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New Terpyridine-Containing Macrocycle for the Assembly of Dimeric Zn(II) and Cu(II) Complexes Coupled by Bridging Hydroxide Anions and π-Stacking Interactions
journal contribution
posted on 2004-08-09, 00:00 authored by Carla Bazzicalupi, Andrea Bencini, Emanuela Berni, Antonio Bianchi, Andrea Danesi, Claudia Giorgi, Barbara Valtancoli, Carlos Lodeiro, João Carlos Lima, Fernando Pina, M. Alexandra BernardoThe synthesis of the new terpyridine-containing macrocycle 2,5,8,11,14-pentaaza[15](6,6‘ ‘)cyclo(2,2‘:6‘,2‘ ‘)terpyridinophane (L) is reported. The ligand contains a pentaamine chain linking the 6,6‘ ‘ positions of a terpyridine
unit. A potentiometric, 1H NMR, UV−vis spectrophotometric and fluorescence emission study on the acid−base
properties of L in aqueous solutions shows that the first four protonation steps occur on the polyamine chain,
whereas the terpyridine nitrogens are involved in proton binding only at strongly acidic pH values. L can form both
mono- and dinuclear Cu(II), Zn(II), Cd(II), and Pb(II) complexes in aqueous solution. The crystal structures of the
Zn(II) and Cd(II) complexes {[ZnLH]2(μ-OH)}(ClO4)5 (6) and {[CdLH]2(μ-Br)}(ClO4)5·4H2O (7) show that two
mononuclear [MLH]3+ units are coupled by a bridging anion (OH- in 6 and Br- in 7) and π-stacking interactions
between the terpyridine moieties. A potentiometric and spectrophotometric study shows that in the case of Cu(II)
and Zn(II) the dimeric assemblies are also formed in aqueous solution containing the ligand and the metals in a
1:1 molar ratio. Protonation of the complexes or the addition of a second metal ion leads to the disruption of the
dimers due to the increased electrostatic repulsions between the two monomeric units.
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dimeric assembliesligandpolyamine chainpotentiometricOHmetal ionfluorescence emission studysolution1 H NMRproton bindingprotonation stepsmonomeric unitspentaamine chainUVBridging Hydroxide Anionsterpyridine unitZnM L HCuacidic pH valuescrystal structuresterpyridine moietiescomplexterpyridine nitrogens
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