Dicarbollide anion

Figure 3.116 The optimized structure of the dicarbollide anion, C2B9Hn2, with the atom numbering employed herein.

Figure 3.117 The bent ctbc ( ttbc ) rim bond (see Eq. (3.269) in the text) in the dicarbollide anion, C2B9H112-.

Aside from their extensive use in metaUacarborane chemistry, the dicarbollide anions are important intermediates in the synthesis of other carborane compounds. For example, aqueous ferric chloride oxidation of the [7,8-C2B9H1 L] anion results in the 10-vertex cage nido-5,6-C2BgH12 (118) and the aqueous chromic acid oxidation of [7,9-C2B9H1J yields rcz //0-l,3-C2B7H13 [17653-38-2] (29). 

Rais, J., Griiner, B. 2004. Extraction with metal bis(dicarbollide) anions Metal bis(dicarbollide) extractants and their applications in separation chemistry. In Ion Exchange and Solvent Extraction, A Series of Advances Vol. 17. Marcus, Y., SenGupta, A.K., Marinsky, J.A. Eds. Marcel Dekker, New York, pp. 243-334. 

In mixtures with the hydrophobic dicarbollide anion, the extraction of Ca, Sr, and Ba by calixarenes with oxygen donor atoms improves, allowing the separation from alkali ions.131 The competition by alkali ions is lower than in crown ether extraction systems. Separation factors S with CA2 in nitrobenzene are log S = 7 (Ca), 5.5 (Sr), and 5.4 (Ba). 

To increase the distribution ratios, a solution of lithium nitrate 1M was used. This salt, which has a common anion with europium and americium to be extracted but a cation which is usually negligibly extracted by other calixarenes, should increase the distribution ratios according to the relation Du = A (JU "[N03- ". It seems that these calixarenes, as several nitrogen ligands do, present a certain affinity for this lithium cation. The lipophilic dicarbollide anion (BrCosan), which is known to facilitate cation extraction, was implemented and led to a strong increase of the extraction of cations from 10 3 M HN03 solutions. Under these conditions, only thiopicolinamide was not able to significantly extract trivalent actinides.187... 

Coupez, B., Wipff, G. The synergistic effect of cobalt-dicarbollide anions on the extraction of M3+ lanthanide cations by calix[4]arenes A molecular dynamics study at the water- oil interface. C.R. Chimie (2004) 7(12), 1153-1164. 

EXTRACTION WITH METAL BIS(DICARBOLLIDE) ANIONS METAL BIS(DICARBOLLIDE) EXTRACTANTS AND THEIR APPLICATIONS IN SEPARATION CHEMISTRY ]iH Rais and Bohumir Griiner... 

Coupez, B., Wipff, G. (2004), The Synergistic Effect of Cobalt-dicarbollide Anions on the Extraction of M Lanthanide Cations by Calix[4]arene-CMPO ligands a Molecular Dynamics Study at the Water-"oil" Interface, C. R. Chimie Acad. Sc. Paris, in press. 

Skeletal Rearrangements following Electrophilic Alkylation of 7,8- and 7,9-Dicarbollide Anions (A Review)... 

By the time the alkylation studies were started, the reactivity of the dicarbollide anions toward electrophilic agents had been studied mainly on insertion reactions of boron, or heteroatom, or transition metal into the place of the missing vertex of the icosahedron, restoring its structure. A broad area of metallocarboranes was developed as a result of these studies, which was the subject of many articles and reviews. 

Figure 1. Reaction of 7,8-dicarbollide anion with methyl iodide.

U(C2B9Hii)2Cl2] is the first reported actinide metallocarbaborane complex. It results from the reaction of UCU in THF with the 1,2-dicarbollide anion. The crystal structure shows the U atom to have approximately tetrahedral geometry, with pentahapto-dicdtrhoUide ligands (Figure 13). ... 

Regarding the possible adsorption of lipophilic ions, different studies have been performed to see whether these lipophilic ions are preferentially located at the interface. For example, Chevrot et al. have studied the widely used cobalt bis(dicarbollide) anions [(B9C2HgCl3)(2)Co], CCD-, at the water-nitrobenzene [29] and at the water-chloroform interface [30]. This anion adsorbs at the former and very much at the latter, acting as a surfactant despite its nonamphiphilic nature. These authors attribute the excellent extracting properties of CCD to this specific adsorption as illustrated in Figure 1.1. 

Chevrot, G., R. Schurhammer, and G. Wipff, Surfactant behavior of ellipsoidal dicarbollide anions A molecular dynamics study, J Phys Chem B, Vol. 110, (2006) p. 9488. 

The amphiphilicity is closely related to the surface activity. An accumulation of cobalt bis(dicarbollide) anions at the oil/water interface was studied by Wipff et al. using a molecular dynamics approach (Chaumont, 2004 Chevrot, 2006 Chevrot et al., 2007a,b). Experimental studies on the surface tension measurements of cobalt bis(dicarbollide) were published by Borisova (Borisova, 2004 Popov, 2001) and van Man et al. (1984). It is a well-established fact that some surface-active compounds like alkylsulfonates can form multimolecular aggregates, micelles, in aqueous solutions. The question is, whether the water-soluble salts of cobalt bis(dicarbollide) could also associate in aqueous media. Somewhat surprisingly, the detailed analysis of the self-assembly of cobaltacarboranes in aqueous solutions was only provided recently (Matejfcek, 2006), 40 years after the discovery of cobalt bis(dicarbollides) by Hawthorne (1965, 1971). 

Chevrot, G., Schurhammer, R., and Wipff, G. 2007a. Molecular dynamics study of dicarbollide anions in nitrobenzene solution and at its aqueous interface. Synergistic effect in the Eu(III) assisted extraction. Phys. Chem. Chem. Phys. 9 5928-5938. 

FIGURE 9.13 Conjugate of chlorine with two cobalt bis(dicarbollide) anions. (Adapted from V. I. Bregadze et al. Appl. Radiat. Isotop., 2009, 67, N.7-8, Supl.l, P.S101-S104.)... 

Cobalt bis(dicarbollide), commonly known as CoSan , is an example of a boron compound which serves the role of a scavenger for the extremely biotoxic Cs-137 ion produced from the nuclear wastes. Although it has long been synthesized, the importance of this particular compound has developed only recently. Cobalt bis(dicarbollide) anion and its chloroprotected form have now being nsed as extractants for high-level liquid nuclear wastes. 

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