (7). 

K [14881-07-3], Rb [72151 -96-3], and Cs [72138-72-8]), are prepared by reaction of elemental fluorine, chlorine trifluoride, or xenon difluoride and a mixture of nickel fluoride and alkaH metal fluorides or other metal haHdes (16,17). If the fluorination is carried out using mixed fluorides, a lower temperature can be used, yields are quantitative, and the final products are of high purity. Bis(tetrafluoroammonium) hexafluoronickelate [6310540-8], (NE 2N iF6> prepared from Cs2NiF3 and NE SbE by a metathesis in anhydrous HE, is also known (18). 

Handling and Safety Factors. Oxygen difluoride can be handled easily and safely in glass and in common metals such as stainless steel, copper, aluminum. Monel, and nickel, from cryogenic temperatures to 200°C (4). At higher temperatures only nickel and Monel are recommended. The compatibihty of OF2 with process equipment depends largely on the cleanliness of the equipment contaminants such as dkt, moisture, oil, grease, scale... 

AgF2 is prepared by the action of elemental fluorine on AgF or AgCl at 200°C. Both processes result in quantitative yields. Silver difluoride should be stored in Teflon, passivated metal containers, or in sealed quartz tubes. 

Xeaoa difluoride behaves as a fluoride ioa doaor toward many metal pentafluorides to form complex salts containing the XeF" and Xe2F" 2 cations (10). In reactions with the pentafluorides of arsenic, antimony, and mthenium, for example, it forms the salts Xe2F" 2AsF(, [21308-45-2], XeF" AsF(, [26024-71-5], [12528-47-1], XeF+Sbp-g [36539-18-1], [17679-45-7], [15364-10-0], [36539-19-2], [26297-25-6],... 

Chemical Reactivity - Reactivity with Water Reacts with water to form hydrogen fluoride, oxygen and oxygen difluoride Reactivity with Common Materials Reacts violently with all combustible materials, except the metal cylinders in which it is shipped Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The reagent NSF3 may also react via oxidative addition of an S-F bond to a metal centre to give a complex of the thiazyl difluoride anion [NSF2] , which is readily hydrolyzed to an NSO complex (Scheme 7.3). ... 

Of the anhydrous dihalides of iron the iodide is easily prepared from the elements but the others are best obtained by passing HX over heated iron. The white (or pale-green) difluoride has the rutile structure the pale-yellow dichloride the CdCl2 structure (based on cep anions, p. 1212) and the yellow-green dibromide and grey diiodide the Cdl2 structure (based on hep anions, p. 1212), in all of which the metal occupies octahedral sites. All these iron dihalides dissolve in water and form crystalline hydrates which may alternatively be obtained by dissolving metallic iron in the aqueous acid. 

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