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Metal complexes of a tetraazacyclophane: solution and molecular modelling studies

Antunes, P., Campello, P.M., Delgado, R., Drew, M.G.B., Felix, V. and Santos, I. (2003) Metal complexes of a tetraazacyclophane: solution and molecular modelling studies. Dalton Transactions (9). pp. 1852-1860. ISSN 1364-5447

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To link to this item DOI: 10.1039/b301033c

Abstract/Summary

An alternative synthetic approach to yield the compound 2,3,5,6,8,9,11,14-octahydrobenzo[1][ 1,4,7,10]tetraazacyclotetradecine (bz[14]N-4) is presented. The protonation constants of bz[14]N-4 and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ were determined in H2O at 25degreesC with ionic strength 0.10 mol dm(-3) in KNO3 and they were compared with structurally related macrocycles cyclam (1,4,8,11-tetraazacyclotetradecane) and cyclen (1,4,7,10-tetraazacyclododecane). These studies indicate that only 1 : 1 ( M : L) species are formed in solution, and the ligand exhibits a high affinity for larger ions such as Cd2+ and Pb2+. The X-ray study of [bz[14]N4H3](3+) shows that an inclusion compound with a chloride counter-anion is formed through NH...Cl hydrogen bonds. Spectroscopic data in solution ( electronic and NMR spectra) showed that the macrocycle adopts a planar arrangement upon metal complexation. Molecular mechanics calculations reveal that in spite of the presence of the benzene ring in the macrocyclic framework this ligand can encapsulate metal ions with different stereo-electronic sizes in square planar arrangements. Our results indicate that the presence of the benzene ring in the backbone of the bz[14]N-4 confers a coordination behaviour intermediate between that of cyclam and cyclen.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
ID Code:10969
Uncontrolled Keywords:TETRA-AZA MACROCYCLES, CAMBRIDGE STRUCTURAL DATABASE, ION SIZE SELECTIVITY, X-RAY-DIFFRACTION, NICKEL(II) COMPLEXES, COPPER(II) COMPLEXES, CHELATE RING, CRYSTAL-STRUCTURES, LIGANDS, MECHANICS
Publisher:Royal Society of Chemistry

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