Preparation and characterization of mononuclear Co, Ni, and Zn complexes of dinucleating macrocyclic hexaaza-dithiophenolate ligands and their open-chain derivatives

Abstract

The preparation and characterization of mononuclear complexes of the dinucleating 24-membered hexazadithiophenolate macrocycles H₂L² and H₂L³ and their open-chain N₃S₂ analogues H₂L⁴ and H₂L⁵ are reported. The highly crystalline compounds [Ni(L⁴)] (4), [Ni(L⁵)] (5), [Co(L⁵)] (6), [NiH₂(L²)]²⁺ (7), [ZnH₂(L²)]²⁺ (8), and [NiH₂(L³)]²⁺ (9) could be readily prepared by stoichiometric complexation reactions of the hydrochlorides of the free ligands with the corresponding metal(II) dichlorides and NEt₃ in methanolic solution. All complexes were characterized by X-ray crystallography. Monometallic complexes 4–6 of the pentadentate ligands H₂L⁴ and H₂L⁵ feature distorted square pyramidal MN₃S₂ structures (τ = 0.01 to 0.44). Similar coordination geometries are observed for the macrocyclic complexes 7–9 of the octadentate ligands H₂L² and H₂L³. The two hydrogen atoms in 7–9 are attached to the noncoordinating benzylic amine functions and are hydrogen bonded to the metal-bound thiophenolate functions. A comparison of the structures of 4–9 reveals that the macrocycles L² and L³ have a rather flexible ligand backbone that do not confer unusual coordination geometries on the metal ions. We also report on the ability of the monometallic complexes 7 and 8 to serve as starting materials for the preparation of dinuclear complexes.