Formation of out of plane oxime metallacycles in [Cu2] and [Cu4] complexes
ABSTRACT The reaction of Cu(ClO4)2·6H2O with dimethylglyoxime (H2dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu2(μ-Hdmg)4] (1). Reaction of 1 with [Cu(bpy)(H2O)2](ClO4)2 (bpy=2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2](ClO4)2 (2). The direct reaction of Cu(ClO4)2·6H2O with H2dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N−O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN4O coordination spheres and complex 2 consists of a dicationic [Cu4(μ-Hdmg)2(μ-dmg)2(bpy)2(H2O)2]2+ unit and two uncoordinated ClO4− anions having CuN4O and CuN2O3 coordination spheres. The two copper(II) ions are at a distance of 3.846(8)Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10)Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–Noxime distances are 1.953 and 1.935Å, respectively. The average basal and apical Cu−Ooxime distances are 1.945, 2.295 and 2.429Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H2O)2]2+. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77K consist of axially symmetric fine-structure transitions (ΔMS=1) and half-field signals (ΔMS=2) at ca. 1600G, suggesting the presence of appreciable Cu–Cu interactions.
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ABSTRACT: The reactions of the Schiff-base ligands 3-(4-methylimidazol-5-yl)methylenehydrazonobutan-2-one oxime (LH) and 3-(1-methylimidazol-2-yl)methylenehydrazonobutan-2-one oxime (L′H) with copper(II) perchlorate hexahydrate and copper(II) nitrate trihydrate in a 1:1 molar proportion in methanol gave rise to [Cu2L2(H2O)2](ClO4)2 (1a), [Cu2L2(H2O)2](NO3)2·1.5H2O (1b), [Cu2L2′(H2O)2](ClO4)2 (2a) and [Cu2L2′(NO3)(H2O)](NO3)·0.5H2O (2b) in substantial yields. The complexes have been characterized by C, H, N microanalyses, ESI-MS, FTIR, UV–Vis spectra, conductivity measurements and room temperature magnetic susceptibility and EPR measurements. The X-ray crystal structures of two (1a and 2b) of the complexes have been determined. 1a and 2b are oximato bridged Cu(II) dimers. Variable temperature magnetic studies on 1a, 2a and 2b manifest that the Cu(II) centers are antiferromagnetically spin coupled. The electrochemical studies show a Cu(II) to Cu(I) reduction in methanol. The thermal behaviors of 1b and 2b have also been studied.Polyhedron 08/2011; 30(13):2310-2319. DOI:10.1016/j.poly.2011.06.024 · 2.01 Impact Factor
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ABSTRACT: The oxido-pincer ligand pydotH2 (2,6-bis(1-hydroxy-1-o-tolyl-ethyl-η2O,O′)pyridine) forms two different CuII containing complexes when prepared from anhydrous CuCl2. A combination of EPR spectroscopy and EXAFS allowed to structurally characterise the light-green dimer of the formula [(pydotH2)CuCl(μ-Cl)2ClCu(pydotH2)] and the penta-coordinate olive-green monomer [(pydotH2)CuCl2]. The molecular entities imply that the ligand remains protonated upon coordination. When dissolved in DMF both compounds form monomeric species [(pydotH2)CuCl2(DMF)] which could be characterised in detail by EPR, UV–Vis/NIR spectroscopy and electrochemical measurements. The assignments were supported by comparison with CuII complexes of the related ligands 2,6-bis(hydroxymethyl)pyridine (pydimH2) and 2,6-bis(1-hydroxy-1-methyl)pyridine (pydipH2).Polyhedron 01/2012; 31(1):649–656. DOI:10.1016/j.poly.2011.10.023 · 2.01 Impact Factor