Metal complexes with macrocyclic ligands. Part XXII. Synthesis two of bis‐tetraaza‐macrocycles and study of the structures, electrochemistry, VIS and EPR spectra of their binuclear Cu2+ and Ni2+ complexes

Publisher Website
Google Scholar
Abstract
The two bis‐macrocycles 4 and 5 in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7‐tritosyl‐1,4,7,11‐tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis‐macrocycles give binuclear complexes with Ni2+ and Cu2+, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni2+ and Cu2+ complexes indicate that both metal ions are in a square‐planar geometry as expected from the results of the analogous complexes with 1,4,7,11‐tetraazacyclotetradecane 7. Cyclic voltammetry and differential pulse polarography of the binuclear Ni2+complexes in CH3CN show a single two‐electron step for ligand 5, whereas two distinct one‐electron redox processes can be observed for ligand 4, indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu2+ complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X‐ray structures of the binuclear Ni2+ complexes with 4 and 5, it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the observations in solution.

This publication has 25 references indexed in Scilit: