Complex oxides and halides

Kubaschewski (1972) collected and compared the enthalpies of formation of complex oxides from binary oxides. He did not offer any systematic correlation of these enthalpies with structural properties. Hoppe (1966,1970a, b, 1975) developed the MAPLE concept (Madelung part of lattice energy) as a tool to guide the structural interpretation of bonding in complex oxides and halides. It requires as input parameters the unit cell of a compound and positions of all atoms, and it treats the crystal as an ionic array of point charges. If crystal structure determinations have been properly done, MAPLE calculations for a complex compound are within 2% (sometimes larger, sometimes smaller) of the MAPLE values of the binary (parent) compounds. Therefore, purely ionic-model calculations are not suflftciently sensitive to correlate quantitatively with the relatively small enthalpies of solid-state complexation. 

Sections 4.1.2 and 4.1.3 compared complex oxides and halides with the binary (parent) compounds. In this section we attempt to show on a semiquantitative basis how complex oxides and halides favor high oxidation states, primarily because they represent acid-base reactions in which the presence of a basic oxides (e.g., BaO) or halide (e.g., CsCl) donates electron pairs (Lewis basicity) to the acidic (high charge density) f-element ion. 

Trzcinskabancroft, B., Knachel, H., Dudis, D., Delord, T.J. and Marler, D.O. (1985) Experimental And Theoretical-Studies Of Dinudear Gold(I) And Gold(II) Phosphorus Ylide Complexes - Oxidative Addition, Halide Exchange, And Structural-Properties Including The Crystal And Molecular-Structures Of [Au (CH2)2PPh2]2 And [Au(CH2)2PPh2]2(CH3) Bri. Journal of the American Chemical Society, 107(24), 6908-6915. 

Chromium(IV) and chromium(V), previously encountered as the oxides and halides and as unstable intermediates in solution, are now represented by complexes of ligands stabilized by heavy substitution against oxidation by the metal ion, and oxo and nitrido derivatives. These remain unimportant oxidation states compared with molybdenum and tungsten. 

In addition to oxides and halides, high oxidation states are sometimes found with surprising ligands, such as in the ion [ReH9]2- (1), which is formally a hydride complex of Re(VII). 

Finally, a mention should be made about the one peroxo system which will become more and more dominant the organometallic oxides of rhenium(VII). Such compounds have been found to be of outstanding catalytic activity for a number of oxygen transfer reactions with hydrogen peroxide.92 The best studied complex is methyltrioxorhenium(VII) (MTO) and its congeners. Figure 2.32 illustrates its synthesis. Epoxidation, aromatic oxidation and halide oxidation with these complexes have been studied with hydrogen peroxide and shown to be remarkably efficacious. 

Octahedral six-coordination is the most common chemical environment for the transition elements (see Coordination Numbers Geometries). Apart from the great number of octahedral complexes, the formally ionic oxides and halides usually adopt stmctmes in which the cation is in an octahedral... 

The simplest systems containing ionic bonds are the gaseous molecules of alkali halides and oxides, the structures of which are noted in Chapters 9 and 12 we refer later to the halide molecules in connection with polarization. The importance of the ionic bond lies in the fact that it is responsible for the existence at ordinary temperatures, as stable solids, of numerous metallic oxides and halides (both simple and complex), of some sulphides and nitrides, and also of the very numerous crystalline compounds containing complex ions, particularly oxy-ions, which may be finite (CO3 , NO3, SOl", etc.) or infinite in one, two, or three dimensions. 

Introduction.—A report has been published listing heats of reaction and formation for chromium oxides and halides and for some chromates. Inorganic pyro compounds, M (X207)j, have been reviewed with consideration of species with X = Cr. A review of X-ray diffraction studies of the molecular structure of a number of Cr, Mo, and W complexes and organometallic compounds has appeared. ... 

Ternary structures gomc ternary oxides and halides may have discrete complex ions such as > others have structures with no such discrete ions. Silicates show a range of intermediate possibilities. The compound formula alone does not indicate the structure type. 

Al111 is octahedral in fluorides and in most oxides (including many complex oxides), and tetrahedral with larger or less electronegative atoms (and sometimes also in oxides). Heavier halides form molecular dimers A12X6. The tetrahedral [A1H4] complex and dimeric alkyls are... 

An authoritative review on the chemistry of radon, which includes the formation of clathrate compounds, the simple and complex fluorides, ionic radon in solution, redox properties, and the various unsuccessful efforts to prepare an oxide and halides of radon other than the fluoride, was published by the most significant contributor to this field in 1983 (14). 

Several Pd(0) complexes are effective catalysts of a variety of reactions, and these catalytic reactions are particularly useful because they are catalytic without adding other oxidants and proceed with catalytic amounts of expensive Pd compounds. These reactions are treated in this chapter. Among many substrates used for the catalytic reactions, organic halides and allylic esters are two of the most widely used, and they undergo facile oxidative additions to Pd(0) to form complexes which have o-Pd—C bonds. These intermediate complexes undergo several different transformations. Regeneration of Pd(0) species in the final step makes the reaction catalytic. These reactions of organic halides except allylic halides are treated in Section 1 and the reactions of various allylic compounds are surveyed in Section 2. Catalytic reactions of dienes, alkynes. and alkenes are treated in other sections. These reactions offer unique methods for carbon-carbon bond formation, which are impossible by other means. 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

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