title: Novel heterometallic Schiff base complexes featuring unusual tetranuclear {Co(III)2Fe(III)2(μ-O)6} and octanuclear {Co(III)4Fe(III)4(μ-O)14} cores: direct synthesis, crystal structures, and magnetic properties.
abstract: A one-pot reactions of cobalt powder with iron(II) chloride in dimethylformamide (DMF; 1) or dimethyl sulfoxide (DMSO; 2) solutions of polydentate salicylaldimine Schiff base ligands (H(2)L(1), 1; H(4)L(2), 2) based on 2-aminobenzyl alcohol (1) or tris(hydroxymethyl)aminomethane (2), formed in situ, yielded two novel heterometallic complexes, [Co(III)(2)Fe(III)(2)(L(1))(6)]·4DMF (1) and [Co(III)(4)Fe(III)(4)(HL(2))(8)(DMSO)(2)]·18DMSO (2). Crystallographic investigations revealed that the molecular structure of 1 is based on a tetranuclear core, {Co(III)(2)Fe(III)(2)(μ-O)(6)}, with a chainlike metal arrangement, while the structure of 2 represents the first example of a heterometallic octanuclear core, {Co(III)(4)Fe(III)(4)(μ-O)(14)}, with a quite rare manner of metal organization, formed by two pairs of {CoFe(HL(2))(2)} and {CoFe(HL(2))(2)(DMSO)} moieties, which are joined by O bridges of the Schiff base ligands. Variable-temperature (1.8-300 K) magnetic susceptibility measurements showed a decrease of the μ(B) value at low temperature, indicative of antiferromagnetic coupling (J/hc = -32 cm(-1) in 1; J/hc = -20 cm(-1) in 2) between the Fe(III) magnetic centers in both compounds. For 2, three J constants between Fe(III) centers were assumed to be identical. High-frequency electron paramagnetic resonance spectra allowed one to find spin Hamiltonian parameters in the coupled-spin triplet and quintet states of 1 and estimate them in 2. The "outer" and "inner" Fe atoms in 2 appeared separately in the Mössbauer spectra.
authors: Department of Inorganic Chemistry, National Taras Shevchenko University, Volodymyrska street 64, Kyiv 01601, Ukraine.
authors: Eduard N
authors: EN
authors: Chygorin
authors: Oksana V
authors: OV
authors: Nesterova
authors: Julia A
authors: JA
authors: Rusanova
authors: Vladimir N
authors: VN
authors: Kokozay
authors: Volodymyr V
authors: VV
authors: Bon
authors: Roman
authors: R
authors: Boča
authors: Andrew
authors: A
authors: Ozarowski
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D060328:Magnetic Phenomena; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*; D012545:Schiff Bases / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D012545:Schiff Bases; D003035:Cobalt; D010100:Oxygen