Metal Complexes with Macrocyclic Ligands,XVIII. A study of steric effects in the Co2+-, Ni2+- and Cu2+-complexes with 1-(2-aminoethyl)- and 1-(2-dimethylaminoethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane

The two macrocycles 1-(2-aminoethyl)- and 1-[2-(dimethylamino)ethyl]-4, 8, 11-trimethyl-1, 4, 8, 11-tetraazacyclotetradecane, 1 and 2 , respectively, and their metal complexes with Co²⁺, Ni²⁺ and Cu²⁺ were prepared. The different spectral properties of the complexes with these two ligands can be rationalized by assuming that, in the case of 1 , the amino group of the pendant arm is axially coordinated to the metal ion giving a pentacoordinate structure, whereas the dimethylamino group of 2 cannot bind because of sterical hindrance. This is also corroborated by the observation that the complexes of 2 react with unidentate ligands such as N and SCN^? to give ternary species MLX⁺, whereas those of 1 do not. This indicates that the complexes of 1 have no free coordination site, their coordination sphere being completely saturated by the five N-atoms of the macrocycle, whereas the complexes of 2 having a vacant site still can add an unidentate ligand.