Fluoride binary

In this review we summarize and attempt to correlate vibrational spectral data amassed from the literature for the main group, inorganic binary fluorides. In addition, a brief review of the matrix-isolation studies of both reactive intermediates and high-temperature fluoride vapor species is included, placing particular emphasis on the interhalogen molecules. 

In this section available vibrational data for the main group binary fluorides will be reviewed in an attempt to establish trends in both structures and bond-stretching force constants. The review is restricted primarily to molecular entities that were observed either in the gas phase or in inert matrices. The emphasis on the matrix data in this review is in contrast with the more general approach taken by Reynolds in an earlier review of the vibrational spectra of inorganic fluorides (2). 

Stretching Force Constants and Symmetry for Main Group Binary Fluorides  

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Both the binary and complex fluorides of aluminum have played a significant role in the aluminum industry. Aluminum trifluoride [7784-18-17, A1F., and its trihydrate [15098-87-0] 3 3H2O, have thus far remained to be the only binary fluorides of industrial interest. The nonahydrate [15098-89-2] 3 9H2O, and the monohydrate [12252-28-7, 15621 -55-3], AIF 20, are of only academic curiosity. The monofluoride [13595-82-9], AIF, and the difluoride [13569-23-8], AIF2, have been observed as transient species at high temperatures. 

Oxygen forms several binary fluorides of which the most stable is OF2. This was first made in 1929 by the electrolysis of slightly moist molten KF/HF but is now generally made by reacting F2 gas with 2% aqueous NaOH solution ... 

It is from the binary fluorides that other compounds of xenon are invariably prepared, by reactions which fall mostly into four classes ... 

Predominant formation of either complex fluoride or complex oxyfluoride depends on the interaction rates ratio of processes (25) and (26). The relatively high interaction rates of (27) and (28) lead to the synthesis of simple fluorides or oxyfluorides, respectively. With the availability of two or more cations in the system, the ammonium complex fluorometalates interact forming stable binary fluorides or oxyfluorides or mixtures thereof. 

As osmium forms a tetroxide, OsFg might possibly exist, especially in view of the existence of the osmium(VIII) oxyfluorides, but MO calculations indicate the Os—F bond would be weaker in the binary fluoride. It is also likely that non-bonding repulsions between eight fluorines would make an octafluoride unstable [23b],... 

Vibrational Spectra of the Binary Fluorides of the Main Group Elements... 

First, let s look at some trends. The binary fluorides of the second period exhibit a consistent increase in shielding, as reflected by the significant decrease in their 19F chemical shifts (more negative) as the difference in electronegativity of the bound atom and fluorine... 

Electronegativity arguments obviously cannot explain the lack of trend in chemical shift for the third-period binary fluorides. The unexpectedly large shielding exhibited for SF2 and C1F has been attributed toai -> a excitation caused by the external magnetic field.1... 

To investigate this further the enthalpies of formation Ajy uH of all the ternary fluorides from the binary fluorides,... 

Binary fluorides, methods of preparing noble-gas, 77 335-336 Binary heterogeneous polymer blends compliance of, 20 347-348 moduli of, 20 346-347 nonlinear viscoelastic behavior of, 20 348 yield and/or tensile strength of, 20 348-349... 

Some of the few complete sets of enthalpies for binary fluorides are collected in Tables XVIII and XIX. The inversion in dissociation heats for copper and beryllium fluorides can be associated with the closed-shell configurations of Be2+ and Cu+. The alternations in bond energies... 

The question as to the best formulation of structures and species in some binary fluoride systems was the subject of extensive experimental investigations, involving infrared and Raman spectroscopy in the molten state and in solutions as well as NMR spectroscopy and conductometric and cryoscopic measurements. Some crystal structure studies have also been published. The systems of SeF4 with BF3, SbF5, AsF5, NbF5, and TaFs have been studied recently. 

Fro. 7. i F Shielding parameters for the binary fluorides plotted against the atomic number of the central atom—molecular species. ( )ai((calc.) (DjaiS) o)ap 8) ( ) CTp(obs.). 

Xenon forms three binary fluorides, XeF2, XeF4, and XeFe. Fluorine is the only element with which xenon reacts directly forming XeF2. Reactions occur with excess xenon under pressure ... 

For the following discussion of structure types the fluorides are divided into different groups according to the atomic ratio Me F. Within each group the binary fluorides are mentioned first, followed by the ternary compounds arranged in the order of the atomic ratio A Me. (Here Me stands for an ion of the transition series and A for an alkali- or alkaline earth ion or their isomorphous substitnent.)... 

Binary fluorides MeF2 shall not be discussed here in detail. With the exception of the fluorite structures of CdFa and HgFa they crystallize in the tetragonal rutile type. In this structure the MeFg-octahedra share opposite edges and form chains that are at the same time 3-dimensionally linked in corners. The Me—F—Me angles in the chains are 90° and between them about 130°. 

Similar chain structures are well known of other compounds and seem to be preferred by ternary scdts, the A-ions of which are between the chains and hold them together. Binary fluorides on the other hand seem to prefer the forming of closed, finite groups, i. e. low rather than high polymer molecules. In the a-modification of UFj, however, such a chain stmcture is also found (343). But by the arrangement of chains further ligands in a second sphere are added to those of the primary octahedral coordination of the uranium. 

In this context the binary fluoride NbFa.s should be referred to also. In the structure of this compound isolated polynuclear groups NbeFia are 3-dimensionally infinitely linked by additional fluorines (296). This is the only exeimple of a fluoride so far, in which discrete Men-clusters have been observed, indicative of metal-metal bonding 279, 295). 

The ions of the first members of the second and third transition series (Me + = Y, La and Me + = Zr, Hf) are so large, as to achieve higher C.N.s than 6 already in some compounds AMe +F4 (page 33) and AgMe +Fj (47, 42) as well as in their binary fluorides (pages 37, 30). To deal with these structures which correspond closely to those of the lanthanide and actinide fluorides, is beyond the scope of this review. As for the stereochemistry of 8-coordination the reader is referred to papers by Clark et al. 68) and Kepert 189). 

Among the noble gas fluorides, the binary fluorides of xenon have received the most attention as fluorinating agents. Krypton fluorides seem to be more exotic novelties than real reagents. 

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