Metal complexes of a tetraazacyclophane: Solution and molecular modelling studies

2003

An alternative synthetic approach to yield the compound 2,3,5,6,8,9,11,14-octahydrobenzo[l][1,4,7,10]tetraazacyclotetradecine (bz[14]N4) is presented. The protonation constants of bz[14]N4 and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ were determined in H2O at 25 °C with ionic strength 0.10 mol dm3 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 NHCl 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]N4 confers a coordination behaviour intermediate between that of cyclam and cyclen.

Autores da comunidade :

• 

  R

  Rita Virgínia Delgado António

  ist10884

• 

  M

  Maria Paula Cordeiro Crespo Cabral Campello Aboim de Barros

  ist25375

  Afiliações e fontes

  De: orcid

  ID: 10910743

  De: cienciavitae

  ID: 616726

AO - Versão original do autor

Dalton Transactions

1852

1860

9

10.1039/b301033c

chemical-sciences - Química

eng - Inglês

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