Showing papers on "15-Crown-5 published in 1982"
TL;DR: In this paper, the stability of the complexes appears to depend primarily on the relative sizes of the metal ions and of the internal cavity of each macrocycle, and is influenced by solvation effects.
Abstract: The complexation in anhydrous proplene carbonate of the lanthanide ions by various macrocylic polyethers featuring from four to ten oxygen atoms has been investigated by a competitive potentiometric technique with lead(II) or thallium(I) as auxilliary ions. The stability of the complexes appears to depend primarily on the relative sizes of the metal ions and of the internal cavity of each macrocycle. It depends also on the rigidity of the ligands and is influenced by solvation effects. The small ligands 12-crown-4 (1) and 15-crown-5 (2) exhibit a similar behavior: they form 1:2 lanthanide complexes, the stability of which decreases with decreasing ionic radius despite the higher charge density of the metal ions. The presence of an electron-withdrawing phenyl group, as in 4-tert-butylbenzo-15-crown-5 (3), leads to a strong reduction of the stability constants. A maximum stability of 1:1 complexes of 3 is found at Nd(III) while a marked minimum is observed at Gd(III) in the complexation curve of dibenzo-30-crown-10 (5). Divalent samarium and ytterbium are more strongly coordinated than the corresponding trivalent ions by the crown ethers 1-5. The larger divalent ions fit better into the internal cavity of 5 and they form stable 1:2 sandwich complexes with 1 and 3. Themore » properties of the complexes described in the present work are completely different from those reported so far in the case of noncylic ligands.« less
50 citations
TL;DR: In this article, the authors used naphtho-15-crown-5 polyvinyl chloride (PVC) membrane electrodes with a Nernstian response in the range 10 -1 -10 -5 M.
37 citations
35 citations
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26 citations
TL;DR: The crystal structure of the EAA sodium enolate 15 crown 5 complex (E−Na+−15C5) was described and compared with the E−K+−18C6 structure already published as mentioned in this paper.
Abstract: The crystal structure of the ethylacetoacetate (EAA) sodium enolate – 15 crown 5 complex (E−Na+–15C5) is described and compared with the E−K+–18C6 structure already published. Both entities are con...
22 citations
TL;DR: In this paper, the first compelling evidence for intramolecular sidearm involvement in sodium and potassium cation complexation by carbon-pivot lariat ethers is presented.
21 citations
TL;DR: In this paper, the formation constants for 1:1 complexes of benzo-15-crown-5 (B15C5) with alkali metal ions at 25 °C, and the enthalpy and entropy changes (ΔS) of the K+−B15c5 complex in propylene carbonate (PC) have been determined conductometrically.
Abstract: The formation constants (KML+) for 1:1 complexes of benzo-15-crown-5 (B15C5) with alkali metal ions at 25 °C, and the enthalpy (ΔH) and entropy changes (ΔS) of the K+–B15C5 complex in propylene carbonate (PC) have been determined conductometrically. The KML+ series of B15C5 for the alkali metal ions are given in the order Na+>Li+>K+>Rb+>Cs+. The selectivity tendency of B15C5 for the alkali metal ions is consistent with the size-fit concept, however, B15C5 shows poor selectivity. Both the ΔH and ΔS values for the complexation reaction of B15C5 with K+ are negative. In the cases of Na+, K+, Rb+, and Cs+, the size of the moving entity in PC is larger for the B15C5 complex than for the corresponding alkali metal ion, while, in the case of Li+, that is completely the reverse.
17 citations
TL;DR: Certain host molecules having electrondonating sidearm derived from 15-crown-5 were found to display excellent Na+/K+ selectivity.
Abstract: Certain host molecules having electrondonating sidearm derived from 15-crown-5 were found to display excellent Na+/K+ selectivity.
16 citations
6 citations
TL;DR: In this paper, a stable galvinoxyl derivative (1) of benzo-15-crown-5 was prepared and the complex formation between the spin labeled crown ether 1 and the alkali metal and ammonium salts was studied by the ESR technique.
Abstract: A stable galvinoxyl derivative (1) of benzo-15-crown-5 was prepared and the complex formation between the spin labeled crown ether 1 and the alkali metal and ammonium salts was studied by the ESR technique. Existence of the (2:1) complex of 1 with potassium, rubidium, and ammonium salts was confirmed by the observation of the triplet ESR spectra in ethanol rigid matrix at 77 K. Essentially the same g- and D-tensor values are observed for all the (2:1) complexes, indicating similar conformation of the ligand molecule 1. The zero-field splitting parameters (D and E) are calculated on the basis of the spin distribution of 1 and the assumed molecular structures for the (2:1) complex. By comparing the observed D and E parameters with the calculated ones, the structure of the (2:1) complex in ethanol rigid matrix is discussed. On the other hand, the sodium complexes of 1 show a slightly asymmetric single line, suggesting the (1:1) complex formation between 1 and the sodium salts. No anions (SCN−, Br−, and I−) h...