High-spin nickel(II) complexes of penta-aza macrocycles: characterization, electronic spectra, and thermodynamic properties

Abstract

High-spin nickel(II) complexes of 15-, 16-, and 17-membered saturated penta-aza macrocycles [1,4,7,10,13-penta-azacyclopentadecane (L¹); 1,4,7,10,13-penta-azacyclohexadecane (L²); and 1,4,7,11,14-penta-azacycloheptadecane (L³)] have been synthesized and characterized. Their electronic spectra, magnetic moments, and heats of formation are reported. The complexes appear to form distorted octahedra in solution, with the macrocycles folded. In the complexes of L² and L³ one six-membered ring apparently lies in the equatorial plane of the molecule. The heats of formation lie in the sequence L¹ < L³ < L². These complexes do not exhibit a positive macrocyclic enthalpy effect.