Cesium picrates

Cesium Picrate. C6H2(N02)30Cs, mw 361.01, N 11.64%, yel needles explds with moderate violence at 277—87°. It has been used to surface seed RDX charges used in expl driven magneto-hydrodynamic generators (Ref 3)... 

Fig. 4.8. Extraction of a) alkali metal nitrates and b) cesium picrate and nitrate with dibenzo-18-crown-6 (2) in CHCI3.

Figure 3. Uptake and release of cesium picrate by racemic cyclic pentamer of 6,8-dioxabicyclo[3.2.l]octan-7-one. Uptake AQ.I(tris buffer, 10 ml), [CsCl] = 1 x 10 1 M, [CsPi] = 1 X 10 4 Org.(CH2Cl2> 7 ml), [cyclic pentamer] = 1 X 10-2 M.

Charts I, II, III and IV illustrate the kinds of hosts that have been designed and synthesized and the relationships between their structures and abilities to bind lithium, sodium, potassium and cesium picrates, respectively. The differences in structural recognition by a particular guest in complexing a variety of possible hosts are measured by the differences in the - AG values listed below each structure. For lithium picrate, the values range from >23 to <6 kcal mol for sodium picrate, from 19.2 to < 6 kcal mol" for potassium picrate, from 17.1 to < 6 kcal mol" for cesium picrate, from 13.1 to < 6 kcal mol The principles of complementarity and preorganization are illustrated repeatedly in the structure-binding relationships found in these charts [3]. Only a few relationships will be discussed. 

Chart IV. - AG (kcal/mol), CDCI3, 25 °C, for complexing cesium picrate... 

The polymers most similar to polyester and polyamide are the poly(tetrahydrofuran diyls) (34 and 35) prepared by Smith and coworkers,and the polyamides 30, 32, 33, 56, 57 and prepared by Bbhmer and coworkers(see Table 1 and Fig. 13 and 26). Using a picrate extraction method both research groups reported similar ion-binding behavior. At roughly the same polymer and picrate concentrations, both polyester and polyamide are similar in their extraction capacity to Bbhmer s polyamides and to Smith s poly(tetrahydrofuran diyls). Plots of percent solute extracted versus the logarithm of the total solute concentration for lithium, potassium, and cesium picrate and polyamide show that the percentage varies widely over solute cencentration (Fig. 30-32). A similar curve for polyester and potassium picrate is Included in Fig. 31 for comparison. Its curvature is not nearly as sharp... 

In UV spectroscopy, the spectra of sodium, potassium and cesium picrate in the presence of 2d show a red shift of the absorption peak, this being dependent on the separation of the alkali ion from the picrate anion (Figure 6). 

The first studies performed at Strasbourg University by the picrate extraction method developed by Pedersen reveals a high preference of calix-crowns fixed in the 1,3-alternate conformation for cesium. In contrast to its conformational isomer, di-isopropoxy-calix[4]arene-crown-6 in the cone conformation does not extract cesium (Table 4.4). 

It must be stressed that factors such as the hydration (or solvation) of the metal ion and anion effects on the extracted complex often make it difficult to predict the order of extractability for such systems. Such factors may even influence the stoichiometry of the extracted species. Thus, the simple match of the metal to the whole concept is only of limited utility. For example, potassium, rubidium and sodium nitrates are extracted in the presence of dibenzo-18-crown-6 (2) as 1 1 1 complexes. On the other hand, cesium forms a 1 2 1 sandwich complex with this crown (metal crown nitrate) in the organic phase and this affects the extraction order for the above metal ions, with the order being dependent on ligand concentration. In contrast, for picrate as the anion the composition of the extracted cesium complex is 1 1 1 (Fig. 4.8) [27]. 

In the first instance ion transfers were investigated such as the transfer of quaternary ammonium[2-4] or cesium[5,6] cations and picrate[7], CNS, CIO i, laurylsulfate and n-octoate[8] anions. 

Inspection of Table I reveals higher 1 values for all networks when THF is replaced by dioxane, the effect being largest for sodium picrate (as much as a factor 25) and smallest for the cesium salt (about a factor 2). Complexation of crown to an extemally-complexed tight ion pair is accompanied by release of most or all of the bound solvent molecules (equation 4). The cation-solvent interaction is considerably stronger with THF than with dioxane. 

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