Protonation and coordination properties towards Zn(ii), Cd(ii) and Hg(ii) of a phenanthroline-containing macrocycle with an ethylamino pendant arm

Carla Bazzicalupi, Andrea Bencini, Emanuela Berni, Antonio Bianchi, Lucia Borsari, Claudia Giorgi, Barbara Valtancoli, Carlos Lodeiro, João Carlos Lima, A. Jorge Parola, Fernando Pina

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

Protonation and Zn(ii), Cd(ii) and Hg(ii) coordination with the ligand 5-aminoethyl-2,5,8-triaza-[9]-10,23-phenanthrolinophane (L2), which contains an aminoethyl pendant attached to a phenanthroline-containing macrocycle, have been investigated by means of potentiometric,1H NMR and spectrofluorimetric titrations in aqueous solutions. The coordination properties of L2 are compared with those of the ligand 2,5,8-triaza-[9]-10,23-phenanthrolinophane (L1). Ligand protonation occurs on the aliphatic amine groups and does not involve directly the heteroaromatic nitrogens. The fluorescence emission properties of L2 are controlled by the protonation state of the benzylic nitrogens: when not protonated, their lone pairs are available for an electron transfer process to the excited phenanthroline, quenching the emission. As a consequence, the ligand is emissive only in the highly charged [H3 L2]3+ and [H4 L2]4+ species, where the benzylic nitrogens are protonated. Considering metal complexation, both [ML1]2+ and [ML2]2+ complexes (M = Zn(ii) and Cd(ii)) are not emissive, since the benzylic nitrogens are weakly involved in metal coordination, and, once again, they are available for quenching the fluorescence emission. Protonation of the L2 complexes to give [MHL2]3+ species, instead, leads to a recovery of the fluorescence emission. Complex protonation, in fact, occurs on the ethylamino group and gives a marked change of the coordination sphere of the metals, with a stronger involvement in metal coordination of the benzylic nitrogens; consequently, their lone pairs are not available for the process of emission quenching.

Original languageEnglish
Pages (from-to)591-597
Number of pages7
JournalJournal of the Chemical Society. Dalton Transactions
Volume4
Issue number4
DOIs
Publication statusPublished - 9 Feb 2004

Keywords

  • Luminescence, fluorescence
  • Macrocycles
  • Sensors, receptors
  • Stability constants
  • Supramolecular chemistry

Fingerprint

Dive into the research topics of 'Protonation and coordination properties towards Zn(ii), Cd(ii) and Hg(ii) of a phenanthroline-containing macrocycle with an ethylamino pendant arm'. Together they form a unique fingerprint.

Cite this