Cyclam derivatives containing three acetate pendant arms: synthesis, acid-base, metal complexation and structural studiesElectronic supplementary information (ESI) available: Hydrogen bond dimensions for compounds 1to 5, overall protonation and
Luís, MPL; Rita, D; Michael, GBD; Paula Bo; Vítor Fl
The ligands 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic-11-methylphosphonic acid (H5te3a1p) and 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic acid (H3te3a) were synthesized, the former one for the first time. The syntheses of these ligands were achieved from reactions on 1,4,8,11-tetraazacyclotetradecane-1,4,8-tris(carbamoylmethyl) hydroiodide (te3am·HI), and compounds (Hte3am)+, 1, and (H7te3a1p)2+, 4, were characterized by X-ray diffraction. Structures of two other compounds resulting from side-reactions, (H2te2lac)2+, 2, and (H4te2a2pOEt2)2+, 3, were also determined by X-ray diffraction. Potentiometric titrations of H5te3a1p and H3te3a were performed at 298.2 K and ionic strength 0.10 mol dm−3in NMe4NO3to determine their protonation constants. 1H and 31P NMR titrations of H5te3a1p were carried out in order to determine the very high first protonation constant of this ligand and to elucidate the sequence of protonation. Potentiometric studies of the two ligands with Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+and Pb2+metal ions performed in the same experimental conditions showed that the complexes of H5te3a1p present very high thermodynamic stability while complexes of H3te3a, particularly Co2+and Zn2+, are even more stable. 31P NMR spectra of the cadmium(II) complex of H5te3a1p showed that the phosphonate moiety was coordinated to the metal ion. The UV-vis-NIR spectroscopic data and magnetic moment values of Co2+and Ni2+complexes of H5te3a1p and H3te3a together with the EPR of the corresponding Cu2+complexes indicated that all these complexes adopt distorted octahedral coordination geometries in solution. This was confirmed by the single crystal structure of [Cu2(Hte3a)(H2O)3Cl]Cl0.5(ClO4)0.5·2H2O that showed two distorted octahedral copper centres bridged by a N-acetate pendant arm with a CuCu distance of 4.890(1) Å. The first one is encapsulated into the macrocyclic cavity surrounded by four nitrogen and two oxygen donors... [ABSTRACT FROM AUTHOR] Copyright of Dalton Transactions: An International Journal of Inorganic Chemistry is the property of Royal Society of Chemistry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts)