Kit for Unsymmetric Dinucleating Double-Schiff-Base Ligands: Facile Access to a Versatile New Ligand System and Its First Heterobimetallic Copper−Zinc Complex

The synthetic route toward new unsymmetric compartmental “end-off” Schiff-base ligands in a straightforward two-step reaction of
2,6-diformyl-4-methylphenol and two different amine components
is presented. To demonstrate the versatility of this method, we
have synthesized two different single-Schiff-base proligands,
Hbpahmb and Hphmb, utilizing (2-aminoethyl)bis(2-pyridylmethyl)amine and (2-aminomethyl)pyridine, respectively. Subsequent
reaction with thiosemicarbazide as the second amine component
leads to the novel unsymmetric double-Schiff-base ligands {1-[3-[2-[bis(pyridin-2-ylmethyl)amino]ethyliminomethyl]-2-hydroxy-5-methylphenyl]methylidene}hydrazine carbothioamide (H2bpamptsc)
and {1-[3-(pyridin-2-ylmethyliminomethyl)-2-hydroxy-5-methylphenyl]methylidene}hydrazine carbothioamide (H2pmptsc). Both ligands
provide two distinctly different coordination pockets:  a rigid
tridentate N,O,S donor set of the hydrazide compartment versus
a rather flexible pentadentate (H2bpamptsc) or tridentate (H2pmptsc)
nitrogen-rich chelating side arm. The reaction of the ligand H2bpamptsc with zinc(II) acetate and copper(II) perchlorate yields
the heterobinuclear Cu−Zn complex [CuZn(bpamptsc)(μ2,η1-OAc)(MeCN)](ClO4) (1).