Utilize este identificador para referenciar este registo: http://hdl.handle.net/10451/21375
Título: 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)-kappa N-7,kappa N-11,kappa N-13,kappa O-7]copper(1-) hydrate (2
Autor: Cabral, MF
Delgado, R
Duarte, MT
Teixeira, M
Palavras-chave: Chemistry, Multidisciplinary
Data: 2000
Citação: HELVETICA CHIMICA ACTA. - Vol. 83, n. 4 (2000), p. 702-721
Resumo: Two new dioxatriazacyclopentadecanetriacetic acids were synthesized, i.e 1,4-dioxa-7,10,13-triazacyclopentadecane-7,10,13-triacetic acid (1: H3L1) and 1,4-dioxa-7,10,14-triazacyclohexadecane-7,10,14-triacetic acid (2: H3L2). The protonation constants of these compounds and the stability constants of complexes of both ligands with the alkaline-earth metal ions. Mn2+ to Zn2+, Cd-2. and Pb2+ were determined by potentiometric methods at 25 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 Pb2+. Ligand 1 (H3L1) formed mononuclear complexes that were thermodynamically more stable, while 2 (H3L2) stabilized the dinuclear species better due to the larger cavity size of the macrocycle. Electronic and EPR-spectroscopic studies in solution revealed that the Co2+, Ni2+. and Cu2+ complexes are six-coordinate, and that the three N-atoms of the macrocycles are involved in the coordination. EPR Spectra or the copper(II) dimer of 2 show resonances corresponding to the Delta M-s = 1 and Delta M-s = 2 transitions. The structure of [Cu(HL1)] 0.5 H2O, obtained from Cu2+ and 2, was determined by single-crystal 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.
URI: http://hdl.handle.net/10451/21375
ISSN: 0018-019X
Aparece nas colecções:FF - Produção Científica 2000-2009

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