Magnetic Properties of bis - o -Benzosemiquinonato Cobalt(II), Iron(II), and Manganese(II) Complexes with 2,2 ' -Biquino
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MAGNETIC PROPERTIES OF bis-o-BENZOSEMIQUINONATO COBALT(II), IRON(II), AND MANGANESE(II) COMPLEXES WITH 2,2¢-BIQUINOLINE AND 1,4-DI-tert-BUTYL1,4-DIAZABUTADIENE N. A. Protasenko and A. I. Poddel’sky
UDC 546.03, 547.024
New heteroligand cobalt(II), iron(II), and manganese(II) complexes of the M(3,6-SQ)2L type bearing 3,6-di-tert-butyl-o-benzosemiquinonato ligands (3,6-SQ) and 2,2¢-biquinoline or 1,4-di-tert-butyl-1,4diazabutadiene-1,3 as neutral ligands (L) have been synthesized and characterized. It was shown on the basis of the magnetic susceptibility measurements and spectroscopic studies that all complexes contain metal(II) ions in the high-spin state and two radical-anionic o-semiquinonato ligands. It was found in the result of analysis of magnetic susceptibility temperature dependence by magnetic coupling parameters modeling that the antiferromagnetic ligand-ligand coupling takes place in the cobalt(II) and iron(II) complexes, while antiferromagnetic metal-ligand interactions dominate in the manganese(II) complexes.
Keywords: transition metals, o-semiquinone, N-donor ligand, magnetochemistry.
For a long time, organic compounds containing a 1,4-diazadiene-1,3 fragment have been used as ligands in coordination chemistry due to their wide capabilities to form coordination bonds. Such compounds form complexes with almost all metals of the Periodic system and successfully act as both the main and additional ligand [1, 2]. Coordination compounds with such type ligands possess a number of interesting and unique properties; some of them find their application in the catalytic processes [3-5] and design of Single Molecule Magnets [6]. Such a variety of applications is explained by the ability of 1,4-diazabutadienes-1,3 to be redox-active “non-innocent”) ligands. In metal complexes they can exist in neutral form, radical anion form after one-electron reduction, or in dianion form after two-electron reduction [7-10]. In the present work we have used two compounds with 1,4-diazabutadiene-1,3 backbone, namely 2,2¢-biquinoline and 1,4-di-tert-butyl-1,4-diazabutadiene-1,3 as neutral ligands for the synthesis of transition metal complexes based on 3,6-di-tert-butyl-o-benzoquinone. Transition metal complexes with redox-active o-quinone type ligands are of significant interest due to the possibility to form various types of compounds with different intramolecular charge distributions [11-13]. The unusual properties of such complexes are determined by the presence of additional magnetic centers between metal ion and new channels for exchange interaction transfer (ligand-ligand, metal-ligand) that determine the ground spin state and magnetic behavior of the complex. Furthermore, as is well known, they have a unique facility for reversible change of the electronic structure under external stimuli (temperature, pressure, photo irradiation, and magnetic field) [14-17]. This phenomenon, called valence tautomerism, was first observed for bis-o-semiquinonato cobalt complex with 2,2¢-bipyridine ligand [18]. The ______________________
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