Potentiometry of the Dioxa–Triaza Macrocyclic Complexes as Receptors for First-Row Transition and Lanthanide Metals
✍ Scribed by Ki-Young Choi; Yong-Ill Lee; Hee-Sup Kil; Dong-Won Kim; Yong-Soon Chung; Chang-Suk Kim; Choon-Pyo Hong; Wonbo Sim
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 108 KB
- Volume
- 53
- Category
- Article
- ISSN
- 0026-265X
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✦ Synopsis
The protonation constants and the complex stability constants of 1,7-dioxa-4,10,13triazacyclopentadecane-4,10,13-tripropionic acid (N-pr 3 [15]ane N 3 O 2 ) with some first-row transition metals (Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ ) and lanthanide metals (Ce 3+ , Eu 3+ , Gd 3+ , and Yb 3+ ) have been determined at 25°C in aqueous 0.1 M NaClO 4 solution by a potentiometric method. The results obtained are compared to those obtained for a similar ligand, 1,7-dioxa-4,10,13triazacyclopentadecane-4,10,13-triacetic acid (N-ac 3 [15]ane N 3 O 2 ), which has been previously reported. The stability constants of lanthanide complexes of N-pr 3 [15]ane N 3 O 2 ) increase with the decreasing ionic radii of Ln 3+ . The order of metal binding strengths with N-pr 3 [15]ane N 3 O 2 for the first-row transition metals was Ni 2+ > Zn 2+ > Co 2+ > Cu 2+ , which is obviously reversed from that with N-ac 3 [15]ane N 3 O 2 , Cu 2+ > Co 2+ ס Zn 2+ > Ni 2+ . The tendency to the reversal of this trend is rationalized and discussed in terms of the matching of the ligand properties with metal ion characteristics by the use of molecular mechanic calculations. These facts suggest that the structure of a polyoxa-polyaza macrocyclic compound can be preorganized by modifying the pendant arms to achieve unique selectivity for a particular metal cation.