Strong antiferromagnetic coupling in doubly N,O oximato-bridged dinuclear copper(II) complexes |
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Authors: | Evangelia S Koumousi Catherine P Raptopoulou Spyros P Perlepes Albert Escuer Theocharis C Stamatatos |
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Institution: | 1. Department of Chemistry, University of Patras, GR-265 04 Patras, Greece;2. Institute of Materials Science, NCSR “Demokritos”, GR-153 10 Aghia Paraskevi Attikis, Athens, Greece;3. Departament de Quimica Inorganica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain |
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Abstract: | The use of di-2-pyridyl ketone oxime, (py)pkoH, and phenyl 2-pyridyl ketone oxime, ppkoH, in copper(II) hexafluoroacetylacetonate chemistry is reported. The reaction of CuCl2·2H2O with one and two equivalents of ppkoH and Na(hfac), respectively, in CH2Cl2 affords the dinuclear complex Cu2(hfac)2(ppko)2] (1) in excellent yield. The replacement of ppkoH by (py)pkoH gives the isostructural compound Cu2(hfac)2{(py)pko}2] (2) in good yield. The CuII atoms in both 1 and 2 are doubly bridged by the oximate groups of two η1:η1:η1:μ2 ppko− and (py)pko− ligands, respectively. The bridging Cu–(R–NO)–Cu′ units are not planar, with the torsion angles being 23.2° (1) and 20.3° (2). A bidentate chelating hfac− ligand completes five-coordination at each square pyramidal metal ion. The hfac−-free reaction system CuCl2·2H2O/(py)pkoH/NEt3 (1:2:1) gives instead the mononuclear complex CuCl{(py)pko}{(py)pkoH}] (3) in very good yield. The CuII atom is coordinated by two N,N′-bidentate (py)pko−/(py)pkoH chelates and a monodentate chloride anion resulting in a distorted square pyramidal geometry around the metal center. Variable-temperature, solid-state dc magnetic studies were carried out on the representative dinuclear complex 1 in the 2.0–300 K range. The data indicate a very strong antiferromagnetic exchange interaction and a resulting S = 0 ground state, which is well isolated from the S = 1 excited state. The J value of −720 cm−1 was derived from the fitting of the experimental data using the Hamiltonian H = −J(S1 · S2). |
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Keywords: | β-Diketonato ligands Crystal structures Di-2-pyridyl ketone oxime Dinuclear copper(II) complexes Magnetochemistry Phenyl 2-pyridyl ketone oxime |
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