METAL-COMPLEXES WITH MACROCYCLIC LIGANDS .38. STERIC EFFECTS IN THE COPPER(II) AND NICKEL(II) COMPLEXES WITH TETRA-N-ALKYLATED 1,4,8,11-TETRAAZACYCLOTETRADECANES

A series of tetra-N-alkylated 1,4,8,11-tetraazacyclotetradecanes have been synthesized and their complexation potential towards Ni2+ and Cu2+ studied. In the case of sterically demanding alkyl substituents, such as i-Pr, PhCH(2), or 2-MeC(6)H(4)CH(2), no metal complexes are formed, whereas for substituents such as Me, Et, and Pr, the metal ion is incorporated into the macrocycle, The spectroscopic properties of the Ni2+ and CU2+ complexes in aqueous solution indicate that, depending on the sterical hindrance of the N-substituents, the complexes are either square planar or pentacoordinated. All these Ni2+ and CU2+ complexes react with N-3(-) to give ternary species, the stability of which have been determined by spectrophotometric titrations. The tendency to bind NS decreases with increasing steric hindrance of the alkyl substituents. The X-ray studies of the Ni2+ complex with the macrocycle 11, substituted by two Me and two Pr groups, and that of the Cu2+ complex with the tetraethyl derivative 8 show that in the solid state, the metal ions exhibit square planar coordination with a small distortion towards tetrahedral geometry.