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  • 1
    Electronic Resource
    Electronic Resource
    Determination of complex stabilities with nearly insoluble host molecules. Part I. Spectrophotometric detection (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 479-484 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The determination of stability constants by measuring the increase in solubility of a nearly insoluble host molecule due to complex formation with a soluble guest is discussed. If the host molecule absorbs in the UV-visible region, spectrophotometric measurements are easily performed to obtain the stability constants. The solubilities of the crown ether dibenzo-18-crown-6 and of the cryptand (222BB) in aqueous solutions and the molar absorptivities of these ligands and their complexes with alkali and alkaline earth metal cations were determined. The increase in solubility of these ligands due to complex formation with cations was used to calculate the stabilities of the complexes formed. Even under the assumption that neither the molar absorptivities nor the solubilities are known, the calculated stability constants agree very well with those obtained using the measured values of the molar absorptivities and solubilities. The accuracy of the stability constants even increases with decreasing solubility of the ligands.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070903
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of complex stabilities with nearly insoluble host molecules. Part II. Complexation of alkali and alkaline earth metal cations with dibenzo crown ethers in aqueous solution (1997)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 10 (1997), S. 781-785 
    Details
    ISSN: 0894-3230
    Keywords: complex stabilities ; alkali metals ; alkaline earth metals ; dibenzo crown ethers ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: ---An experimental method was developed to determine the stability constants with nearly insoluble ligands in homogeneous solution. This method was tested using dibenzo crown ethers, which have a very low solubility in aqueous solution. The stability constants for the complexation of alkali and alkaline earth metal cations with different dibenzo crown ethers were determined in aqueous solution. Owing to the complex formation the total concentration of the ligand in solution increases. Dibenzo crown ethers absorb in the ultraviolet spectral range, hence the increase in the ligand concentration can be easily detected. Without the knowledge of the molar absorptivities of the ligands and of the corresponding complexes and of the solubilities, the stabilities of the complexes formed can be calculated under certain assumptions. To verify these assumptions, the solubilities of the dibenzo crown ethers and the molar absorptivities were determined. The kinetics of the solubilization process of the ligands was followed by spectrophotometric measurements. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Synthese und Komplexbildung eines neuen makrocyclischen Liganden mit drei Benzimidazolin-2-on-Einheiten (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2483-2485 
    Details
    ISSN: 0009-2940
    Keywords: Macrocyclic ligand ; Benzimidazolin-2-one ; Complexation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Complex Formation of a New Macrocyclic Ligand Incorporating Three Benzimidazolin-2-one Units The new macrocyclic ligand 1 composed of three benzimidazolin-2-one-1,3-diyl and three propane-1,3-diyl building blocks has been synthesized. Complex formation constants in water involving Li+, Na+, K+, Mg2+ Ca2+, Si2+, and Ba2+ are discussed. The most stable complex is formed with Ca2+.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921251121
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  • 4
    Electronic Resource
    Electronic Resource
    Unusual Complexation Behavior of Metallomacrocycles Based on Isothiosemicarbazides with Respect to Alkali and Alkaline Earth Metal Ions: Novel 2:1 Associates (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 1089-1093 
    Details
    ISSN: 0009-2940
    Keywords: Metallomacrocycles ; Nickel complexes ; Complexation reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions between alkali and alkaline earth metal ions and nickel(II) macrocycles based on S-alkylated isothiosemi-carbazides with different crown ether cavity size were studied in propylene carbonate by spectrophotometric and calorimetric titrations. Metallomacrocycles 1 and 2 exhibit normal behavior on 1:1 complexation with alkali- and alkaline earth metal ions and resemble in this respect 15C5 and 18C6, respectively. The most stable complexes are formed by these “ligands” when the diameter of the cation and the crown ether hole have approximately the same size. The most striking feature of the complexation processes studied is the formation of 1:2 metal-ligand associates even in the case of the smallest cations. These associates are very different from “normal” crown ether sandwich complexes. In reality, the particle formed is an associate between a 1:1 complex, in which the corresponding metal ion is well accommdated inside the ligand cavity, and a second metallomacrocyclic ligand. Their formation is disfavored by enthalpic contributions. A special kind of “switch” from these associates to normal sandwich complexes takes place in the case of 1, when the cation diameter compared to hole size increases. The macrocycle 2 forms this kind of associates with all akali and alkaline earth ions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951281106
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    Paper (German National Licenses)
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