Alkaline Earth Halide Hydrates

APPLICATIONS TO INORGANIC MATERIALS 1. Alkaline Earth Halide Hydrates 

Figurt 4.8. Quasi-isotherTnal-quasi-isobaric dehydration of CaBr2 6H20 in different sample holders (61). 

Paulik ex al. i62) also found that anhydrous CaBr2 decomposed completely in an oxygen atmosphere between 500-1000°C with the formation of CaO and Br2. In a nirrogen atmosphere, 3% of the compound was evolved due to sublimation at temperatures between 700 and 1000°C. 

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The alkaline earth halide hydrates and related salts have been studied by TG and other thermal techniques under a variety of atmospheric and instrumental conditions. Using the quasi-isothermal and quasi-isobaric techniques in different types of sample holders, Paulik et al. (61) found that various hydrate stoichiometries could be obtained. As shown in Figure 4.8, the inflection points in curve (/) indicate the presence of CaBr2-2H20 and CaBr2 H20. In curves (2)-(4), the inflection points correspond 10 CaBr2-3H20 and... 

With some of the alkali- and alkaline-earth halides, ammonia forms complexes that, in their general behaviour, strongly resemble the hydrates. Since neither the positive nor the negative ions have unoccupied orbitals available for bond formation, it has to be assumed that in these ammoniates the ammonia is bonded by the electrostatic attraction of the ions of the halide on the dipole of the ammonia molecule. 

Water, in its reaction with the alkali- and alkaline-earth metals, resembles ammonia, but the complexes with the halides of the platinum metals are different. The water molecule has two lone pairs of electrons, but these pairs seem to be less active in complex formation. There are many cases in which from the magnetic moment it can be concluded that the hydrates are still ionic, whereas in the corresponding NH3 complex there is covalency, the NH3 molecules sharing their lone electron-pairs with the metal atom. 

A large number of compounds used as catalysts in acid-ion lactam polymerization are known. These include alkalis, alkali-earth metals, hydrates, Grignard reagents, lithium oxide, various hydroxides and carbonates, sulfates, halides, sodium zincate, alkaline salts of different acids, i.e., compounds that cause the formation of lactam acid ion in the reactive medium. The mechanism of polymerization in the presence of sodium-lactam- salt compounds is largely known. 

Thus, it is the contribution of the water-field stabilization energy to the heat of hydration that is the special feature distinguishing transition-metal ions from the alkali-metal, alkaline-earth-metal, and halide ions in their interactions with the solvent. 

A wealth of information on the reduction of metal ions in aqueous solutions has been obtained and a compilation was published in 1988 [20], However, alkali or alkaline earth metal ions such as Li Na or cannot be reduced by the hydrated electron in aqueous solution but can form an ion pair with the solvated electron in polar liquids. Among the various reactions of the solvated electron, the reduction of halogenated hydrocarbons is often used in radiation chemistry to produce well-defined radicals because of the selective cleavage of the carbon-halogen bond by the attack ofthe solvated electron. This reaction produces the halide ion and a carbon-centered radical, and is of great interest for environmental problems related to the destruction of halogenated organic contaminants in water and soil [21,22]. 

Barium is a member of the alkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely allied series in which the chemical and physical properties of the elements and their compounds vary systematically with increasing size, the ionic and electropositive nature being greatest for barium (see Calcium and calcium alloys Calcium compounds Strontium and STRONTIUM COMPOUNDS). As size increases, hydration tendencies of the crystalline salts increase solubilities of sulfates, nitrates, chlorides, etc, decrease (except fluorides) solubilities of halides in ethanol decrease thermal stabilities of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

Lyotropic numbers N o, Table 5.1, were assigned to ions in the 30s of the last century by Buchner and Voet (Buchner et al. 1932 Voet 1937a, 1937b) according to their effects on colloidal systems. The lyotropic series has nowadays been to some extent superseded by the Hofmeister series, with which it is taken to be practically synonymous, but it is not so exactly. For the alkali metal cations and the halide anions the lyotropic numbers obtained from colloidal phenomena are linearly related to their enthalpies of hydration. Voet (1937a) concluded that the lyotropic series are simply related to the electric field strengths of the ions. Note that the Myo values for the alkali metal cations are not commensurate with those of the alkaline earth cations and with those of the anions. 

The interaction of D-glucose with hydrated alkaline-earth metal halides has been studied in solution, and complexes of the type Mg(D-glucose)Xa.4HaO, Ca(D-glucose)Xa.4HaO, and Ca(D-glucose)aXa.4HaO, where X=C1 and Br , have been isolated, and characterised by means of F.T.-I.R. and H-NMR spectroscopy. X-ray powder diffraction, and molar conductivity measurements. ... 

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