Novel Ionophores for Barium‐Selective Electrodes: Synthesis and Analytical Characterization

Abstract

A novel way of synthesis is developed for the Ba 2 + selective neutral Ionophore 2a: 2,2'-[1,2-phenylenebis(oxyethane-2,1-diyloxy)]bis(N-benzyl-N-phenylacetamide) and its methyl (2b), buthyl (2c), and hexyl (2d) derivatives. Ba 2 + selective electrodes based on Ionophores 2a-d are compared with those with commonly used Ionophore 1: N,N,N',N'-tetracyclohexyl-oxybis(o-phenyleneoxy) diacetamide. It is shown that Ionophores 2a-d, particularly 2b, are superior for measurements of Ba 2 + in the presence of Ca 2 + , and in acidic solutions. Segmented sandwich membrane studies suggest formation of complexes IL 2 2 + for Ba 2 + , Ca 2 + and Mg 2 + ions with Ionophore 2b, while H + ions apparently form complexes H 2 L 2 + . The values of the complex formation constants are consistent with the selectivity coefficients.

Insights into the Coordination Ability of Siloxanes Employing Partially Silicon Based Crown Ethers: A Comparative Analysis of s-Block Metal Complexes

“…In the presence of LiOTf (OTf = CF 3 SO 3 − ), a remarkable downfield shift is observed from 0.9 to 9.4 ppm in deuterated dichloromethane. 11 At this point, it can be summarized that the 29 Si NMR experiment is a very good indicator of the strength of the interaction of a Lewis acid with the siloxane backbone as the shift is very sensitive toward coordination. A quite similar ligand behavior to that observed in 2 is also expected for the magnesium cation (r i [Mg 2+ ] CN6 = 72 pm; CN = coordination number) 24 which is in a diagonal relationship with lithium (r i [Li + ] CN6 = 72 pm).…”

“…Solvents were dried and freshly distilled before use. Compound 7 and the organic fragment of 1 were synthesized using methods described in the literature. , Alkali and alkaline earth metal salts were dried in vacuo and handled under an argon atmosphere using a glovebox of MBraun-type. NMR spectra were recorded on different Bruker spectrometers including an AV III HD 300 MHz or an AV III 500 MHz.…”

“…Taking all these observations into account one can conclude that a perfect match of a hard cation with the crown ether cavity can make siloxane oxygen atoms available for effective coordination. As the coordination chemistry of hard group 1 and 2 metal ions turned out to be successful, the 29 Si NMR chemical shifts are summarized in Figure 6. As can be seen here, the shifts are highly sensitive toward coordination, and the choice of the Lewis acid and ligand can reveal very different coordination modes which are very well-represented in solution.…”

“…13,14 Especially group 2 metal ions seem to readily form stable complexes with ligands bearing a Si−O moiety. 13,15,16 The group of Harder very recently introduced the synthesis and structure of the 29 Si NMR experiments. 17 While the coordination chemistry of ligands bearing a single O−Si−Si− O linkage has advanced quite well, the coordination chemistry of ligands bearing two or more adjacent disilane units (see Scheme 1d) is at an early stage.…”

“…With [Li(1,2,4,5-tetrasila [12]crown-4)OTf] (OTf = CF 3 SO 3 − ) only one example is known so far in which the uncommon binding motif (Si 2 Me 4 ) 2 O•••LA (LA = Lewis acid) could be observed. 11 The ligand shows a fair complexation ability, but additional experimental data is necessary in order to understand the coordination chemistry of a ligand with the O−Si 29 Si NMR chemical shift.…”