Synthesis and properties of 5-chloro-8-hydroxyquninoline-substituted azacrown ethers: A new family of highly metal ion-selective lariat ethers
- Brigham Young Univ., Provo, UT (United States); and others
New 5-chloro-8-hydroxyquinoline (CHQ)-substituted aza-18-crown-6 (4), diaza-18-crown-6 (1), diaza-21-crown-7 (2), and diaza-24-crown-8 (3) ligands, where CHQ was attached through the 7-position, and aza-18-crown-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for complexation of these CHQ-substituted macrocycles with alkali, alkaline earth, and transition metal ions were determined in absolute methanol at 25.0 {degrees}C by calorimetric titration. Two isomers, 1 and 10, which are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities toward the metal ions. Compound 1 forms very stable complexes with Mg{sup 2+}, Ca{sup 2+}, Cu{sup 2+}, and Ni{sup 2+} (log K = 6.82, 5.31, 10.1 and 11.4, respectively), but not with the alkali metal ions. Ligand 10 displays strong complexation with K{sup +} and Ba{sup 2+} (log K = 6.61 and 12.2, respectively) but not with Mg{sup 2+} or Cu{sup 2+}. The new macrocycles and their complexes have been characterized by means of UV-visible and allow an analytical determination of Mg{sup 2+} in very dilute solutions in the presence of other alkali and alkaline earth metal cations. {sup 1}H NMR spectral and X-ray crystallographic studies indicate that ligand 10 forms a cryptate-like structure when coordinated with K{sup +} and Ba{sup 2+}, which induces an efficient overlap of the two hydroxyquinoline rings. Such overlapping forms a pseudo second macroring that results in a significant increase in both complex stability and cation selectivity.
- DOE Contract Number:
- FG02-86ER13463
- OSTI ID:
- 450690
- Journal Information:
- Inorganic Chemistry, Vol. 35, Issue 25; Other Information: PBD: 4 Dec 1996
- Country of Publication:
- United States
- Language:
- English
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