Solid State Structures of the Binary

SOLID-STATE STRUCTURES OF THE BINARY FLUORIDES OF THE TRANSITION METALS... 

Solid-State Structures of the Binary Fluorides of the Transition Metals A. J. Edwards... 

A second-order structural transformation in La uC at 233 5°C was reported (118) in a thermal expansion study. The LajCu04 product was prepared at high temperature (1100°C) by the solid-state reaction of the corresponding binary oxides. The material was found to decompose above 1200°C with the loss of oxygen. Samples of La uC, prepared at 1200°C, then maintained at 750°C in vacuum, yielded products having the general composition La2Cu04.x, or... 

In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride (100) and of tellurium tetrachloride on twinned crystals (65, 66) were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties (e.g., 66,161,168,169,219,220, 412), as well as the synthetic potential of the compounds. In contrast to the monomeric molecular i//-tbp gas phase structures with C2v symmetry (417), the solid state structures of both are polynuclear. As the prototype of the chlorides and bromides of selenium and tellurium, crystalline tellurium(IV) chloride has a cubane-like tetrameric structure with approximate Td symmetry (Fig. 1). Within the distorted TeCla+a octa-hedra the bonds to the triply bridging chlorine ligands are much longer than to the terminal chlorines. The bonding system can be described either covalently as Te4Cli6 molecules, or, in an ionic approximation, as [(TeCl Cn4] with a certain degree of stereochemical activity of the lone pairs toward the center of the voluminous cubane center (65, 66). 

The only binary halide of Mn(III) is the red-purple MnF3 which is made by the action of F2 on Mn(II) halides at 520 K. It is thermally stable but is immediately hydrolysed by water. The solid state structure of Mnp3 is related to those of TiF3, VF3, CrF3, Fep3 and C0F3 but is Jahn-Teller distorted (high-spin fi " ) there are, however, three... 

Probably hundreds of individual binary, ternary, and more complex compounds have been synthesized in solution, in the solid state (through decomposition or sintering) and in melts the compounds have been characterized by spectroscopic and thermal techniques, and now are being studied increasingly by single-crystal X-ray diffraction methods. The first crystal structures of the binary and ternary compounds were determined in the 1960 s and 1970 s, respectively, but already well over 50 structural determinations have now been published. Attempts have been made to correlate the structmes with spectroscopic and other properties. 

Our knowledge concerning soluble metal complexes with sulfide ions as ligands has increased considerably during the last two decades and this kind of Compound is still of topical interest. Some of the reasons for this are the development of a very flexible and fascinating structural chemistry of multinuclear metal-sulfur complexes, the fact that the active sites of some electron transfer proteins contain metal ions and labile sulfur,41,42 and also the relation of metal-sulfur cluster compounds to some heterogeneous catalysts. In addition, apart from the numerous binary and ternary sulfides which occur in nature, we have at our disposal a rich solid state chemistry of metal sulfides, which has been reviewed elsewhere and will be excluded here.43"17... 

Recent developments in the synthesis, structures, and properties of ionic/covalent ternary nitrides are reviewed. A description, including synthetic conditions, is given of preparative methods reported in the literature. Solid state synthetic reactions from binary nitrides as well as novel synthetic approaches such as amide synthesis and ammonolysis of ternary oxides are described. Examples of common structure types as well as electronic and magnetic properties are discussed. 

The main body of stmctural material in the solid-state chemistry of fluorides has been elaborated in the 1960s to the 1980s and is collected and discussed in several reviews. A good collection of data is tabulated in Ref. 35. A recent survey from the point of view of materials science is given in Ref. 36. Here, a short survey will be given on the most important basic structural features and relations in binary and ternary (and higher) compounds, combined with an attempt to account for modem developments. 

Ternary phases with structures different from those of the phases of the binary boundary systems are more the exception than the rule. Such phases have been reported in the systems Nb-Mo-N, Ta-Mo-N, Nb-Ta-N, Zr-V-N, Nb-Cr-N, and Ta-Cr-N. Information about ternary transition metal-nitrogen systems is often available for specific temperatmes only. This is even more the case for quaternary nitride systems, which play a role in the production of carbonitride cermets where quaternary compounds of the types (Ti,Mo)(C,N) and (Ti,W)(C,N) are of interest (see Carbides Transition Metal Solid-state Chemistry), as well as in layer technology where titanium nitride-based coatings of the type Ti(C,B,N) are prepared by magnetron sputtering. Layers consisting of ternary compounds of the type (Ti,Al)N and (Ti,V)N also have favorable properties with respect to abrasion resistance. 

There has been a strong effort to rationalise and elucidate a structural principle which will account for all the anion-deficienl, fluorite-related, mixed-valent binary oxides of cerium, praseodymium and terbium. This is a key step not only for the solid-state chemistry of these materials but also for a large class of fluorite-related materials involved in applications such as fast oxygen conductors and as catalysts. The two main theoretical approaches to the problem were developed by Martin and by Kang and Eyring, and will be illustrated in the following sections. 

The temperature-composition phase diagram constructed from thermal arrests observed in the MoFe-UFa system is characteristic of a binary system forming solid solutions, a minimum-melting mixture (22 mole % UFe at 13.7°C.), and a solid-miscibility gap. The maximum solid solubility of MoFq in the UFe lattice is about 30 mole % MoFe, whereas the maximum solid solubility of UFe in the MoFe lattice is 12 to 18 mole % UFe- The temperature of the solid-state transformation of MoFe increases from ——lO C. in pure MoFe to 5°C. in mixtures with UFe, indicating that the solid solubility of UFe is greater in the low temperature form of MoFe than in the high temperature form of MoFe- This solid-solubility relationship is consistent with the crystal structures of the pure components The low temperature form of MoFe has an orthorhombic structure similar to that of UFe. 

IR-4.2.3 Structural formulae and the use of enclosing marks in formulae IR-4.2.4 Formulae of (formal) addition compounds IR-4.2.5 Solid state structural information IR-4.3 Indication of ionic charge IR-4.4 Sequence of citation of symbols in formulae IR-4.4.1 Introduction IR-4.4.2 Ordering principles IR-4.4.2.1 Electronegativity IR-4.4.2.2 Alphanumerical order IR-4.4.3 Formulae for specific classes of compounds IR-4.4.3.1 Binary species... 

Finally, X-ray diffraction has been used to examine the liquid structure of binary ionic liquids of 1,3-dialkylimidazolium fluoride with HF [173,174], The solid state and liquid structures are closely related as both contain [HF2] anions. In contrast, Shodai et al. reported that the structure of liquid [(CH3)4N]F HF (n = 3-5) has a range of anion structures of the form [(HF)jcFp (x = 1-3). In this case, structures with x = 4 or 5 were not found in the liquid phase although similar compositions have been found in the solid state [175], These studies show that even elements that are rarely studied in the IL context like P (other than in PF ( or phosphonium cations) or F could provide access to interesting and potentially useful ILs. 

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