Oxo-salts

The cation-to-anion vibrations (lattice vibrations) are mainly located in the FIR region and their assignments, based on similar considerations to those reported for ionic oxides, are frequently difficult. 

Thus 28 IR active modes are expected to fall in the regions of the vibrations of the orthosilicate anions. Of these, we can expect five modes associated with V3 (asymmetric stretching) and two modes associated with Vi (symmetric stretching), three modes associated with the symmetric deformation (V2) and five with the asymmetric deformation V4, four hindered rotations, four hindered translations, and, finally, five modes associated with Al—O tetrahedra. We actually observe at least 10 components for framework vibrations. Additionally, the low-frequency modes of Na ions are expected to fall in the FIR region [68], where several bands are indeed observed. 

The structure of NaX zeolite also belongs to the Fm3c = 0 = 226 space group, with Z = 8. Thus, also in this case we expect 28 IR active fundamentals, while we observe at least nine components for the framework spectrum. 

In the case of vanadyl pyrophosphate, a very relevant oxidation catalyst, the IR spectra also provide information on the morphology, allowing the distinction of very active catalysts from less active, highly crystaUine, materials [71]. 

Highly sihceous zeoHtes (with Si/Al ratios 1) are microporous framework alumino-sihcate materials. Discussion of the framework skeletal vibrahons of highly sihceous zeolites is similar to that reported above for silicas. The addition of aluminum in the framework causes shifts in the positions of the sole band. In particular, the asymmetric Si—O—Si stretching modes of framework silicates, usually observed as a complex very strong absorption in the region 1200-1000 cm , tend to shift down a litde with A1 for Si subshtution. 

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The oxoacids of P are more numerous than those of any other element, and the number of oxoanions and oxo-salts is probably exceeded only by those of Si. Many are of great importance technologically and their derivatives are vitally involved in many biological processes (p. 528). Fortunately, the structural principles covering this extensive array of compounds are very simple and can be stated as follows ... 

Holmium oxide is prepared by thermal decomposition of carbonate, oxalate, hydroxide, nitrate, sulfate, or any oxo salt of holmium ... 

Lanthanum oxide can be produced by direct combustion of lanthanum in oxygen or air. The oxide also may be prepared by decomposition of an oxo salt of lanthanum, such as nitrate, sulfate, carbonate, hydroxide or oxalate. 

Among Tb oxo salts are the monoclinic nitrate hexahydrate Tb(N03)3 6H20, the tetragonal oxychloride, TbOCl, and the rhombohedral oxyfluoride, TbOF. 

The Reactions section highlights only important reactions that include formation of binary compounds, oxo salts, and complexes. 

Oxo salts of nitrogenous bases chlorates (VII), dichromates (VI), nitrates (V), iodates (V), chlorates (III), chlorates (V), and manganates (VII) of ammonia, amines, hydroxylamine, guanidine, etc. 

Black crystalline CuO is obtained by pyrolysis of the nitrate or other oxo salts above 800°C it decomposes to Cu20. The hydroxide is obtained as a blue bulky precipitate on addition of alkali hydroxide to cupric solutions warming an aqueous slurry dehydrates this to the oxide. The hydroxide is readily soluble in strong acids and also in concentrated alkali hydroxides, to give deep blue anions, for example, [Cu(OH)4]2" and [Cu(OH)6]4". In aqueous ammonia deep blue ammine complexes are formed, as described later. 

Simple hydrated oxo salts are known, as well as some double salts such as K2S04-Sc2(S04)3-nH20, which is very insoluble in K2S04 solution. Ammonium double salts such as the tartrate, phosphate, and oxalate are also insoluble in water. 

In the case of crystaUine sohds, more than one equivalent structural unit may be present in the primitive cell. This results in sphttings of the fundamental vibrational modes of these units. In the case of many crystalline solid materials covalent units (e.g. oxo-anions for oxo-salts) are present, together with other groups bonded by ionic bonds (e.g. the cations in the oxo-salts). According to the above group approximation, the internal vibrations of the covalent units can be considered separately from their external vibrations hindered rotations and translations of the group that finally contribute to the lattice vibrations and to the acoustic modes of the unit cell) and those of the other units. The presence of a number of covalent structural units in the primitive cell, causes their internal modes to spHt... 

There are no nitrates or carbonates of these metals, the only oxo-salts of importance being the sulphates of vanadium. A solid sulphate has not been obtained from a solution of VgOg, that is vanadium with charge number + 5, in H2SO4, but reduction of the solution gives sulphates of vanadium with charge numbers +4, +3 and +2 respectively ... 

With six electrons in the valence shell the simplest ways in which the octet can be completed are (a) the formation of the ion 0 ", (b) the acquisition of one electron and the formation of one covalent bond, as in the ion OH", and (c) the formation of two electron-pair bonds. The ions 0 and 0H are found in the oxides and hydroxides of metals. Although the 0 atom could, in principle, form a maximum of four covalent bonds, since there are four orbitals available, the formation of more than two essentially covalent bonds is rarely observed (see below). Assuming that the bond arrangement is determined by the number of a bonds and lone pairs we may summarize the stereochemistry of oxygen as shown in Table 11.1. We have included one case where 0 forms two collinear bonds, the ion Ru20Cljo ( 403), in which the bonds from the 0 atoms have considerable double-bond character other examples will be found in the section on Oxo-salts . The collinear bonds in Sc2Si2 07 are mentioned later. 

Direct combination of elements (A+B->AB) may often be used to prepare binary compounds. Combination with polyatomic reactants such as organic compounds is also possible. Decomposition reactions include the formation of oxides by heating the oxo-salts or hydroxides of metals. 

The Ln3+ state is the most stable under normal conditions for all elements in the series. Halides LnX3 and oxides Ln203 are known for all elements, as well as an extensive range of oxo salts... 

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