Premium
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)‐ κ N 7 , κ N 11 , κ N 13 , κ O 7 ]copper(1 –) Hydrate (2 : 1) ([Cu(HL 1 )]⋅0.5 H 2 O)
Author(s) -
Cabral M. Fátima,
Delgado Rita,
Duarte M. Teresa,
Teixeira Miguel
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(20000412)83:4<702::aid-hlca702>3.0.co;2-6
Subject(s) - chemistry , protonation , tetramethylammonium , electron paramagnetic resonance , crystallography , carboxylate , potentiometric titration , stability constants of complexes , ligand (biochemistry) , inorganic chemistry , metal ions in aqueous solution , metal , dimer , hydrogen bond , crystal structure , stereochemistry , ion , molecule , organic chemistry , receptor , biochemistry , physics , nuclear magnetic resonance
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 25° in 0.10 M 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 Δ M s =1 and Δ M s =2 transitions. The structure of [Cu(HL 1 )]⋅0.5 H 2 O, obtained from Cu 2+ and 1 , 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.