Abstract
Five mono-nuclear Cu(II) and Ni(II) complexes and one dinuclear Zn(II) complex were synthesized from the Schiff bases N,N'-bis(3-ethoxy-2-hydroxybenzylidene)-1,2-phenylenediamine (H2LOEt-phda) and 2-ethoxy-6-({2-[(3-ethoxy-2-hydroxybenzylidene)amino]-benzyl}iminomethyl)phenol (H2LOEt-ambza): [Cu(LOEt-phda)(H2O)].H2O (1), [Ni(LOEt-phda)].H2O (2), [Cu(LOEt-ambza)].H2O·EtOH (3), [Cu(LOEt-ambza)].H2O (4), [Ni(LOEt-ambza)] (5) and [Zn2(LOEt-ambza)(μ-OAc)(OAc)] (6). The complexes were structurally characterized with elemental microanalyses, IR, UV-Vis and ESI-MS spectroscopic techniques as well as single crystal X-ray crystallography. The metal centers display distorted square planar geometries in 2–4 and 5 and distorted square pyramidal (SP) in 1, whereas in 6 an intermediate geometry between SP and TBP was observed around the first Zn2+ ion and a tetrahedral around the second ion, with one acetate is acting as a bridging ligand. In all cases, metal ions were incorporated into the N2-O2 binding site with no involvement of the alkoxy groups in the coordination. The LOEt-ambza-complexes 3–6 revealed significant dihedral angles between the phenol rings and the plane containing the central benzene ring, and large O2-O2 bond distances (5.1-5.9 Ǻ). Results are discussed in relation to other related Schiff base complexes.
Highlights
Polynucleating ligands are a class of compounds that are able to simultaneously bind two or more metal ions leading to the formation of di- or polynuclear metal complexes
Five mononuclear Cu(II) and Ni(II) (1–5) as well as a dinuclear Zn(II) (6) derived from the Schiff bases H2 LOEt -phda and H2 LOEt -ambza were synthesized and structurally characterized where the metal ions are bound through the N2 -O2 bonding site without the involvement of the alkoxy groups into the coordination
Many of such Schiff base complexes have been isolated with 3d, 4f and alkali metal ions [7,10,17,18,20,21,22,23,24,30,31,32,40,41,42,56,57,58,59,60]
Summary
Polynucleating ligands are a class of compounds that are able to simultaneously bind two or more metal ions leading to the formation of di- or polynuclear metal complexes Among many of these compounds which are widely used are those emerged through the Schiff base condensation reactions of diamines (ethylenediamine, en; propylenediamine, tn; 2,2-dimethylpropylenediamine, dmtn; o-phenylenediamine, phda and o-aminobenzylamine, ambza) with 2-hydroxy-3-alkoxybenzaldehyde (Scheme 1) in ethanol or methanol [1,2,3,4,5,6,7,8,9,10,11,12,13]. The rich diversity of the Schiff base metal complexes constructed from 3-alkoxysalicylaldehyde led to the isolation of fascinating coordination compounds [14,29,30,31,32,36,37,38,39].
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