Directed Synthesis of a Heterobimetallic Complex Based on a Novel Unsymmetric Double‐Schiff‐Base Ligand: Preparation, Characterization, Reactivity and Structures of Hetero‐ and Homobimetallic Nickel(II) and Zinc(II) Complexes

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)](OAc) ( 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 ](ClO 4 ) 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 .