| 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 (H2L1, 1; H4L2, 2) based on 2-aminobenzyl alcohol (1) or tris(hydroxymethyl)aminomethane (2), formed in situ, yielded two novel heterometallic complexes, [(Co2Fe2III)-Fe-III(L-1)(6)]center dot 4DMF (1) and [(Co4Fe4III)-Fe-III(HL1)(8)(DMSO)(2)]center dot 18DMSO (2). Crystallographic investigations revealed that the molecular structure of 1 is based on a tetranuclear core, \(Co2Fe2III)-Fe-III(mu-O)(6)\, with a chainlike metal arrangement, while the structure of 2 represents the first example of a heterometallic octanuclear core, \(Co4Fe4III)-Fe-III(mu-O)(14)\, with a quite rare manner of metal organization, formed by two pairs of \CoFe(HL2)(2)\ and \CoFe(HL2)(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 mu 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 Mossbauer spectra. |
