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

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)(mu,eta(1)-OAc)(eta(1)-OAc)] (ZnZn) and [Ni(2)(bpampbh)(mu-H(2)O)(eta(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)(mu,eta(1)-OAc)(eta(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)(mu,eta(1)-N(3))]ClO(4) (NiNi(N(3))) and [Ni(2)(bpampbh)(mu,eta(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.

Modeling the coordination chemistry of chitosan: Synthesis and characterization of a nickel(II) complex with a 2-aminoglucose Schiff-base ligand

“…Therefore we tested the sign reversal for the D parameter, which led to a worse fit of the magnetic data with a reduced coefficient of determination. The rather large D parameter is consistent with the observed distorted octahedral coordination environment of the nickel(II) ions, and still well within the generally observed rather broad range from À22 to +12 cm À1 [31][32][33]. The associated g value is at the upper limit of the typically observed range from 2.1 to 2.3.…”

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis, Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2‐Aminoglucose Ligand

“…The electronic absorption spectrum of complex 2 in chloroform solution shows two www.chemeurj.org low energy bands at 643 and 1131 nm which are typical for octahedral high-spin nickel(II) ions. [25,26] To our knowledge 2 is the first trinuclear nickel(II) complex based on a carbohydrate ligand system.…”

“…The decrease of the c M T values below 10 K can be attributed to zero-field splitting (ZFS) of the nickel(II) ions. [19,26] According to the (m 3 -OR) 2 Ni 3 core structure of complex 2, representing an isosceles triangle, a two-J model is employed as spin topology (see Figure 8). The corresponding spin Hamiltonian with J A = J 13 = J 23 and J B = J 12 is given in Equation (2) and includes ZFS for the nickel(II) centers.…”

Nickel(II) complexes with Schiff-base ligands derived from epimeric pyranose backbones as 2,3-chelators: modeling the coordination chemistry of chitosan

“…[33][34][35] For the glucosamine-based nickel(II) complex ½NiðHsal NO 2 GlcÞðtptzÞClO 4 , the d-d transition bands are slightly blue-shifted as exemplified by the 3 A 2g ? 3 T 2g transition occurring at 897 nm.…”