Abstract
A series of bimetallic zinc(II) and nickel(II) complexes based on the novel dinucleating unsymmetric double‐Schiff‐base ligand benzoic acid [1‐(3‐{[2‐(bispyridin‐2‐ylmethylamino)ethylimino]methyl}‐2‐hydroxy‐5‐methylphenyl)methylidene]hydrazide (H~2~bpampbh) has been synthesized and structurally characterized. The metal centers reside in two entirely different binding pockets provided by the ligand H~2~bpampbh, a planar tridentate [ONO] and a pentadentate [ON~4~] compartment. The utilized ligand H~2~bpampbh has been synthesized by condensation of the single‐Schiff‐base proligand Hbpahmb with benzoic acid hydrazide. The reaction of H~2~bpampbh with two equivalents of either zinc(II) or nickel(II) acetate yields the homobimetallic complexes [Zn~2~(bpampbh)(μ,η^1^‐OAc)(η^1^‐OAc)] (ZnZn) and Ni~2~(bpampbh)(μ‐H~2~O)(η^1^‐OAc)(H~2~O) (NiNi), respectively. Simultaneous presence of one equivalent zinc(II) and one equivalent nickel(II) acetate results in the directed formation of the heterobimetallic complex [NiZn(bpampbh)(μ,η^1^‐OAc)(η^1^‐OAc)] (NiZn) with a selective binding of the nickel ions in the pentadentate ligand compartment. In addition, two homobimetallic azide‐bridged complexes [Ni~2~(bpampbh)(μ,η^1^‐N~3~)]ClO~4~ (NiNi(N~3~)) and Ni~2~(bpampbh)(μ,η^1^‐N~3~)(MeOH)~2~~0.5~(N~3~)~0.5~ (NiNi(N~3~)(MeOH)~2~) were synthesized. In all complexes, the metal ions residing in the pentadentate compartment adopt a distorted octahedral coordination geometry, whereas the metal centers placed in the tridentate compartment vary in coordination number and geometry from square‐planar (NiNi(N~3~)) and square‐pyramidal (ZnZn and NiZn), to octahedral (NiNi and NiNi(N~3~)(MeOH)~2~). In the case of complex NiNi(N~3~) this leads to a mixed‐spin homodinuclear nickel(II) complex. All compounds have been characterized by means of mass spectrometry as well as IR and UV/Vis spectroscopies. Magnetic susceptibility measurements show significant zero‐field splitting for the nickel‐containing complexes (D=2.9 for NiZn, 2.2 for NiNi(N~3~), and 0.8 cm^−1^ for NiNi) and additionally a weak antiferromagnetic coupling (J=−1.4 cm^−1^) in case of NiNi. Electrochemical measurements and photometric titrations reveal a strong Lewis acidity of the metal center placed in the tridentate binding compartment towards external donor molecules. A significant superoxide dismutase reactivity against superoxide radicals was found for complex NiNi.