Binary compounds described

Although the formula of this phase is more complex than the binary compounds described above, the procedure is exactly the same. It is only necessary to identify the likely defect equilibria that pertain to the experimental situation. 

The formation of different oxidation states is an important feature of transition metal chemistry, as seen in the binary compounds described in Chapter 3. The conversion from one metal oxidation state to another in solution involves the transfer of electrons and this process is, by convention, written as a reduction (equation 5.20) ... 

B. N. Menschutkin [Chem. Zentralbl. (1910), I, 167] and also J. Boeseken [Chem. Zentralbl. (1911), I, 466] suggested that in the Friedel-Crafts reaction the three reacting components combined to form a ternary compound which then reacted further. This view was adopted and elaborated by J. Schmidlin and R. Lang [Ber. 45, 899 (1912)]. They considered the evidence for the existence of binary compounds described above, and concluded that the only satis-... 

Temary and quaternary semiconductors are theoretically described by the virtual crystal approximation (VGA) [7], Within the VGA, ternary alloys with the composition AB are considered to contain two sublattices. One of them is occupied only by atoms A, the other is occupied by atoms B or G. The second sublattice consists of virtual atoms, represented by a weighted average of atoms B and G. Many physical properties of ternary alloys are then expressed as weighted linear combinations of the corresponding properties of the two binary compounds. For example, the lattice constant d dependence on composition is written as ... 

Eight variants of the DD reaction mechanism, described by Eqs. (21-25) have been simulated. The simplest approach is to neglect B2 desorption in Eq. (22) and the reaction between AB species (Eq. (25)). For this case, an IPT is observed at the critical point Tib, = 2/3. Thus this variant of the model has a zero-width reaction window and the trivial critical point is given by the stoichiometry of the reaction. For Tb2 < T1B2 the surface becomes poisoned by a binary compound of (A -I- AB) species and the lattice cannot be completely covered because of the dimer adsorption requirement of a... 

This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

The ionic model, the description of bonding in terms of ions, is particularly appropriate for describing binary compounds formed from a metallic element, especially an s-block metal, and a nonmetallic element. An ionic solid is an assembly of cations and anions stacked together in a regular array. In sodium chloride, sodium ions alternate with chloride ions, and large numbers of oppositely charged ions are lined up in all three dimensions (Fig. 2.1). Ionic solids are examples of crystalline... 

It should not be inferred that the crystal structures described so far apply to only binary compounds. Either the cation or anion may be a polyatomic species. For example, many ammonium compounds have crystal structures that are identical to those of the corresponding rubidium or potassium compounds because the radius NH4+ ion (148 pm) is similar to that of K+ (133 pm) or Rb+ (148 pm). Both NO j and CO, have ionic radii (189 and 185 pm, respectively) that are very close to that of Cl- (181 pm), so many nitrates and carbonates have structures identical to the corresponding chloride compounds. Keep in mind that the structures shown so far are general types that are not necessarily restricted to binary compounds or the compounds from which they are named. 

The symbols suggested by Jensen, based on Niggli s proposals, describe the local coordination by means of coordination number ratios. For instance, a formula AEm/n will indicate a binary compound where m is the coordination number (defined as the nearest-neighbour number (NNN)) of atoms E around A and n is the similarly defined coordination number of A around E. 

Selenides, tellurides andpolonides. Se, Te and Po react easily with most metals and non-metals to form binary compounds (selenides and tellurides are common mineral forms of these elements). Non-stoichiometry is frequently observed in the compounds with the transition elements many of these compounds may be described as metallic alloys. The compounds of the metals of the first two groups may be considered the salts of the acids H2Se, H2Te, etc. The alkali metal selenides... 

Synthesis in liquidAl Al as a reactive solvent Several intermetallic alu-minides have been prepared from liquid aluminium very often the separation of the compounds may be achieved through the dissolution of Al which dissolves readily in several non-oxidizing acids (for instance HC1). For a review on the reactions carried out in liquid aluminium and on several compounds prepared, see Kanatzidis et al. (2005) binary compounds are listed (Re-Al, Co-Al, Ir-Al) as well as ternary phases (lanthanide and actinide-transition metal aluminides). Examples of quaternary compounds (alumino-silicides, alumino-germanides of lanthanides and transition metals) have also been described. As an example, a few preparative details of specific compounds are reported in the following. 

It has already been noticed (see 3.9.4) that according to the mentioned concepts several ternary compounds may be considered as the result of a sort of structural interaction between binary compounds. As a consequence some regular trend could also be predicted for their occurrence in their phase diagrams and in the description (and perhaps modelling) of their thermodynamic properties. A few details about this type of structural relationships will be considered in the following and, in this introduction, examples of blocks of simple structural types and of their combination in more complex types will be described. 

Binary Compounds. The thermodynamics of the formation of HfCl2, of HfCl4, fused sodium and potassium chlorides have been described. The reduction of ZrXj (X = Cl, Br, or I) with metallic Zr or A1 in molten AICI3 has been studied at temperatures from 250 to 360 °C, depending on the halide. The electronic spectra of the initial reaction products were consistent with either a solvated Zr complex or an intervalence Zr "-Zr" species. Further reduction resulted in the precipitation of reduction products which were identified by analysis and i.r., electronic, and X-ray powder diffraction spectra. The stability of the trihalides with respect to disproportionation was observed to increase from chloride to iodide thus ZrC and ZrCl2,0.4AlCl3 were precipitated, whereas only Zrlj was formed. ... 

Selenides. Selenium forms compounds with most elements. Binary compounds of selenium with 58 metals and 8 nonmetals, and alloys with three other elements have been described (55). Most of the selenides can be prepared by a direct reaction. This reaction varies from very vigorous with alkali metals to sluggish and requiring high temperature with hydrogen. 

As the valency of the metal increases, the bonding in these simple binary compounds becomes more covalent and the highly symmetrical structures characteristic of the simple ionic compounds occur far less frequently, with molecular and layer structures being common. Many thousands of inorganic crystal structures exist, ffere we describe just a few of those that are commonly encountered and those that occur in later chapters. 

The organometallic chemistry of the first-row transition metals generally starts with the binary metal carbonyl organometallic complexes. Noncarbonyl organometallic complexes starting with other easily accessible binary compounds provide entries to a broader spectrum of complexes. In this context, we describe the synthesis of the mixed sandwich complex (tj5-pentamethylcyclopentadienyl) ( j5-cyclopentadienyl) iron as an example of the synthetic utility of the solution-stable derivative (>j5-pentamethyl-cyclopentadienyl) (2,4-pentanedionate) iron. 

Solid-Solution Models. Compared with the liquid phase, very few direct experimental determinations of the thermochemical properties of compound-semiconductor solid solutions have been reported. Rather, procedures for calculating phase diagrams have relied on two methods for estimating solid-solution model parameters. The first method uses semiem-pirical relationships to describe the enthalpy of mixing on the basis of the known physical properties of the binary compounds (202,203). This approach does not provide an estimate for the excess entropy of mixing and thus... 

Commonly, many compounds with the same formula type have the same type of structure. Usually the most common compound is chosen as representative, but it could be the first structure of the type studied. For example, hundreds of binary compounds of the MX type have the same crystal structure as NaCl. Other compounds can be described as having the NaCl (or halite, the name of the mineral) structure. If the structure being considered has slight differences, these differences can be described in terms of the reference structure. One often sees statements such as a compound has a disordered spinel (MgAl204) type structure or an inverse spinel structure. This requires knowledge of the spinel structure because "inverse" or "disordered" terms describe variations of occupancies of octahedral and tetrahedral sites. 

A major portion of the effort on semiconductors has been expended on the binary compounds having the zinc blende or wurtzite structure. These are commonly classified by the A group numbers such as III-V (InAs) and II-VI (CdTe) and have what may loosely be described as a 1 to 1 cation-anion ratio. However, another series of compounds that has become of increased interest can be generally classified as the IV-VI compounds. Specifically, these are the chal-cogenides of germanium, tin, and lead. In this discussion, we present some experimental observations on the tellurides of these group IV A elements. 

Very few binary compounds of this class have been described, but CIO is widely used as a counter ion for the preparation of many of the cationic species of the other neutral ligands, despite the instability that gives some risk of explosion For many years, it was regarded as the standard for non-coordination —especially in aqueous solution—and both the chlorate and perchlorate crystallized from aqueous solution as [Mn(H20)6]X2. However, the anhydrous Mn(C104)2 can be... 

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