Square-planar and octahedral nickel(II) complexes of isomeric cis-2,9-bis(aminomethyl)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecanes

Isomeric cis-2,9-bis(aminomethyl)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraa zacyclotetradecanes (6a and 6b) and their octahedral (4) and square-planar nickel(II) complexes (5) have been prepared and characterized. X-ray crysta llographic investigations of the octahedral complexes have confirmed a fold ed conformation of the macrocyclic ring. Protonation of the pendant amino g roups results in a change in the Ni configuration, which is accompanied by a concomitant change of the macrocycle conformation from a folded to a plan ar one. The structures of the protonated, square-planar complexes and of th e free ligands have been established mainly on the basis of their H-1- and C-13-NMR spectra.