Dioxatriazamacrocycle-N,N′,N″-triacetic Acids: Synthesis, Protonation Constants, and Metal-Complex Studies. Crystal Structure of Hydrogen [1,4-Dioxa-7,10,13-triazacyclopentadecane-7,10,13-triacetato(4)-κN7,κN11,κN13,κO7]copper(1 –) Hydrate (2 : 1) ([Cu(HL1)]⋅0.5 H2O)
✍ Scribed by M. Fátima Cabral; Rita Delgado; M. Teresa Duarte; Miguel Teixeira
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- German
- Weight
- 218 KB
- Volume
- 83
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Two new dioxatriazacyclopentadecanetriacetic acids were synthesized, i.e. 1,4-dioxa-7,10,13-triazacyclopentadecane-7,10,13-triacetic acid (1; H 3 L 1 ) and 1,4-dioxa-7,10,14-triazacyclohexadecane-7,10,14-triacetic acid (2; H 3 L 2 ). The protonation constants of these compounds and the stability constants of complexes of both ligands with the alkaline-earth metal ions, Mn 2 to Zn 2 , Cd 2 , and Pb 2 were determined by potentiometric methods at 258 in 0.10m tetramethylammonium nitrate solution. Both ligands exhibit two high-value protonation constants and two low-value ones. Only mononuclear complexes were found for both ligands with the alkaline earth metal ions, and their stability constants are surprisingly low, suggesting the involvement of only two N-atoms of the macrocycles and two carboxylate groups in the coordination to these metal ions (or a very weak interaction with all the carboxylates). Mono-and dinuclear species were found in solution for most of the divalent first-row transition-metal ions, Cd 2 , and Pb 2 . Ligand 1 (H 3 L 1 ) formed mononuclear complexes that were thermodynamically more stable, while 2 (H 3 L 2 ) stabilized the dinuclear species better due to the larger cavity size of the macrocycle. Electronic and EPR-spectroscopic studies in solution revealed that the Co 2 , Ni 2 , and Cu 2 complexes are six-coordinate, and that the three N-atoms of the macrocycles are involved in the coordination. EPR Spectra of the copper(II) dimer of 2 show resonances corresponding to the DM s 1 and DM s 2 transitions. The structure of [Cu(HL 1 )] ´0.5 H 2 O, obtained from Cu 2 and 1, was determined by singlecrystal X-ray diffraction. The complex adopts a distorted compressed trigonal-bipyramidal geometry, with the macrocycle in a folded conformation. The basal plane is formed by two N-and one O-atoms of the macrocycle backbone, and the apical positions are occupied by the other N-atom of the ring and one of the O-atoms of one carboxylate group. Electronic and EPR-spectroscopic studies show that the same complex exists in solution in a six-coordination symmetry with tetragonal elongation.