Complexes of barium

Fig. 1 Absorption scanning curve of the alizarin complexes of barium (1), strontium (2), calcium (3), magnesium (4) and beryllium cations (5). The amounts appUed were 2 pg in each case.

There is an appreciable difference between the stability constants of the CDTA complexes of barium (log K = 7.99) and calcium (log K = 12.50), with the result that calcium may be titrated with CDTA in the presence of barium the stability constants of the EDTA complexes of these two metals are too close together to permit independent titration of calcium in the present of barium. 

Figure 60 The structure of the crown ether complex of barium diphenylmethanide 116 (the dashed line is to a contact at 3.39 A). 

An interesting method of synthesis has been employed to produce MgBr2-2HMPA the ligand is reacted with EtMgBr in Et20 to produce unstable crystals of the product.30 The pathway presumably is by displacement of the Grignard equilibrium. A complex of barium p-nitrobenzoate with DMSO has been synthesized and actually separated from DMSO with water present in the system.130... 

H. Sitzmann, M. D. Walter and G. Wolmershauser, A triple-decker sandwich complex of barium. Angew. Chem. Int. Ed. 41, 2315-16 (2002). 

Figure 12 The environment of Ba in the triethanolamine complex of barium acetate...

At this stage the solvent is 40% ethanol, the pH is acidic, and the color is light orange. Complexation of barium by methylthymol blue is not a rapidly reversible process (21) indeed sulfate ion will not readily remove barium from its methylthymol blue complex in basic solution. To avoid this problem the reagent is initially acidic, allowing only negligible chelation of the barium until the precipitation of the barium sulfate is completed. 

Hatanpaa T, Vehkamaki M, Mutikainen I, Kansikas J, Ritala M, Leskela M. Synthesis and characterisation of cyclopentadienyl complexes of barium precursors for atomic layer deposition of BaTiOs. Dalton Trans 2004 181-8. 

The reduced mobility of radium in comparison with uranium is explained by the solubility difference between the two elements, which occur in nature as sulphates and carbonates at 18°C radium sulphate = 1.410" g/1 uranyl sulphate = 205 g/1 radium carbonate is insoluble and uranyl carbonate = 60g/l. With the acidity and alkalinity of water, however, radium solubility changes. The radium content of water also depends on the salt concentration of certain elements—mainly alkaline chloride (radium replaces sodium). Radium precipitates with complexes of barium (S04Ba) and with calcium carbonates (travertine). Radium is also fixed by clay, organic matter, iron and manganese hydroxides. 

Finally, Davidson and coworkers disclosed [ ONNO Ba]3(THF)2 (79), an unusual trinuclear complex of barium containing three dianionic, tetradentate ONNO diamino-hw(phenolate) ligands (Fig. 25) [98]. Complex 79 promoted... 

These experimental electrodes with surfactants incorporated into the membranes can be used to monitor the titration of nonionics (as their Ba complexes) with tetraphenylborate (133). Ivanov and Pravshin report that an electrode suitable for determination of nonionics can be made from a membrane of plasticized PVC containing either cetylpyrid-inium dodecylsulfonate or the complex of barium and tetraphenylborate ions with a nonionic (134). These electrodes also respond to ionic surfactants and respond much better to tetraphenylborate than to nonionic surfactants. Thus, they are most useful for monitoring the end point of a titration of the barium complexes of nonionics with tetraphenylborate. Ionic surfactants interfere in the titration. 

The following table lists the molar absorptivities for the Arsenazo complexes of copper and barium at selected wavelengths. " Determine the optimum wavelengths for the analysis of a mixture of copper and barium. 

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

At last, barium and calcium complexes of phosphonium bifluorenylide 19 was obtained from the corresponding phosphonium iodide (Scheme 12). The anion displays weak nucleophilicity toward both cations which prefer to coordinate with neutral oxygen of THF and with iodide. Located outside the coordination sphere of the metals, it represents thus the first example of uncomplexed phosphonium diylide [59]. 

Thennodynamic inhibitors are complexing and chelating agents, suitable for specific scales. For example, for scale inhibition of barium sulfate, common chemicals are ethylenediaminetetraacetic acid (EDTA) andnitrilotriacetic acid. The solubility of calcium carbonate can be influenced by varying the pH or the partial pressure of carbon dioxide (CO2). The solubility increases with decreasing pH and increasing partial pressure of CO2, and it decreases with temperature. 

Radiologic and/or endoscopic procedures are usually required to objectively document the presence of ulcers. Barium studies have a high sensitivity and are considered first-line tests to radiographically document an ulcer. However, the cost and complexity of all of these tests has led to the promotion of an early empiric treatment strategy for patients at low risk for PUD-related sequelae (e.g., malignancy). An empiric treatment strategy is appropriate for patients less than 50 years of age who have mild or intermittent epigastric symptoms and no evidence of PUD-related systemic symptoms or complications. 

The recognition of barium containing crown ether bridged chiral Schiff base zinc complex [44] with the rigid bidendate guest 1,4-diazobicyclo-[2,2,2]octane (DABCO) was studied by aH NMR titration.107... 

Polymer Preparation. A more recent modification in the molecular structure of styrene-butadiene copolymers has been obtained with the discovery of a new catalyst system (6). The catalyst consists of a barium t-alkoxide-hydroxide salt together with a complex of dialkylmagnesium and trialkylaluminum. 

The use of sterically bulky ligands to provide kinetic stability to compounds of the heavier group 2 elements has become widely practiced, and has facilitated the synthesis of diorganyl complexes of various types. Advances in the organometallic chemistry of bonded compounds of calcium, strontium, and barium have been reviewed. 

The interactions of (212) and related species with monovalent and divalent metal cations have been studied by nmr spectroscopy (Lehn Simon, 1977). The study indicated that sequential formation of mono-and di-cation complexes occurs (see [4.7]). These studies, and especially a 13C nmr study of the 1 1 complex of (212) with barium nitrate, suggest that the 1 1 species are unsymmetrical with the metal ion being contained in one of the azacrown cavities. Nevertheless, the nmr data also indicate that these 1 1 species undergo internal cation exchange between the respective azacrown sites. This intramolecular dynamic behaviour serves... 

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