Bromide, divalency

In this section we are concerned with the properties of intrinsic Schottky and Frenkel disorder in pure ionic conducting crystals and with the same systems doped with aliovalent cations. As already remarked in Section I, the properties of uni-univalent crystals, e.g. sodium choride and silver bromide which contain Schottky and cationic Frenkel disorder respectively, doped with divalent cation impurities are of particular interest. At low concentrations the impurity is incorporated substitutionally together with an additional cation vacancy to preserve electrical neutrality. At sufficiently low temperatures the concentration of intrinsic defects in a doped crystal is negligible compared with the concentration of added defects. We shall first mention briefly the theoretical methods used for such systems and then review the use of the cluster formalism. 

In view of the synthetic applications, among carbanions stabilized by only one divalent sulfur atom, allylic thiocarbanions proved to be particularly valuable, as shown with Biellmann coupling of allylic groups, applied to an elegant synthesis of squalene from farnesyl bromide [301]. In this synthesis, the retention of the allylic double bond position and stereochemistry in both the metallation-alkylation and the desulfurization steps are noteworthy. However, the results are not always as clear-cut, and... 

In 1939 Klemm and Doll [276] prepared all the halides of divalent europium and studied the magnetic characteristics of these compounds. The magnetic susceptibilities (X g) and effective moments of the fluoride, chloride, bromide and iodide are tabulated in Table 15. Except for the... 

Ion chromatographic methods have been described for the co-determination of anions and cations in rainwater. Thus Jones and Tarter [138], using the conditions given in Table 2.19 reported determinations down to lmg L 1 of anions (chloride, bromide and sulphate) and cations (sodium, potassium, magnesium and calcium) in rainwater without converting the cations to anion complexes prior to detection [139], The technique uses a cation separator column, a conductivity detector, an anion suppressor column, and either a second conductivity detector or an electrochemical detector in sequence. The use of different eluants provides a means for the detection of monovalent cations and anions and divalent cations and anions in each of the samples. Using an eluant with a basic pH, it is possible to separate simultaneously and detect the monovalent cations (with the exception of the ammonium ion) and anions, while an eluant with an acidic pH allows for the separation and detection of divalent cations and anions. 

Divalent cations of boron have been synthesized by partial displacement of bromide from boron tribromide adducts by using substituted pyridines.1 This reaction may lead to complete substitution of bromine with sufficiently basic amines or if the reaction conditions are not properly controlled. The present synthesis avoids this side reaction by blocking the fourth coordination position on boron with hydride which is not readily displaced by amines.2 The starting material in this case is an adduct of dibromoborane, (CH3)8NBHBr2, which is readily synthesized and is described in Sec. 20B. 

Uncommon IPRs were tested recently. Polymerized acyl monoglydnate surfactant was found to be as effective as sodium dodecylsulfate for the resolution of organic amines [126]. For the analysis of pyridine-based vitamins in infant formnlas, dioc-tylsulfosuccinate produced a unique retention pattern [133], Among bizarre IPRs, tris(hydroxymethyl)aminomethane was used for the determination of cyclamate in foods. It was selected over different ion-pair reagents such as triethylamine and dibu-tylamine, based on sensitivity and time economies [134]. Hexamethonium bromide, a divalent IPR, was used successfully to separate sulfonates and carboxylates [135]. 

In addition to divalent metal cations, trivalent and tetravalent cations (i.e. ln +, Ga +, Sb +, and Sn +) were also effective as linking agents to organize [Ge4Sio]" clusters to form hexagonally ordered mesostractures. In this case, cetylpyridinium bromide was nsed as the surfactant, and formamide served as the solvent. The mesophases made with Ga + and Sb + showed intense visible photoluminescence at77K. 

In 1961 Hayes and Twidell (8) found that if calcium fluoride crystals containing trivalent thulium were irradiated with x-rays, some of the thulium was converted to the divalent state. This discovery was the first of many in the study of dilute solutions of divalent rare earth ions. Most workers prefer to study the alkaline earth fluorides since these materials are stable with respect to air and have more attractive mechanical properties than the alkaline earth chlorides, bromides, and iodides. Enough work has been carried out in these softer materials to show that reactions similar to those in the fluorides do occur. 

Divalent lanthanide ions have also been obtained in fused barium bromide by Pinch (19), who used ultraviolet radiation for the reduction. In this instance the photolysis produced bromine which was removed from the system by its volatility, and the remaining divalent lanthanide ions were stable. This reduction technique suffers from the same difficulty as the metallic reduction technique in that it is difficult to grow good crystals from this reactive melt. 

Divalent samarium is known to reduce alkyl halides. However, reductions of iodides and bromides in tetrahydrofuran (THF) require a long reaction time and chlorides are not reduced even at refluxing temperature. 

Aqueous zinc nitrate similarly treated gave the colorless crystalline bis (triaminopropane) zinc di-iodide (X) (20). An aqueous solution of sodium tetrachloroplatinate(II), Na2[PtCl4], when treated with two equivalents of the triamine, heated until clear, and then concentrated and added to aqueous sodium bromide and iodide gave the colorless bis(triamino-propane)-platinum(II) dibromide (XI X = Br), m.p. 270-271°C., and the di-iodide (XI X = I), m.p. 266-267°C., respectively. The fact that in these salts (which were sufficiently stable for recrystallization from hot water) the divalent platinum was showing the exceptional coordination number of 6—i.e., that it was coordinated to all six amino groups of the two triamine molecules, was shown by the addition of the dibromide to an excess of sodium picrate, both in cold aqueous solution, whereby only the dipicrate (XI X = C6H2N3O7) was precipitated had any amino groups remained uncoordinated, they also would have formed picrates (1928) (19). 

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