Synthesis and properties of a monomeric and a mu-oxo-bridged dimeric iron(III) complex with a tetradentate pyridine amide in-plane ligand. X-ray structure of [Fe(bpc)Cl(DMF)] [H(2)bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene]

The controlled nucleophilic halide displacement reaction of [NEt4][Fe(bpc)C l-2] [H(2)bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene] with Ag ClO4 in MeCN afforded a crystalline iron(III) complex Fe(bpc)Cl . H2O 1. Th e mixed chloro-dimethylformamide (DMF) axially ligated complex [Fe(bpc)Cl(D MF)] (obtained during recrystallization of 1 from DMF; however, it loses DM F quite readily to revert back to 1) has been structurally characterized. I t belongs to only a handful of mononuclear high-spin iron(III) complexes ha ving deprotonated picolinamide ligand. The iron(III) centre is co-ordinated in the equatorial plane by two pyridine nitrogens and two deprotonated ami de nitrogens of the ligand, and two axial sites are co-ordinated by a chlor ide ion and a DMF molecule. The metal atom has a distorted octahedral geome try. Reaction of 1 with [(Bu4N)-Bu-n][OH] in MeOH afforded a mu-oxo-bridged diiron(III) complex, [Fe(bpc)](2)O . DMF . 2H(2)O, 2. The spin state and t he co-ordination environment of the iron(III) centres in 1 and 2 have been determined by temperature-dependent (25-300 K) magnetic susceptibility meas urements in the solid state (Faraday method) and Mossbauer spectral studies at 300 K. Complex 1 behaves as a perfect S=5/2 system, in the solid-state as well as in DMF solution. The two iron(III) centres in 2 are antiferromag netically coupled (J = -117.8 cm(-1)) and the bridged dimeric structure is retained in DMF solution. Bridge-cleavage reactions of 2 have been demonstr ated by its ready reaction with mineral acids such as HCl and MeCO2H to gen erate authentic S=5/2 complexes, [Fe(bpc)Cl-2](-) and [Fe(bpc)(O2CMe)(2)](- ), respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.