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Synthesis and Characterization of Acyclic and Cyclic Azabridged Ligands Incorporating 2,2'-Bipyridine Subunits and Their Complexes With Copper(II), Cobalt(II), and Nickel(II)

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Author(s): Antonino Mamo | Andrea Pappalardo

Journal: Molecules
ISSN 1420-3049

Volume: 8;
Issue: 7;
Start page: 521;
Date: 2003;
Original page

Keywords: Transition metal complexes | bipyridine derivatives | polydentate aza-ligands | macrocycles | dynamic NMR

ABSTRACT
The synthesis of a series of N,N'-disubstituted acyclic (AL) and cyclic (CL) aza-bridged ligands incorporating 2,2-pipryidine subunits is described. 1H-NMR and IR spectral data support the proposed ligand structures. Dynamic 1H-NMR studies on diurea and diamide derivatives point to the presence of slowly interconverting conformers on the 1H-NMR time-scale, owing to N−H···N hydrogen bonding and/or a restricted rotation around the amide bonds. The ligands synthesized form 1:1 complexes with divalent transition metal ions. Upon complexation, bis-ester derivatives AL5 and CL5 undergo a metal-induced hydrolysis of the ester groups to carboxyl functions, which act as additional binding sites for the metal ion, as well as hydrogen-bonding donor-acceptor binding site to produce dimeric complexes.