title: Iron(III) activation hits a [4 + 4] macrocycle.
abstract: The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).
authors.affiliation: Institut für Anorganische Chemie der Universität Karlsruhe, Germany.
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Hewitt
authors.forename: Jin-Kui
authors.initials: JK
authors.lastname: Tang
authors.forename: N T
authors.initials: NT
authors.lastname: Madhu
authors.forename: Bernd
authors.initials: B
authors.lastname: Pilawa
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Anson
authors.forename: Sally
authors.initials: S
authors.lastname: Brooker
authors.forename: Annie K
authors.initials: AK
authors.lastname: Powell