The reactions of elemental iron with dipicolinic acid (H2dipic) and quinaldic acid (Hquin) -: X-ray crystal structures of [C5H5NH][Fe(Dipic)(Hdipic) (C5H5N)2]•3C5H5N, [Fe2(μ-O)(Dipic)2(C5H5N)4]•2C5H5N•2H2O and trans-[Fe(Quin)2(MeOH)2]

Iron powder reacts with dipicohnic acid (H(2)dipic) in pyridine at 110degreesC to give the heptacoordinate iron(II) complex [C5H5NH][Fe(dipic)(Hdipic)(C5H5N)(2)]; the (Hdipic)(-) ligand binds to the metal centre solely through the oxygen atoms of one carboxylate group, the first example of this coordination mode at iron. Upon dissolution in pyridine under aerobic conditions this complex transforms into the oxo-bridged diiron(III) species [Fe-2(mu-O)(dipic)(2)(C5H5N)(4)], which possesses a linear Fe-O-Fe axis. Quinaldic acid (Hquin) reacts with iron powder in pyridine at 110 degreesC to give [Fe(quin)(2)(C5H5N)(2)], analogous to the corresponding reactivity of picolinic acid. This complex is converted into trans-[Fe(quin)(2)(MeOH)(2)] or [Fe-2(mu-O)(quin)(4)(dmf)(2)] in methanol or DMF respectively. The formation of an iron(II) complex in the reaction with methanol differs markedly from the picolinate system. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.